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ACOUSTICS m BUILT ENVIRONMENT ADVICE FOR THE DESIGN TEAM SECOND EDITION

Edited by DUNCAN TEMPLETON [This document contains 174

pages

Acoustics in the Built Environment

Page blank in original

Acoustics in the Built Environment Advice for the design team Second edition

Duncan Templeton (Editor)

MIOA, RIBA BArch(Hons),MSc(Acoustics),

Peter Sacre

BSc(Hons), MSc, MbA, CEng, MIMechE

Peter Mapp BSc, MSc (Acoustics), MIOA, MInstP, FInstSCE,AMIEE David Saunders

BSc(Hons), PhD

ArchitecturalPress An imprintof Butterworth-Heinemann Linacre House, Jordan Hill, Oxford 0X2 8DP A division of Reed Educational and Professional Publishing Ltd

A member ofthe Reed Elsevierplc group OXFORD BOSTON JOHANNESBURG MELBOURNE NEW DELHI SINGAPORE

First published 1993 Second edition 1997

© Reed Educational and ProfessionalPublishing Ltd 1997 All rights reserved. No part of this publication

may be reproducedin any material form (including photocopying or storingin any medium by electronic means and whetheror not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of theCopyright, Designsand Patents Act 1988 or underthe terms ofa licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham CourtRoad, London, England W1P9HE. Applications for the copyright holder'swritten permission to reproduce any part ofthis publication shouldbe addressed to thepublishers British Library Cataloguingin Publication Data

A catalogue recordfor this book is available from the British Library Library of Congress Cataloguingin Publication Data A catalogue record for this book is available from the Library of Congress ISBN 07506 3644 0

Composition by Genesis Typesetting,Laser Quay, Rochester, Kent Printed and bound in Great Britain by MPG Books Ltd, Bodmin, Cornwall

Contents

Acknowledgements vi

Chapter3: Services noise andvibration 85

Contributors vii

Peter Sacre and Duncan Templeton Background; Setting design objectives; Design considera-

Introduction

Chapter4: Sound systems 110

1

tions; Vibration; Installation; References Peter Mapp

Chapter 1: Environmental acoustics 7 Peter Sacre Environmental

Introduction; System planning; Design principles; System design and components; Speech intelligibility; References

appraisals; Site analysis; Transportation noise; Construction noise; Industrial noise; Leisure noise; 5: Technical information 132 Groundborne vibration; New developments as a noise Chapter David Saunders source; References Definitions; Equivalent Standards; International Standards; German National Standards; American National acoustics 35 Standards Institute; American Society for Testing and 2: Chapter Design Duncan Templeton Materials Standards; French Standards; British Standards Sound insulation; Sound absorption; Criteriafor different Index 161 building types; References

Acknowledgements

are indebted to colleagues who have given us assistanceandadvice during the compilation of this book including as follows: Calvin Beck of United Cinemas International; David Belton of BDP; Ian Blackburn, DirectorofBuilding Development, Royal Albert Hall;Jeff Charles of Bickerdike Allen Partners; Richard Cowelland Rob HarrisofArup Acoustics;Laurence Haslem of Sandy Brown Associates; Niels Jordan of Jordan Akustik; Professor Peter Lord of the Universityof Salford Department ofApplied Acoustics andBDPAcoustics;Rob Metkemeijer of Peutz & Associés BV; Victor Robinson of Robinson & McllWaine;Eve Templeton.

We

Contributors

Duncan Templeton Peter set up his own practice in 1984, to specialize in As a specialist practising architect, Duncan Templeton, sound system design and room acoustics. Before this he BArch(Hons), MSc(Acoustics),MIOA, RIBA, is Director worked for two of the UK's largest general acoustic of BDP Acoustics Ltd (a subsidiary of Building Design consultancies,where he was involvedwith all typesofnoise Partnership, the largest architectural practice in the UK). control and architectural projects.

Feasibilitystudies have included investigationsand prediction work at Royal Albert Hall, Royal Festival Hall, and Royal Opera House. Theatre and conference consultancies include The Swan, High Wycombe; North Wales Theatre, Llandudno; garrison theatres at Rheindahlen andHerfordin Germany.Music consultancies include the new City of Leeds College of Music building and Tonbridge School Chapel, Kent. TV work clients comprise Granada Television, BBC, and Yorkshire Tyne-Tees Television. Environmental expert testimony topics include quarries, wind farms, andtransport interchanges. He is a visiting lecturer at Humberside and Lincolnshire University, and the UniversitiesofManchester andSalford.He is the co-author ofthree books on architectural acoustics:

He has a particularinterest in the loudspeaker/room interface, and in speech-intelligibilitymeasurementand prediction. He has presented papers and seminars on these topics both in the UK and abroad. Peter regularly carries out technical reviews for a numberofpublications, andis the author ofmore than 40 articles and papers. He has contributed to three international references on acoustics and electroacoustics. Sound systems with which Peter has been involved include: the Queen Elizabeth Conference Centre; the Royal Hong Kong Jockey Club Stadium; plus the Broadgate Arena, the British Museum, and Waterfront Hall, Belfast.

DetailingforAcoustics, The ArchitectureofSound, andAcoustic Design.

Peter Sacre Peter Sacre, BSc(Hons), MSc, MbA, CEng, MIMechE, has been employed in the field ofacoustic consultancy for 20 years. He is presently responsible for managing the Wilmslow office of Sound Research Laboratories Ltd, having been an Associate of BDP Acoustics Ltd and head ofthe Acoustics Departmentat WimpeyLaboratories Ltd. He is involved primarily with environmental, planning and architectural projects. Tasks he has undertaken include environmental assessmentsfor the ChannelTunnel fixed link and the subsequent acoustic design of the Folkestone Terminal, extensive noise monitoring around RAF airfields, design and supervision of acoustics for the Queen Elizabeth Conference Centre, predictions for the South Warwickshire Prospect coal mine, and a coalloading facility and open-cast mine in NSW, Australia, when he was resident there. Peter Mapp Peter Mapp, BSc, MSc (Acoustics), MbA, MInstP, FInstSCE, AMIEE, is an independentacoustics and sound systemsdesign consultant.

David Saunders

DavidSaunders graduatedfrom the UniversityofNottingham in 1964 with a first class honours degree in Physics. He was awarded a PhD from the Universityof St Andrews in 1967 for a research project in solid state physics. He thenjoined the Physics Departmentat the Universityof Salford to work with a small group doing researchin the field of building acoustics. This group developed and in 1975 the DepartmentofApplied Acoustics was formed. It is now the secondlargest acoustics research and teaching department in the UK, and David is now Head of Department. His original research was concerned with subjective reaction to noise and vibration and general building acoustic problems. However, for the last eight years his interest has been in studying the propagation and effects of high level impulsive noise. His consultancy experience covers a wide range of environmental and noise control problems, in particular the assessment of the impact of transportation and industrial development. He has carried out work for industry, local government, building and architectural firms andlegal organizations, and has representedclients at planningapplications and appeals.

Introduction on acoustics fall into several

stereotypes: the the the glossy, and mathematical/theoretical, primers, the practical. The glossy may centre on auditoria, the practical on services noise, but it is difficult to find a really useful day-to-day reference covering a range of acoustics issues in the building technology in its widest sense. Sound is different to each discipline: to a sociologist it is a stimulus eliciting a range of subjective responses, to a physicist it is a measurable phenomenon with varying propagatory character, to the structural engineer vibration is the issue, to the mechanical engiBooks

neer it is noise control. Environmental noise matters transportation, industry— may impinge on the planner's —

considerations. The architect may come across sound as a characteristic ofkey spaces (e.g. studios, auditoria) and in providing adequate isolation and privacy to areas within a building. What seems to be wanted, and does not exist, is a technical thesaurus covering practical reference needswithoutflannel and undue mathematics, offering concise guidance and assisting in design meth-

Figure 1.1 RAG Walsall — external. Challenge ofkeeping out motorway noise

odology. A designer does not want to calculate from basic theory how a partition assemblywill achieve certain sound insulation values; he will want to check his design intent against performance tables, have some idea from other tables about the internal needs and externalnoise exposure, and either adjust his design or use the data as a performancespecification for suppliers to implement. The need for value for money in noise control and general acoustic design, i.e. to justifi a level of performance to a client and avoid overkill,shouldbe recognized, with the emphasis on consistent standards, evenly applied, for maximum effect.

Figure 1.2 RAG Walsall — internal. Challengeofseparatingengine test beds from office areas

2

Acousticsin the Buift Environment

The scope for advice is more and more apparent: the environment is getting noisier, the standards demanded higher, ventilation andsound systems more sophisticated, computer-aided instrumentation and prediction techniques more reliable and accurate (Figures 1.1 and 1.2). We want this book to appeal to a wide audience — clients, project managers, and students, as well as architects, mechanical, electrical and sound system engineers. Eachofthe headings generates a separate approachand different disciplines can refer to the relevant chapter, although there is a greatdealofoverlap (Diagram 1.1). The clean ideals of theory are inevitablycompromised on the rack offast tracksite progress;judgementsandadvicehave often to be given based on half-truths and inadequate information. Good acoustic study techniques are sometimes too cumbersome: on a recent auditorium physical modelling exercise, the project was tendered before research results could be applied. If advice in this book nudges designers and engineers in the right direction once in a while,that is asmuchas we couldexpect. Timelyadvice duringthe design, construction, and early use ofbuildings is the aim (Diagrams1.2 —1.4). As practising acousticians we come across 'runs' of design issues in design sectors. In offices it may be 'how noisy can it possibly be before the building has to be sealed rather than naturally ventilated to the perimeter?'

The cost constraints are such that developers are very reluctant to have sealed buildings in speculative offices. Similarly, hotels sprout on busy interchanges to catch the passing trade, and commercial business parks crowd the airports. Leisure centres group innovative combinations

of noisy activity.

Many developments are of such a scale now that new infrastructure — transport, landscape and topography — is entailed long before the building work starts. Many building complexes are of such a scale that the initial contractis a mere shell for fit-out contracts by numerous tenants, so there is a shift in the approachto lookingafter the client's interests. Novel building types, like trading rooms, microchip production facilities, multiplex cinemas and theme parks, demand assessment in the absence of published data. Relationships to other professions can get complex (Diagram 1.5). Legislation is a key issue, not only because of the closer compatibility to European standards, but also because of far-reaching statutes, for example the Noise Act 1996, the Noise at Work Regulations and the Town and Country Planning (Assessment of Environment Effects) Regulations. The first gives local authorities powers to fine peoplewho create excessive noise at night and confiscate noisy equipment,the second tightens the legal duties of employers, designers, manufacturers and suppliers, to

• Classification • Airborne noise • Vibration

C a,

o >0 £

• Transportation

CO

LU C

Impact

I

Cl'

Cd

a

0 0

Transportation, industrial premises, ground vibration Roads + 15 years of development — break-out at boundary Site planning, zoning to road noise, Natural or mechanical location of plant rooms — roof, basement,integral

HVACnoise

Cd

ou .9)

• Planning •• Screening • Ventilation Plant •• Room acoustics insulation •• Sound Sound systems

Rural, industrial

•5

>

• Workmanship • Manufacturer selections

• HVAC noise •• Room acoustics Separation • Trouble shooting • Remedialwork Diagram 1.1 Checklist: stages ofdesign

Compared to criteria

Introduction CONSTRUCT

BUILDING IN USE

Diagram 1.2 Regulatory authorities and examples oflegislation

-

BUILDINGTYPE PLANNING

BUILDING CONTROL

Town & Country PUBLIC

Control of Pollution

Planning Act, 1971

ENVIRONMENTAL HEALTh

S.29

Act 1974

FACTORY

Offices, Shops and

Licensing

Railway

justices

premises Act, 1963 S.21

Town& Country

S.38, 62, 68 Control ofsources ofnoise and vibration S60, 61 Limits on site Construction noise

(Scotland) Acts, 1972, 1977

COMMERCIAL

OTHER

INSTALLATIONS

Public Health Acts, Amendment Act, 1980 Private Places of Entertainment

(Licensing) Act, 1967 Late Night Refreshment Houses Act, 1969

Town& Country

INDUSTRIAL

Environmental

Planning (Assessment of Environmental Effects) Regulations 1988 BS4142: 1990

Protection

1990 BS 5228: 1997NoiseControl on Construction and oDen sites Noise and Statutory Nuisance

DOE circulars 10/73

SDD circular 23/73 Noise Insulation Regulations 1975

Health and Safety at Work(etc.) Act, 1974 EECdirect /188

Act 1993

2/76 1/85

DWELLINGS

Act

TheNoise Act 1996 Building Regulations 1992. SoundE1/213 Building Standards (Scotland) Regulations 1981 Building Regulations (NI) 1971 as amended.

HEALTH

Noise at work HSE guidance/ Regs 1990

Hospital design note 4 (Amendment HN 76/126) DHSSDATA sheet DH1.2

Diagram 1.3 Statutes: sample reference publications

4

Acoustics iii the Built Environment

I I

DESIGN/SUPERVISE ________________________________________________

CONSTRUCT/INSTALL

DESIGN

I

________________________________________________

_______________________________________

I

TENDER

___ ___

I I I

_________________________________________________________

COMPONENT SELECTION

SUPPLIER/ SUBCONTRACTOR APPOINTED

________________________________________________________

_______________________ I I

I

CHECK TOTAL SYSTEM I

SUPPLY SAMPLES

__ I

I

LABORATORY TESTS, VALIDATION

I

__

I

_______________________

I I

_______________________

WORKMANSHIP ___________________________________________

STS OR

WITNESSING

I

________________

Diagram 1.4 Designand construction stages

MAINSTREAM PROFESSIONS

ARCHITECT

QUANTITYSURVEYOR TOWN PLANNER

RICAL \

MECHANICAL ENGINEER ENGINEER CIVIL ENGINEER STRUCTURAL ENGINEER LANDSCAPE ARCHITECT

\

I I I I I I

MANAGER

PROJECT

-

__________________________________

GENERAL PRACTICE

I I

_

SPECIALIST CONSULTANTS

_________________________________________________

LIGHTING ACOUSTIC ENERGY SYSTEMS DUST/POLLUTION

_________

SPECIALIZATION

Diagram 1.5 Design disciplines: context ofacoustic consultancyto other skills in the buildingindustry

minimize hearingdamage; the third defines environmental assessment for any major projects of more than local importance or projects in sensitive areas. Newor amended legislation is available relating to key aids, for example part E ofthe Building Regulations, BS 4142 and BS 6472. Legal processes for noise abatement of course deserve proper legal advice, but ChristopherPenn's The Law and its Enforcementis a useful starting point. 'Environmental acoustics' covers a topic largely overlooked to date but is a growth areain consultancy because of the real concern that Green issues raise. Increasingly, road noise is universal and there are few truly quiet spots left on the mainland UK. Thirty-two million people are exposed to 'high' (55—75 dBA) levels of noise. Protection techniques to properties alongside roads vary from UK rustic timberto Swiss curved glazing. Environmental noise has become an everydayissue: in 1978, there were 17980 complaints to local authorities about environmental noise. By 1982, the number ofcomplaints had grown to 33014, rising each year to reach 111 151 in 1993, and nearly 145000 in 1994, the last year that statisticsare available. 'Design acoustics' too has been well served in publications but the authors feel there is increasing need for more detailed advice specific to buildings' uses; one can no longergeneralize andsuggest a single set ofcriteria for say studios or practice rooms. More and more, the designeris setting performancecriteria only, for specialist suppliers and installers to implement. 'Services noise and vibration' have been reasonably served by a number of publications to date, for example the Sound Research Laboratories' NoiseinBuildingServices and Beranek and Ver's Noise and Vibration Control Engineering Chapter 3 complements existing advice rather than competes. An increasing proportion of buildings are mechanically ventilated, and economic and space pressures lead to a tendency to higher velocity duct systems where good control is critical. 'Sound systems' have been considered in systems manuals and electronics guidesbut the applications here of interest relate to speech intelligibility (PA), audibility (fire alarms), sound quality in particular spaces (sound reinforcement) and electroacoustics (modifring the way auditoriasound),applications directly related to building projects and to acoustics, rather than attemptingto cover the rapidly-changing equipmentfield. There are a number ofprofessionswith a useful half-knowledge— electrical engineers, systemsspecialists, theatre consultants — butthe areafalls dangerously between professions as regards full

and reliable documentation; it becomes all too tempting to 'leave it to the trade'. Sound systems are an intrinsic part of any modern performancespace.

Professor Stephen Hawking, who popularized cosmology and astrophysics with a bestseller, A BriefHistory of Time, was advised by his publisher that 'each equation included would halve the sales'. Perhaps the publisher has the last laugh, as the 1996 version is An Illustrated Brief History of Time. Our objective has been to produce reference material of the greatest use in an attractive format— with minimal essentialformulaesupportingthe methodology. In Chapter 5 we address the working knowledge of acoustic terminology, relevant standards in the UK and worldwide, and up-to-date information sources. Some of the topics arise from the course notes for a university degreein acoustics.Sucha courseis a general grounding for acoustics, as opposed to being specificallyrelated to the built environment. The technology and analysis techniques are advancing quickly, so there will be in the near future more data available to analyse, define and accurately commission criteria set on projects. Acoustic measurement equipment has reduced in weight and size dramatically, while its ability to collect, and hold in memory, data has increased equally dramatically.Chapter 5 is a summary ofdefinitions overlapping with the topics covered in the chapters, intended as a quick reference source to ensure that terms quoted in performance specificationdocuments are correctly ascribed, or alternatively to interpret, in a dictionary style, terms comeacross in contractdocuments or technical reports. The most relevant standards have been selected and it has been a difficult decision to decide how much to include on this; database keywords generate many hundreds of standards but the 'first port of call' reference should be given otherwise any oracle referred to will be too broad andmeaningless. A problemwith quotinglarge numbers of standards is the constant updating; any standardquoted herein should therefore be checked for any amendments subsequent to publication. The humorist Max Frisch defined technology as 'the knack of so arranging the world that we don't have to experience it'. This book tries to make design acoustics less of a black art or science, by giving concise and economically reasonable advice, topic by topic. This secondedition, promptedby the sell-outofthe first, allows general updating of references and guidance with the introductionof some newcase studies.

Page blank in original

Chapter acoustics

1

Environmental

Peter Sacre

This chapterlooks at the need for an acoustic appraisal, what needs to be considered for a site inspection or survey, the types of environmental noise sources that could be encountered, and identifies those factors that need to be considered when investigatingthe impact of a development on its surroundings, including environmental impact assessments.

Needfor an acoustic appraisal An appraisal may be required for one of the following reasons: to assess possible site constraints Environmental appraisals as part ofan Environmental Statement to accompany a Planning Application. Introdudion The initial assessment that needs to be made for any In the latter case, an acoustics assessmentcouldbe oneof development takes accountof its location in the environ- several issues to be covered or it may be required as an ment. Thus environmental acoustics needs to be con- independentstudy. sidered at the outset, whether it is the consideration of The route taken to identify the need for an appraisal is planningissues which take accountof the possible effect shown on Diagram 1.1. of a development on its surroundings or whetherit is the effect of an external noisy climate on that proposed Specialist help Once the need for an acoustic appraisal has been agreed, development. The need to considerenvironmental acoustics has been specialist advice is available from a number of acoustics given more emphasis now that environmental issues consultants. These can be found via professional bodies generally are ofuniversal concern.The publication of the such as the Institute of Acoustics or the Association of Government's White Paper on the Environment [1] Noise Consultants. Often the local authority will keep a added weight to this consideration by requiring an register ofacoustics consultants ableto undertakeappraisenvironmental assessmentfor significant schemes. als within their area.

• •

Effect on External noise

or vibration

e.g. Transportation, industrial,

I construction, mineral extraction sources

Diagram 1.1 Acowstic appraisal:need

8

Acoustics in the Built Environment

Site survey/inspection

J Set design criteria

Acoustic appraisal

______

Predict noise/vibration climate

Assess climate against criteria

details. Although it would be possible to undertake prediction withoutmeasuredsite data in situations where there is sufficientlyreliable publishedinformation, e.g. noise due to road traffic, a site inspection would provide site-specific factors which would assist in the exercise. Prediction ofvibration on a site is extremely complicated and measurement must always be the preferredmethod. The differences between the predictednoise or vibration climate and the design criteria will identify the scale of any potential problem. An assessment will need to determine whether any additional control measures are necessary and practicable. Obviously, small differences may not warrant huge expenditure and agreementmust be soughtwith all interested partiesto determinethe best courseofaction. Wherecontrol methodsare required,the appraisal should identify the best methods.

Identify noise control

Diagram 1.2 Acowstic appraisal: requirements

Site analysis Site inspection

Theappointmentofanacoustic consultant canbedirect The site survey is probably the most importantpart of an to theclientoron asubcontract basisto thelead consultant acoustic appraisal, whetherit is only a site inspection or a full measurement survey, since it will determine the (often the architect),as part ofa design team. location of noise-sensitive areas and noise sources and other local factors needed to make an accurate assessMethod ofacoustic appraisal The basic requirements ofan acoustic appraisal are shown ment, e.g. local shielding. If a full survey is being in Diagram 1.2. undertaken, the initial site inspection or pilot survey will The site survey or inspection will enable importantsite- identify the preferred measurementlocations. The items that needto be considered in undertakingan specificinformation to be obtained, suchas whetherthere are any local noise and/or vibration sources which may inspection are identified in Diagram 1.3. Diagram 1.3 also affect any new development, e.g. transportation routes or gives a checklist of the likely aims of an inspection. This industry, or whether there are any nearby noise-sensitive includes reference to local topography, particularly embankments or cuttings, which would provide significant areas, for example housing. In setting design criteria for a development, reference acoustic shielding but the details ofwhich would not easily will need to be made to such documentationas British be determinedfrom maps or plans. In determining noise Standards, to establish acceptable intrusive noise or from transportation routes,data suchas type andgradient vibration levels in a development, or possibly planning ofroad or type ofrailway trackproximity to airports— civil conditions, which ensure that a development will not or military — need to be obtained. affect a nearby noise-sensitive area. In some cases, Measurement locations need to be selected to be researchstudies may need to be referred to in addition to, representative of the local noise or vibration climate and or in the absence of, relevant standards. take account of site practicalities. This would include A prediction exercisewould, in the majority ofcases,be whether noise measurements need to be made at heights based on measured data taking account of site-specific greater than 1.5 m to obtain appropriate data. Short-

Site inspection to determine:

Obtain base data including up-to-date plans identifying site location

•• Development location Location of nearestdwellings or otherbuildings and Contact local authority to discuss local factors i.e. • Noise-sensitiveareas periods of operation —--. •• Noise-producingactivities near the site •• Major noise/vibration sources in area Vibration sources Complaints received •• Local topography routes •• Transportation Measurement locations Indicative noise levels by short measurement Organize site access and check that abnormal activities such as site investigations will not be taking place

Diagram 1.3 Site inspection

Environmental acoustics

period indicative measurements taken during a site inspection are helpful and can establish the preferred monitoring locations. The siteinspection also serves to identif'whetherthere are any local activitieswhich couldaffecta fullsurvey, e.g. transportation maintenance or industrial down-time period. Contact with local authority

Contact with the local authority, normally the Environmental Health Department (EHD), to discuss acoustic appraisal is necessary at some time during the contract. It is desirable therefore to agree any local factors that could affect the survey, including planning conditions. The EHD can identif' the nearest noise-sensitiveareas and/or any major noise/vibration sources in the area. It is also beneficial to know the pattern of complaints arising from noise nuisance. Activities affecting the site

It is necessary to obtain, preferably before a full survey, the likely operating hours of a nearby industrial development or the likely movements on a transportation route, e.g. for railways the number of passenger and freight trains during certain periods should be obtained from Rail Track or the local railway, since the information collected on a particularday may not representthe total picture.

Prior to any site visit, access to the site must be ensured possible. This will normally be by contact with the landowners or estate/lettingagents. This contactwill also need to be made before a site survey is undertaken to ensure that there are no other siteactivities taking place to invalidate the measurements, for example a clash with any site investigation must be avoided. Survey procedure

Once site access has been arranged and the presenceof any activities either on or close to the site has been checked, the basic survey requirements are as illustrated in Diagram 1.4 and as discussed below.

Select noise and vibration measurementlocations, preferably in agreementwith the local authority Determine duration of the survey, e.g. 2 h or 2 days or 2 weeks and sampling, e.g. 10—15 mm or continuous

[ Check weather to avoid windy or rainy conditions Select measurementsunits

[ Select equipment types

1

1

Keeping records of results and events Analysis of results Reporting

1

I

Measurement locations

Measurement locations should be agreed between all parties. Their selection will be basedon the site inspection and take account of site practicalities. For example, it is notalways best to set up equipment close to houses where dogs are present (although it could be argued that they couldbe considered as partofthe environment, it is likely thatbarkingis caused by the presenceofthe surveyor) but to selecta representative equivalent location. Temporary shielding of a potential noise source may also affect the measurements, and locations should be avoided if they screen a noise source. An example of temporary shielding is a builder'sstockpile of materials. A noise measurement location should always be selected with an unobstructedview of the proposeddevelopment and preferably at least 3.5m from a reflecting surface. In the case of nearby housing, it is often the first floor windowsthat are the most sensitive, i.e. bedrooms. Typicallythe heightsofmicrophones will be set at 1.2 m or 1.5 m above ground which correspond to a reception point at the ground floor level of a building. For a receptionheight at first floor level, a microphone height of 4.0 m or 4.5 m above ground using a stand extension may be more appropriate. If greaterheightsneed to be considered for a reception point, e.g. to representthe third floor height ofa building affected by road or railway shielded by a barrier at ground floor height (see Figure 1.1), then a hydraulic mast, which can typically go up to lOm to 12m in height, may be required. In order to reduce the amount of measurement equipment needed to measure at several locations, a primary location could be selected where continuous monitoring is carriedout, togetherwith satellite locations where regular but not continuous measurements are obtained. Typically, the primary location would be unmannedand the satellite locations manned. It may be possible, if a refurbished development is proposed, to use the existing building and position a microphone out of a window, at a distance of about 1 m from the facade. In this case an allowance for facade reflection will need to be made of approximately 3dBA. Once the distance is greater than 3.5m from a reflecting surface, the measurements obtainedat these locations will berelativelyfree-field.Sometimesa distance of10m from a reflecting surface is adoptedforfree-field measurements. Determination of groundborne vibration would typically be in order to assess its impact on a proposed development. Monitoring would need to take place at the part of the proposeddevelopment nearest the sourceand then at regular distances awayfrom the source. Vibration measurements should be made ensuring that the transducer is coupled effectively with the ground, or the surfaceto be measured. A heavy block placed in the soil is typically used to fix a transducer for ground measurements with the ability to allow measurements in the vertical, radial and transverse directions. Duration ofsurvey

I

Diagram1.4 Survey procedure

9

To determine the measurement periods required, it is necessary to identify the periods of operation of the proposed development and any noise/vibration sources nearby. For example, the likely operation of different

10

Acoustics

in the Built Environment

*—Preferred microphone position Second floor unshielded First and ground floors shielded

PROPOSED DEVELOPMENT

BARRIER

e.g. fence or earth bank

NOISE SOURCE

e.g. road or railway

Figure 1.1 Elevated monitoring need

mechanical services plant for an office development will affect the noise climate at different times of the day. The use of a development 24 h/day, 7 days/week, would also identi1' the need to survey at weekends. Typically, consideration needs to be given to assessment at night and the lowestambient/backgroundnoise levels normally occur between 02:00and04:00 hours. However, if the background noise levels are very low between 02:00 and 04:00 hours, it may be acceptable from a sleep disturbance pointofview to take 22:30to 00:00 hoursand 05:30 to 07:00 hours as the most sensitive periods. In describing noise/vibration climates, the Department of the Environment's Report of the Noise Working Party 1990 [21 defined the period 07:00 to 19:00 hours as 'daytime', 19:00 to 23:00 hours as 'evening' and 23:00 to 07:00 hours as 'night-time'. The subsequent publication of the Departmentof the Environment's Planning Policy Guidance (PPG 24) Planning and Noise [3] recommends the period 07:00 to 23:00 hours as daytime when considering the impact of general noise levels on

area. A small housing development affected only by a single industrial noise source known to maintain a continuous noise level may only take 2—3h at one location. The durationofsamples will be dependent on the noise climate; 10—20 mm/h at different locations is normally sufficient. Vibration monitoringwould typically be of short duration since it is normally only the effectofvibration on the proposeddevelopment that is of interest. Thus measurements only need to take account of the maximum levels that would occur during, for example, train pass-bys or quarryblasting and the number ofoccurrences in a given period. Weather

The preferred monitoring conditions are on a dry and clear day or night with a light wind blowing from the source towards the measurement location, or when it is calm. If the monitoringperiods are over a long duration then the effect of weather should not be important, dwellings. The durationof the survey will be dependent not only provided reasonably accurate information relatingto the on the hours of operation but also on the site of a weather can be obtained, and it will only be necessary to development and/or the noise-sensitiveareas andasurvey avoid long spells ofwindy and rainy weather. carried out over a numberofdays would average out any High winds and heavy precipitation must be avoided differences occurring due to weather conditions. For during surveys. High or even moderate winds result in example, to establish the existing noise climate for a increased background noise levels dueto leavesrustlingin development on the scale of the ChannelTunnel Project trees or hedges and wind noise in fences. Even with a [41! required monitoring twice per year over a 2-week windshield, there can be wind 'roar' effects at the period including weekends at approximately 15—20 loca- microphone itself. Therefore, conditions where wind tions surrounding the proposed Terminal development speeds are greater than 5 rn/s should be avoided. Rain

Environmental acoustics

11

Table 1.1 Measurement units Parameters to be determined Noise source

Noise unit

Other data

Rail

SEL (to determine L&eq)

Road

L

Number and type of trains

LMO, T LAeq, T

L L

(to determineLAeq)

Aircraft

SEL

Industrial

LAeq,T

Traffic counts, light and heavy vehicles Number and types Occurrences of different activitiesand periods of operation

LA9O, T

LApeak (if impulsive)

Construction

LACq, T

LAI,T UK:

Occurrences of differentactivitiesand periods and likely duration of events

LAeq,TA-weightedequivalent continuous sound level over

varying with time.

a stated time period, T, the preferred measure of environmental noise

soundlevel exceeded for 90% of a measurement period, T, widelyused as the descriptor ofbackground, or ambient, noise. used for road traffic noise measurement. LAb, TA-weightedsound level exceeded for 10% of a measurement period, for of a measurement used to describe the maximum noise climate. sound level exceeded 1% T; period, LAb, TA-weighted A-weightedmaximum sound level LA9O, T

1

L,.,

USA: LDN Used widelyto assesscommunity noise. To determineLDN, LAeq. Tmustbe monitoredduring both daytime (07:00—22:00

hours) and night time (22:00—07:00hours).

could affect the measurement equipment and would create higher noise levels due to its impact on roofs or trees or causing the surface of a road to become wet (in wet conditions, tyre noise increases). Temperature inversions could also affect monitoring where long distances are involved but it is likely that variations due to wind would have more effect. Reasonably reliable and up-to-date information can always be obtained from regional weather centres. Weather information should always be recorded during any environmental survey and include wind speed and direction, temperature, humidity and cloud cover. Measurement units

The various units and parameters for measuring environmental noise are definedin Chapter5. In undertakingan environmental noise survey the values identified in Table 1.1 shouldbe determinedfor differentnoise sources. The table also suggests additional parameters that should be obtained. Consideration may need to be given to obtaining frequency spectra ofdistinctnoise sources, e.g. industrial plant, for subsequent design development purposes. When the impact of a particular noise source on a development is being assessed in isolation it may be possible to limit the range of parameters measured (see Table 1.1) but since most equipment records the full

range of units, it may be preferredto discount unwanted parameters at a later date. If vibration levels that are to be measured are steady then r.m.s. acceleration and/or r.m.s. velocity should be determined. Where the vibration levels are caused by intermittentor impulsivesources then the peakacceleration and/or peak velocity should be measured. For subsequent analysis, frequency spectra should also be obtained.

Equipment

The basic instrumentation for noise or vibration measurements, together with a checklist of requirements for instrumentation, is given in Table 1.2. Measurement equipment must be regularly calibrated, at least once every 2 years, and this calibration must be traceable via a laboratory accreditedfor testing by the National Measurement Accreditation Service (NAMAS). To determine environmental noise levels, a calibrated sound level meter complying with the requirements of preferably type 1 butatleasttype 2 as given in BS 6698 [5], or BS 5969 [6] should be used. The microphoneselected should always be protected by a windshield and shielded from heavy rain. In additionto usingequipmentcalibrated to a National Standard, the equipment should always be calibrated on site before and after any survey and at the beginning and

Acoustics in the BuiltEnvinmment

12

Table 1.2 Equipment selection Basic instrumentation Noise

Record keepingand reporting

An important part of the survey procedure is to keep records ofall necessary data.This couldincludeatime log

of events, weather information, measurement locations and sample periods, in addition to the measureddata. Data need to be summarized and sound level histoare a good visual method of achieving this. Charts Accelerometer, suitably fixed grams sound/vibration level versus time can also be showing Chargeamplifier useful. The results offrequency analysescan be described Recording device, e.g. meter more effectively on a sound pressure or vibration level versus frequency (octave band or 1/3 octave band) Vibration

Microphone Pre-amplifier Sound level meter Calibrator Windshield

graph.

A report shouldclearly identify the main results of any

If it is necessary to show all results, they can be provided in appendices. During a site survey, the types of environmental noise andvibration that are likely to be encounteredare dueto transportation, construction or industrial sources.A brief description ofeach is given belowwith relevant legislation criteria, suggested methods of prediction and noise control. A flowchart summarizing the process of acoustic appraisal is included in Diagram 1.5. survey.

Requirement checklist A Traceability: has equipment been calibrated for compliance with relevant standards within past 2 years, e.g. BS 6698 or BS 5969 Type 1 or Type 2? B Does equipmentcomply with specifications for required precision/type for measurements needed? C Could equipmentbe used in damp or windy conditions? D Power supply? E Frequency? F Time history?

end ofany tape recording, usinga reference soundsource typically either an electronic calibrator or

—

pistonphone. Where noise levels are being monitored over a long period of time and are therefore unmannedsome of the time, a reliable data logger coupled to a calibrated sound level meter or equivalent is required. Detailed consideration will need to be given to the power supply of long term monitoring equipment, and batteries may need to be regularly changed in colder weather. Where frequency spectra need to be obtained from a steady sound source this can readily be achieved on site usinga filter set coupled to the sound level meter. If the source is intermittent and/or impulsive, it may be necessary to tape record the occurrence for subsequent analysis or to use a Real Time Analyser for on-the-spot analysis.

The tape recorder or other recording device

should be selected so as not to affect the accuracy of the measurements. Tape recordings should ideally be made linearly, i.e. not A-weighted, in order to improve the signal at low frequencies. Vibration levels can be recorded directly onto meters and time history records kept using chart recorders. Any frequency analysis of intermittentand/or impulsive sources ofvibration should be undertakenusingeither a tape recorder, or a real time analyser which ideally has a lower limiting frequency of 1 Hz or below. On-site calibration is normally achieved using an electronic signal, but it is preferable to use an accelerometer calibrator.

Transportation noise Road traffic Noisesources Fighting Noise

in the 1990s [7], an Organisation for Economic Co-operation and Development publication, observes that road traffic noise is a major source of disamenity as between 32% and 80% of OECD populations were exposed to 18-h levels above 55 dBA. Noise sources of individual road vehicles can be basicallybrokendown to power train noise, which include the engine and transmission, and rolling noise, which is due to aerodynamics andtyre/road surface interaction. The effect of speed on the contributionof the power train noise androlling noise to the overall noise level from a single vehicle is shown in Figure 1.2. For light vehicles, engine noise in low gears at low road speeds dominates up to about 30 km/hwhere at higherrevolutions/mm rolling noise starts to become dominant. For heavyvehicles,noise from the diesel engine, exhaust and cooling fans dominatesup to about 50 km/h,before rolling noise becomes asignificant factor. Above50 km/h, rolling noise increases at a rate of about 9 dBA per doubling of speed for all vehicle categories. Thus the noise level due to a single vehicle can be determinedif its speed is known. The noise level due to road traffic with a mixed flow of light andheavy vehicles can be determinedfrom Cakulation ofRoad TrafficNoise [8]. It is basicallydependent on the flow of vehicles during a period of either 1 or 18 h (06:00—24:00

hours), their speed and the proportionof

heavy vehicles. Additional factors are the texture of the road surface which affects rolling noise and the road gradientwhich affects enginenoise. Inwet conditions tyre noise increases; however, road traffic noise assessments assume dry road conditions. In addition to the engine/rolling noise there may be occasions when noise from refrigeration equipment or reversing signals need to be considered. Data for modern

Eiivironmeatal acoustics LIAISON

PLANNING SURVEY

ON SITE

I

13

RESULTS

Diagram 1.5 Summary ofacoustic appraisalprocess refrigerated vehicles, i.e. not diesel engine powered, traffic noise is currently described in terms of LAeq, but it indicates that noise levels from equipmentwould typically has been converted from LAb levels. For most situations: LAeq,T LAb,T— dB. In 95% of be 65dBA at lOm. suchconversions the estimated LAeq,TLSlikelyto be within Measurement unit ±2dB of the 'true' value.

The measurementunit that has historically been used to described road traffic noise is LAb. LAb is the A-weighted soundlevelwhich is exceeded for 10% ofthe time period. The period normally used is 18h (06:00—24:00 hours). The LAb,18 h noise level is the basis for determining eligibility under the Noise Insulation Regulations 1975 (see Legislation and criteria, below) [9]. LAeq, Tis the preferredunit formeasuring environmental noise generally and is the A-weighted equivalent continuous sound level. However,in manyinstances, road

3.axl, commercial v,hicl.s

3. axlecommercial vehidex 2- axle commercial vel,icles

E

N

Busesand coaches

2- axle commercialv.hlc*es

OOkg u.w.

>

litvse

Private cars and

0 C a-

S,eed(km/hI

Figure 1.2 Generalizedsound level/speedcharacteristicsfor different vehiclecategories

Legislation and criteria

In the UK, the main legislation dealingwith road traffic

noise is the Noise Insulation Regulations 1975 [9]. This is issued under the Land Compensation Act 1973 [10]. These regulations were brought into force to compensate residents subjected to additional noise due to the use of new roads. Road construction noise is also included. If additional noise is at or above a specifiedlevel the affected residents receive a grant for acoustic double windows, supplementary ventilation, and, where appropriate,venetian blinds to control solar gain in south-facingwindows, anddouble orinsulated doors. The specifiedlevel is 68dB LA10 b8h These regulations do not apply to new housing. New housing or development should be appraised by PPG 24 [3]. The guidance proposes the followingnoise exposure categories (NECs) based on a 15-years-ahead predicted traffic flow: NEC D Planningpermission shouldnormally be refused where externalfree-fieldnoise levels are in excess of 72dB LAeq (07:00—23:00hours), or 66dB LAeq (23:00—07:00hours) NEC C Planning permission should not normally be grantedwhere external free-field noise levels are in excess of 63dB LAeq (07:00—23:00hours), or 57dB LAeq (23:00—07:00hours) but less than those in NEC D.

14

Acoustics in the Built Environment

Where it is considered that permission should be

given then conditions requiringadequate protection against noise should be imposed. NEC B Noise should be taken into accountwhen determining planningapplications and, where appropriate, conditions requiringadequate noise protection should be imposed where external free-field noise levels are in excess of 55dB LAeq (07:00—23:00hours) or 45dB LAeq (23:00—07:00) hours butless than those in NEC C. NEC A Noise need not be considered as a determining factor in granting planning permission where externalfree-field noise levels are below 55dB LAeq (07:00—23:00hours) and 45dB LAeq (23:00—07:00hours) However, noise levels just below these limits should not be regardedas desirable. For dwellingswith windowsopen for ventilation the noise levelsin NECA indicate that 45dBLAeq is acceptable internally during the day and 35 dB LAeq at night. There are no regulations governing acceptable noise levels in offices. However,BS 8233 [11] suggests that for private offices 40—45 dB LAeq,- and in open-plan areas 45—50 dB LAeq, T should be the aim. This indicates that where external noise levels are in excess of60dB LAeq or 63dB LAb, then a sealed office building with some form of mechanical ventilation is likelyto be required. Prediction

An accurate procedurefor the prediction of noise due to freely-flowing road traffic is given by Calculation of Road Stage 5 — Combine contributionsfrom all seaments

Table 1.3 Typical road traffic noise levels based on BS 8233 Situation

At 20 rn from the edge of a busy motorway carryingmany heavy vehicles,average traffic speed 100rn/h, interveningground

LAiO, 18h

LAeq, 16h

80

78

grassed

At 20m from the edge of a busy main road through a residential area, average traffic speed 50 rn/h, intervening ground paved On a residential road parallel to a busy main road and screenedby the houses from the main road traffic

70

68

60

58

Diagram 1.6 Flow chartforpredicting noisefrom road schemes

Traffic Noise (CORTN) [8]. To determine noise levels in accordance with CORTN, it is necessary to know detailed information about the road geometry andsurface, topographyand likelyfuturetraffic parameters. The traffic flow 15 years after the date of interest should be considered. Depending on the road geometry and topography, the road is brokendown into segments and the resultantnoise level at a reception point is calculated for each segment and then combined to give an overall level. A flowchart showing the process is shown in Diagram 1.6. This calculation method is available as a computer program such as RoadNoise by W. S. Atkins & Partners (Epsom, Surrey) or HFA Noise by Halcrow Fox (London), and a large number of acoustic consultants have their own inhouse programs. Table 1.3 taken from BS 8233 gives an indication of traffic noise levels fordifferentroad types.Figure 1.3 from

Environmental acousbcs

15

90

......

85 -

80-

..

-C

. .

.

.

j75 70 a)

-> a

. .

65

.

I:: 50

I

10

I

50

500

100

Iii

I

5000 10000

1000

TRAFFIC FLOW, VEHICLES PER HOUR

Figure 1.3 Mixedflow road traffic noise at 10m (based on Reference 8)

20 ILLUMINATED ZONE

0

SHADOW ZONE

15

Diffracting edge

C

0 0

Illuminated zone

Effectiv

10

——

--

Shadow

—

b

zone R

(

8=a+b—c

5

0

1.0

0

1.0

2.0

Reception

point

3.0

Path difference, (m)

Figure 1.4 Barrierattenuation for road traffic noise [8]

CORTN gives the basic noise level at 10m from the nearside carriageway edge for traffic containing about 10% heavygoods vehicles (those over 1.5 tonnes) at up to 60km/h. This also assumes that the road surface is bitumenandrelativelylevel (gradient less than 3%). Ifthe traffic speed exceeds 60 km/h then the noise level will increase at a rate of approximately 6dBA/doubling of speed. If the percentageof heavyvehicles is greater than 10% then an approximate factor of 2dBA/doubling of heavyvehicle content could be used.

The propagation of traffic noise with distance is predominantly based on distance to the source, angle of view of the road, interveningground cover, andwhether any barriers exist between source and receiver. Typically, over ground covered with vegetation and a reception point not more than 4m above ground, the reduction in noise level could be as much as 7 dBA/doubling of distance. Over hard ground or an acoustically reflective surface such as concrete or water, the reduction in noise level will be 3 dBA/doubling of distance.

16

Acoustics

in the Built Ezivironment

100

95-

90-

Heavy vehicles

75 70 65 60 20

40

80

60

100

120

Speed (km/h)

Figure 1.5 Single-event road vehicle noise level at d!fferentspeeds

D a) > a) a) U, U)

a)

-D C

0

U)

at a distance of10m [12]

100 95 90 85 80 75 70 65 60 55

50

63

125

250

500

1000

2000

4000

8000

Octave band centre frequency (Hz) Interrupted flow

Free flowing

Figure 1.6 Frequency spectrafor dfferent road traffic flow conditions equivalent to 76dB LAb, 7-

The effect of barriers depends on the path difference Figure 1.5 provides an estimate of the single-event and it is importantto checkthat the line ofsight between exposure level at a distance of 10 m for light and heavy source, 0.5m above road surface, and receiver, typically vehicles for different speeds. This can be used to 1.5 m or 4.0 m above ground (ground and first floor determinethe overall noise level in terms of LAeq at 10m reception heights respectively) cuts the barrier (Figure for a number of vehicles. The overall level at a distance 1.4). The sourcefor light and mixed traffic is taken to be greater than lOm can then be estimated based on 0.5 m above the road surface, and for heavy vehiclesonly attenuation of 3—7dBA/doubling of distance depending can be taken to be typically 1.5m above the road surface. on the ground cover. There are also occasions when a The barrierneedsto extendasignificantway alongside the predictive exercise may become complicated anda measroad to provideeffective screening but if this is achieved urementis the only availablecourse ofaction, suchas at a the reduction canbe determinedfrom Figure 1.4. traffic-lightedjunction or a roundabout. The resultant noise levelsare normally given in terms of Alternatively,ifvehicle flows are low and measurements difficult to make, it maybe preferable to use the following a level at a particular point. However, provision of method based on the Noise Advisory Council guidance contours, particularlyon a site where the best location for [12]. a building is being determined, can be helpful. The

Environmental acoustics

17

100

V a)

> a,

0 E

E

60 50

100

150

200

Speed (km/h)

Figure 1.7 Noiselevels ofpassenger trains at dfferentspeeds

at 25m [14]

predicted levels for road traffic noise will be overall speeds get higher, aerodynamic noise may become sigA-weighted single figures which can be converted to nificant, but that stage has not yet been reached in the typical octave band levels using the graphs shown in UK Figure 1.6. Measurement unit Train noise is measured in terms of the A-weighted Railways Noise sources equivalent continuous noise level,LAeq,T Although in the The predominantsources ofnoise dueto train movement past the period T has been taken as the full 24-h daily are propulsion equipment and wheel/rail interaction. period for railway noise, The NoiseInsulation(Railways and The propulsion equipment includes diesel locomotives Other Guided Transport Systems) Regulations 1995 [15] anddiesel multiple units; noise from electric locomotives identif' the daytime (06:00—24:00hours) and night-time andelectric multiple units is significantlylower than from (00:00—06:00hours) periods. PPG 24:1994 [3] identifies diesel equivalents. In addition, auxiliary equipment,such the daytime (07:00—23:00 hours) and night-time asventilation systems and othercarriage-mounted compo- (23:00—07:00hours) periods. nents, can be sources of noise, and elevated structures, In order to determinethe LAeqovera given time period, such as bridges, tend to increase noise levels but both are it is often preferred to undertake a calculation using typically insignificant in the UK compared to diesel individual train pass-by levels. Thus the sound exposure locomotive and wheel/rail noise. In the US there are level (SEL) is measured for different train types; typically many steelelevated structures causing high noise levels. A this is at a distance of 25m. In addition, the maximum similar situation also occurswith Docklands LightRailway noise level is often measuredin order to assess the effect but it is predominantly at low frequencies [13]. The of train pass-bys on conversation and telephone use, for maximum noise level at 25 m from diesel locomotives is example. typically85—95dBA [14]. Wheel/railnoise is due to the vibration ofboth caused Legislation and criteria by the action of one rolling over the other. The para- The Railway Noise Insulation Regulations [15] operate on meters that can affect this noise are the type of track, i.e. a similar basis to the Noise Insulation Regulations [9] for continuously welded rail (CWR) orjointed (+5 dBA), the road traffic noise. The specified levels are 68 dB LAeq 18h type of braking system, i.e. disc- or tread-braked, and (day time) and 63dB LAeq6h (night time). If new or maintenance of track/wheels, i.e. removal of corruga- additionalrailway noise togetherwith railway noise in the tions. Noise due to tread-braked rolling stock can be vicinity is at or greater than these specified levels at the 10dBA higher than disc-braked, and badly corrugated facade ofa dwelling, the residents are entitled to a grant track could cause increases of 10 dBA. Therefore rolling for noise insulation to habitable rooms. The noise stock with discbrakes on CWRthat is regularly maintained insulation grant is for acoustic double windows, supplewill result in the lowestnoise levels. Typical noise levels of mentary ventilation and, where appropriate, venetian the different train types hauledby electric locomotivesare blinds to control solar gain in south-facingwindows, and shown in Figure 1.7. Noise control measures to railways double or insulated doors. are being brought in, in the form of 'Hush' rails, The Regulations are based on the findings of the beneficial through their smaller cross section, and wheels DepartmentofTransport's Railway Noise and the Insulation which are damped to reduce 'ringing'. In future, as train ofDwellings [16]. These Regulations do not apply to new

18

Acoustics in the Buift Environment

-6

25

100

50

150

200

Distancefrom train (m)

Figure 1.8 Attenuation oftrain noise with distance over grassland [14] housing; PPG 24 proposes the following noise exposure categories. NEC D Planningpermission should normally be refused whereexternal free-fieldnoise levels are in excess of 74dB LAeq (07:00—23:00 hours) or 66dB LAeq (23:00—07:00hours) NEC C Planning permission should not normally be granted where externalfree-field noise levels are in excess of 66dB LAeq (07:00—23:00hours) or 59dB LAeq (23:00—07:00hours) butless than those in NEC D, or where individual noise events regularly exceed 82dB (maximum SPL on 'slow' meter setting) at night. NEC B Noise should be taken into accountwhen determining planning applications and appropriate conditions requiring adequate noise protection should be imposed where external free-field noise levels are in excess of 55dB LAeq (07:00—23:00hours) or 45dB LAeq (23:00—07:00hours) but less than those in NEC C. NEC A Noise need not be considered as a determining factor in granting planning permission where externalfree-field noise levels are below 55dB LAeq (07:00—23:00hours) and 45dB LAeq (23:00—07:00hours) However, noise at the high end should not be regardedas desirable. For dwellingswith windowsopen for ventilation the noise levels in NECA indicate that 45 dB LAeq is acceptable internally during the day and35 dB LAeq at night.

suggested in guidance given by the US Environmental Agency [17]. This relates to an external free-field noise level of 65—70 dBA unless it is a sealed building. Prediction

Procedures for calculating noise from trains are given in the Department of Transport's Calculation of Railway Noise 1995 [18]. This calculation method requires the number and types of trains in an 18-h daytime or 6-h night-time period. Typical sound exposure levels, SEL, for a variety of train types are given where measured data is not available. In addition the type of track and any bridges or viaducts crossed by the rail and the topography need to be known. The railway is then broken down into segments, where necessary, and an overall noise level is determined for a reception point. The process is shown in Diagram 1.7. The overall LAeq noise level on a specific site can be determined from the sound exposure levels (SEL), as described in Chapter 5. In order to assess noise levels at other distances over grassland, the chart shown in Figure 1.8 can be used. Typically this is 5dBA/doubling of distance. Intervening properties such as semi-detached and terraced housing could provide the following noise reduction: single row of semi-detached houses 8 dBA subsequent rows, each 4dBA terraced housing 13dBA

• • •

Cuttings orinterveningground barrierscould be assessed in a similar way to that described for roads. These procedures can also be used to determinethe 07:00—23:00 and 23:00—07:00h period noise levels for PPG 24 assessments. Although the barrier corrections for railways are slightlygreater, see Calculation ofRailway Noise, the barrier attenuation in Figure 1.4 can be used. BS 8233 [11] Fordevelopments with generalofficeswhere the impact contains estimated noise levels for a track carrying dieselon communication, either verbal or by telephone, must be hauledpassengers andfreighttrains at differentdistances considered, a maximum internal level of 55—60 dBA is over open grassland andis reproducedhere asTable 1.4.

Environmental acoustics

19

STAGE 1 — Divide railway into segments

STAGE 2 — Reference Noise Level (SELREF)

No. of vehicles correction Track/supportstructure correction

}

For each segment calculatethe reference noise level (SELl for each train type on each track

STAGE 3 — Propagation Distance correction

Air absorption correction Ground correction Ballastcorrection

A

Screening correction

For each segment determine

Angle of viewcorrection

the correction factors for each train type at the receiver position for each track

STAGE 4 — Reflectioneffect Facade correction Reflectioncorrection

STAGE 5 — Convert SEL to LAeq Correction for time period Correction for number of trains

}

each track

Repeat calculation

there any

each

}

No STAGE 6— Calculatethe total LAeq for the railway

for each segment

LA8qS

for

segment

more segments?

For each time period combine the

For each segment calculateSEL at reception point and convert SEL to LAeqfor each train typeon

Sum LAeq to obtain predicted level from railway

Diagram 1.7 Flow diagram for the calculation ofnoisefrom railways Table 1.4 Noise levelsfor a typical railway' Distancefrom track over open grassland (m)

25 50 100 200

LAe9,18 h

(1B)

67 64 59

54

on BS 8233. Typical railway traffic is assumed to consist of a mixture ofa total of90 high-speed diesel-hauled aBased

passenger and freight trains, per 18h day (06:00—24:00hours).

The typical octave frequency band levels can be determined either from on-site measurements or the typical noise spectra given in Figure 1.9a and b for both diesel electric locomotives and tread- or disc-braked rolling stock hauled by electrically-poweredlocomotives. Aircraft

Sourcenoise

The main concern relating to aircraft noise is associated with take-offs and landings near an airport. In addition, ground operation noise may also need to be considered. In termsofnoise dueto flying operations, the mainfactor is the type of aircraft. The maximum noise levels for various types of aircraft under different operating condi-

20

in the Built Environment

Acoustics

Planning guidance andcriteria PPG 24 [3] identifies the following noise exposure categories for aircraftaffecting new dwellings.

100

95 90 85 80

63

260

linE 500

1000

2000

4000

8000

Octave band centre frequency (Hz)

H

100

f

95 90 85 80 75 70 65 60 56 50

63

125

itii 250

500

1000

2000

4000

8000

Octavebandcentrefrequency (Hz)

Ib)

:::

8580'-

I

t5Li 63

c)

125

I!IiI 250

Octave

600

1000

bandcentrefrequency

2000

4000

8000

Ha)

a

Figure 1.9 Frequency spectrafor trains: (a) diesel locomotive at 25 m; (b) tread-brakedpassenger train at 25m with electric locomotive at 100km/h; (c) disc-braked passenger train at 25 m with electric locomotive at 100km/h

NEC D Planningpermission should normally be refused where externalfree-field noise levels are in excess

of

72 dB LAeq (07:00—23:00hours)

or 66 dB LAeq (23:00—07:00hours) NEC C Planning permission should not normally be grantedwhereexternalfree-field noise levels are in excess of 66 dB LAeq (07:00—23:00hours)

or 57dB LAeq (23:00—07:00hours) butless than those in NEC D, orwhereindividual noise events regularly exceed 82dB at night. NEC B Noise should be taken into account when determining planningapplications and, where appropriate, conditions requiringadequate noise protection should be imposed where external free-field noise levels are in excess of 57dB LAeq (07:00—23:00hours) or 48 dB LAeq (23:00—07:00 hours) but less than those in NEC C. NEC A Noise need not be considered as a determining factor in granting planning permission where externalfree-field noise levels are below 57dB LAeq (07:00—23:00hours) and 48dB LAeq (23:00—07:00hours) However, noise levels just below these limits should not be regardedas desirable. For dwellingswith windowsopen for ventilation the noise levelsin NECA indicate that 45dB LAeq is acceptable internally during the day and35dB LAeq at night.

There are a number of airport grant schemes under which grantsare paid towardsthe cost ofsound insulation in existing dwellings within defined areas around major airports. The sound insulation package is similar to that offered under the Noise Insulation Regulations [9] for road traffic noise, plus increased roofinsulation.

dons are given in Table 1.5. Data are given for the UK reference distance of 152m used to determine the Reference Noise Level. Military airfields may also need to be considered not only for noise near the airfield but Prediction sometimes due to other operations suchas lowflying.Data Although a simple calculation can be carried out using in this case needs to be obtained from the Ministry of the sound source data (SEL) from Table 1.5, the number Defence. of aircrafttypes and a correctionfor distance, the error in accuracy is likely to be great. In reducing the error, Measurement units reliance will have to be placed on published contour Historically,the Noise and NumberIndex (NNI) has been maps which are based on accurate flight profile data. used as the noise unit for measuring aircraft noise. It takes However, consideration may need to be given to the into accountthe maximum perceived noise level of each maximum noise level on a site from a design point of aircraftfor the number of aircraft movements during a view. Measurement is obviously the easiest method of 12-h period (06:00—18:00 hours). However, in September determining maximum noise levels, but if this is not 1990 the Departmentof Transportchangedto the use of possible, then the maximum noise level at a particular location can be obtained by calculating the slant distance LAeq to describe aircraft noise over a 16-h period as shown in Figure 1.10 and applying the correction (07:00—23:00 hours).

EnnthI acoustics Table 1.5

Typical noise levels ofaircraft

at a distance of152 m

Aircraft type

Example

Operation

Supersonic long range

Concorde

Take-off

126 116 107

Departure Approach

Old technology long range Old technologyjet

B707 DC-8 VC-10

Approach

Trident

Take-off

B727 B737

Departure

Take-off

112—120 105—112 99—102

120

113—115

Approach

111—115 107—110 94—99

Take-off Departure Approach

103—107 99—104 91—96

110 108

Departure

BAe1-11

SEL (dBA)

(dB)

107

97—100

DC-9

New technology longrange

B747 DC 10-30

New technology medium range

Tristar

Take-off

B737-300 B757

Departure Approach

DC1O-10

97

96—104 93—100 85—92

B767-200

New technology feeder/commuter Hushedjet

BAe146-100/200

Take-off

BAe1-11

Departure Approach Take-off

400/500

Departure

92 87 85 108—110 102—106 91—93

Approach

STOL medium/large

Dash 7

STOL small

Twin Otter

Take-off Departure Approach Take-off Departure Approach

82 79 73—78

91 80 76

Table 1.6 Frequencyspectrafor typicaljet aircraft movements at approximatelySmfrom ailport Octave band centrefrequency

Take-off:

96dBA

Landing: 89dBA

63Hz

125Hz

250Hz

500Hz

1 kffz

2 kHz

4 kHz

8 kffz

92 79

94

96 86

95 84

92 82

84 83

68 80

56

85

71

dB dB

8 dB/doubling of distance. An indication of the fre- NNI contours are available it is possible to estimate the quency content for typical jet aircraft types is shown in approximate equivalent LAeq 16 h value within ±2dB from Table 1.6. the following table: contour are available from the Civil Aviation maps LAeq NNI 35 40 45 50 55 60 Authority or via the local authority or airportauthorities; examples are Gatwick, Heathrowand Manchester. If only LAeq, 16h 57 60 63 66 69 72

22

Acoustics

in the Built Environment FIightpah of aircraft

Actual distance to aircraft

d=V h2+O

0 Reception point

Figure 1.10 Estimation ofslant distancefrom an aircraft flightpath

Ground operation noise can be taken to be approximately 85 dBAat 300 m andto reduceat a rate of 12 dBA/ doubling of distance.

Control oftransportationnoise sources

Unless a newtransportation route is under discussion, the design of the route cannot be influenced and noise control can only be achieved by increasing the sound

insulation of the building under consideration or by the introductionof a noise barrier. The introductionof noise barriersin the case ofaircraft noise where ground running is a potential problem will only be of limited benefit if the development is near an airfield. Appropriate mufflers or noise testing pens/hush houses will be needed to control noise from engine testing. A noise barrier should ideallybe located as close to the noise source as possible. In some cases this may lead to maintenance problems since it may need to be sited on someone else's land. For the determination of the preferred location for a noise barrier, if it cannot be positioned close to the source, sections across the site will be invaluable. Using a sight line between the source height, for example for roads it will be 0.5 m above the road surface, and the reception point, typically at a window on the highest floor of a building, the most effective position of a barrier can be decided upon. The performanceofa noise barrieris given by the path length difference as illustrated in Figure 1.4 forroad traffic noise. In order to takeaccountofthe differentfrequency spectra oftrain noise comparedto trafficnoise,Figure 1.11 canbe used. The noise reduction achieved by a noise barrier along a road or railway is typically between 5 and 10dBA and to achieve greater reductions is often quite difficult. The effect of excess attenuation due to soft ground, which was probably included in determining

SHADED AREA — PREDICTED BARRIER ATTENUATIONS UNLIKELY TO BE REALIZED IN PRACTICE

I

N

>-

0 z w ci w

U-

0 (b)

Figure 1.11

0.5

1.0

1.5

PATH DIFFERENCE(m)

(a) Path dfference; (b) attenuation provided by noise barriers at dfferentfrequencies

2.0

Environmental acoustics

Table 1.7 Typical construction plant noise Equipment

Tracked loader Tracked excavator Dozer Piling: Diesel hammer Drophammer + wooden dolly

Augerbored

Pneumatic breaker Concrete pump Truck mixer Concrete mixer Batching plant Poker vibrators plus compressors Compressors:

4m3/s 7m3/s

Approx.

'eq

109 109 111

130 115 112 116 110 110

95 105 102

98 101 111

23

In addition to the above equipmentwhich is operating normally out in the open, structureborne noise due to drills or breakers maycause potentialnoise (dB) hand-operated in problems buildings coupled to the construction under consideration. The noise level due to structureborne noise varies significantly depending on local site conditions and an estimate of the noise level likely to occur cannot easily be provided, although noise levels of 55—60 dBA in nearby areas during percussive drilling could be anticipated. Measurement unit The A-weighted equivalent continuous sound level,

is the preferred unit for describing construction LAeq, noise. However, in addition, to take account of isolated events and impulsive sources such as piling, it is recommended that the maximum noise level, is also considered.In describing site noise, the particularperiod of the day should always be stated. Legislation and criteria

Generator

104

Noise from construction sites is specificallyreferred to in Sections 60 and 61 of Part III ofthe Control of Pollution Act 1974 [19].

Pump Crane

103 103

Section 60

17m3/s

Under Section 60 ofthe Act, a local authority may serve a Notice on the contractor specifyingone or more of the following:

• • •

plant or machinery which is, or is not, to be used the noise level on site from transport, is negated in hours during which works may be carried out determining the overall performance provided by a noise limits unless it is on earth barrier, mounding with shallowsloped sides. The design of the barrier should ensure However, in specifyingany of the above, a local authority that the length of the barrier is sufficient to protect the should have regard to: whole development. relevant Codes of Practice issued under this part of The barrier need only be relatively lightweight and the Act, viz. BS 5228: Parts 1—4 [201; normally a close-boarded timber fence is quite adequate. the need to ensure that the best practicable means Other barrier types include metal sandwich construction ('practicable' meaningreasonably practicable having or precast concreteunit assemblies. The performanceof regardamongstother things to local conditions, the barriersalongside railways can be reduced by as much as current state of technical knowledge, and the finan5 dBA where the side closest to the track is acoustically cial implications; 'means' includes design, mainreflective.Consideration shouldbe given to a barrier type tenance and manner and periods of operation of with an acoustically-absorbentsurface facing the track. plant and machinery and the design, construction There are barriers, of metal sandwich construction and and maintenance of buildings and acoustic strucprecast concrete faced with woodwool slabs, which will tures; this is provided safety and safe working achieve this requirement. conditions are met and regard paid to any provision of BS 5228) are employed to minimize noise; the interest of the recipient before specifying any Construction noise particular methods or plant or machinery, i.e. where alternative methods or plant more acceptable to the Sources construction operatorwould be substantiallyas effecMajor noise sources involved with construction activities tive in minimizing noise as those proposed by the include pilingrigs, earthmoving equipment suchas dozers local authority; and excavators, and concrete pouring plant such as the need to protect any personsfrom the effect of concrete pumps and truck mixers. A range of construcnoise. tion equipment is given in Table 1.7 which includes the approximateaveragesoundpower level during the activity Any person served with such a notice may appeal to a of each item. In most cases, diesel engine noise predom- magistrate's court within 21 days from The inates but consideration needs to be given to piling and grounds for appeal and form of notices arereceipt. outlined in material handlingnoise. Departmentof the Environment's Circular 2/76 [21].

• •

• •

24

Acoustics

in the Built Environment

Section 61

The other approach, outlined in Section 61 of the Act, places the onus on the contractor or other responsible persons. In this section, the contractorcan notif'the local authority of his methods of working and noise control procedures, and apply for a consent. The local authority may grant such a consent or have the power to apply conditions to the consent. Thus the contractors can have some certainty about their position and the risk of interruptionto worksthat have started is removed as far as possible. The local authority should reply to applications for consentwithin 28 days. Ifthis reply is not forthcoming, or the conditions attached are not acceptable, the contractor can appeal to a magistrate's court within 21 days from the endofthatperiod. Applicationsfor consent should be made at the same time as or, where it is necessary, after application for Building Regulations approval. However, this couldhave certain implications on normal tendering procedures, and it is being suggested that local authorities shouldbe preparedto giveadvice as early as possible in respect of their proposed noise limitations. It is essential to the working ofthis legislation forboth contractors and local authorities to have consultation prior to any formal procedures occurring. Contravention

If the contractor or other responsible person knowingly allows work to be carried out, in contravention of either any conditions attachedto a consentor any requirements of a notice, theywill be guiltyofan offence against Part III of the Control ofPollution Act.Itshouldbe noted that the contractorwould also be responsible for a subcontractor operating on the project and their attention must be drawn to any requirements of a consent or notice on that project. Code ofPractice

The relevant Code of Practice relating to construction noise is BS 5228. The aim of the Code is to recommend methods of noise control in respect of construction and other open sites and to enable developers, architects, engineers, planners, designers, site operators and local authorities to control noise. One of the factors which complicates any assessment is the relative sensitivity of different individuals in the same neighbourhood to the

same noise. Site noise is normally described in terms of the equivalent continuous A-weightedsound level LAeq over a stated time, for example 1 h or 12 h. In addition to LAeq, the site noise may be described in terms ofthe maximum sound level, or the one-percentile level LA1. Whichever measure is selected to describethe site noise, the period of the day to which the particularvalue ofthe measureapplies must also be stated. In assessingwhether noise from a site is likely to constitute a problem, in addition to site location and the existing ambient noise levels, consideration should be given to the following:

•

• Hours of work: certain periods of the day are more indicationof the differthan others; as an encebetween daytime andevening time working, the noise level mayhave to be up to 10 dBAquieterin the evening. Even during the daytime period, certain times are likely to be more sensitive than others in offices andother workplaces. The code states that at noise sensitive premises the LAeq may need to be as low as 40—45 dBA during night-time. It is possible, however, that the level may need to be even lower to sensitive

disturbance.

sleep • avoid Attitude of site operator: noise from the site may be is all

•

more readily accepted ifthe siteoperator doing he can to avoid unnecessary noise. The acceptability of the projectitselfmay also be a significant factor. Noise characteristics:impulse or tonal characteristics may make the site noise less acceptable. There is no detailed information available on assessing the acceptability ofsite noise.

Construction site noiseprediction

Once a practical noise limit has been specified by the local authority, it will be necessary for that local authority and also the developer, architect, engineer and contractor to know whether the intended site operations will cause problems. The noise levels for different operations will have to be predicted at tender stage so that appropriate allowancescan be made in the tender for noise control. Once those site operations that exceedthe noise limitare known, the contractorwill be required to include for the necessary noise control to achieve the limit. The noise limitwould normally be quotedas a site boundarylevel in terms of LAeq over a given time period, typically a 12-h working day, and/or in terms ofeither an overriding short period, e.g. 5 mm, or maximum levels measuredwith a sound level meter set at slow or fast response. In order to estimate the noise level at a given location, the procedurebasicallyconsists of the followingfactors: sound power outputs of processes and plant distances from source to receiver presence of screening by barriers and the reflection of sound periods of operation of processes and plant. Anexample ofthe dataneeded is shownin Table 1.8. In this case the LAeq, 12h level would be:

• • • •

LAeq, 12 h

= 10 log2[4 X 10'° + 1 X 10° + 8 X 10'0 + 6 X 10'°] = 73dB (to the nearestdB).

The method of prediction can be represented by a diagram takenfrom BS 5228,reproducedhere as Diagram 1.8.

Setting suitablecriteria

Information from local authorities in the UK indicates that noise from road-works,andconstruction and demoliDuration of site operations: higher noise levels may tion sites causes relativelyfew cases of noise nuisance, i.e. be accepted by local residents provided they are between 5 and 10% of the total nuisances confirmed. aware that the work is only of short duration; good However,the effectofconstruction site noise as a possible nuisance must not be overlooked. There are three public relations are importantin this.

25

Environniental acoustics

Table 1.8 Example of construction site noiseprediction based on BS 5228 [2011 Operating soundpower 'WAeq (dB)

Distance (m)

100 116 109

50 50 30

109

15

level,

Plant and size

Resultant

Compressor 7m3/min Pneumatic breaker Tracked excavator Tracked loader

in 12 h

(dB)

(dB)

(h)

42 42 38 32

0 5

0 0

58 69

4

0 4

71

8 6

nuisance arise dealing Section 58 or Section 60 of the Control of Pollution Act. Although construction noise nuisance should be dealt with under Sections 60 or 61, individuals may complain to local authorities, who could then serve a Notice under the Environmental Protection Act to abate the nuisance.

0 0

73

Although there is no requirementto set a noise limitfor any ofthe three approaches, noise limits can be set based on those aspectsdescribed earlierin the 'Code ofPractice'

section above. Noise nuisance caused byconstruction noise is normally ofshort duration.Often, there are no means availableto apply control, e.g. structurebornenoise due to hand-held tools, and so it is very important that the contractorhas a good public relations policy. If a noisy activity has to take place which could affect neighbouring properties, the neighbours should be warned, particularly with regard to the durationofthe activity. Itmay evenbe possibleto agree to periodsofoperationthat are acceptable to both parties.

STATIONARY PLANT

MOBILE PLANT

Plant LWA

On site

I

Correct for distance and allowfor and reflection

Select LWA for mobile plant

Correct for minimum distance between plant and assessment location. Allow for screeningand reflection Calculate LAeq from haul road

creening

Combine levels with percentage on-time

On haul road

I

Select LWA for stationary plant and obtain on-time at maximum level

Correct for actual distance and allowfor screeningand reflection

level

Screening attenuation (dB)

• encourageapplication for prior consent • serve a Notice andif any cases ofnoise • allow work to be carried out with them either under

Select LAeq at lOm distance

On-time

correction

Distance attenuation (dB)

different approaches available to local authorities in dealing with construction noise:

Activity LAeq

soundpower

Mobileplant

assessment

Estimate distance ratio and correct for equivalent on-time

______________ Estimate the on-time for each

allowing for screening and reflection

activityduring the _____________ period of assessmentand applycorrection Calculate combined LAeq

Diagram 1.8 Predictionofsite noise (afterBS 5228: Part 1) [2011

I

26

Acoustics in the Built Environment

preferred by both authorities and site operators because Noise from construction equipment can be controlled at specified requirements can be easily monitored. source or by controlling the way it propagates or spreads. Controlat source is by: Noise control

• Substztution. Noisy plant and operations including

Industrial noise Noise sources

piling should be replaced by less noisy alternatives Industrial noise is caused where reasonably practical. by a wide variety of sources. Some • Mod?fication. Machines can be made quieter by other general noise-producing activities are quarrying or mineral extraction, material handling, metal fabrimodification, but this should only be carried out cation, and building services plant operation. after consultation with the manufacturers. The situations and modes of operation of the sources Enclosuresand screening. In designing an enclosure to can also vary widely, and it can be a single machine or an control noise from a machine, consideration must be of machines, operating either internally within a array given to the ventilation requirements in order to or externally,which are ofconcern.The sources building prevent overheating. Suitable materials and some even emit noise levels which fluctuate with time, for examples ofenclosure design are included in BS 5228. may mobile plant, machines on- and off-load. ExamAlternatively,screens around the noisy area can be example used or, if screening cannot be provided by site ples of the various types of industrial noise sources are: mineralextraction: blasting and mobile earthmoving buildings or by earth mounds, temporaryscreening can be constructed with materials such as externaltype equipment with reversing signals, truck

•

•

quality

or

woodwoolslabs.

prescreeded • Use andplywood siting of equipment. Plant should be used in

• •

accordance with the manufacturer's instructions. In situations where operation is intermittent, plant should be shut down or throttled down to a minimumwhen not in operation. Care should be taken to position noisy equipment away from noise-sensitive areas, and in caseswhere an item ofplantis known to emit noise strongly in one direction, it should be orientated so that the noise is directed away from noise-sensitive areas. Engine covers should be kept closed during use. Maintenance. Regular and effective maintenance of plant is essential and will assistin keeping noise levels to a level similar to that from a newitem of plant. It is particularly important to effectively maintain the silencing systems, for example engine exhaust silencers. Periods of use. It may be possible to operate certain items of noisy equipment to avoid sensitive periods. In some cityareas, agreements have been reachedfor piling not to take place during the periods 10:00—12:00 hours and 14:00—16:00 hours, thus enablingnormal officeactivitiesto take place during these hours for a limited period without any likelihood of disturbance.

Prajectsuperthion Noise control should be considered at each project stage in order to meet the necessary requirements. Early consultation between developer, architect or engineer, and the local authority should be held to ascertain the likely noise limitations. Processesandequipmentinvolved with the site operations should be considered in order to keep those particular noisy operations to a minimum. Issues include planningthe hours ofworking, ensuring the use of the most suitable plant, economy and speed of operations, on-site monitoring, and the provision of prominentwarning notices where high noise levels exist. Local authorities may wish to lay down requirements relating to the work programmes, plant to be used, siting of plant, and working hours, rather than (or in addition to) specifyingsitenoise limits. This approachwill often be

• loading; materials handling: fork lifts or cranes, loading/ •

unloadingtruckswith associated impact noise which can take place internally or externally; metal fabrication: cuttingof steel sheet by guillotine, press operation and associated material handling including wastedisposal into bins possiblyvia cyclone

• units; building services plant operation: this could serve an office or

building industrial premises with the plant sometimes mounted on the roof.

Due to the varietyofsources, typicalnoise levelscannotbe given reliably. Measurement unit

BS 4142 [22] identifies the A-weighted equivalent continuous noise level, LAeq, as the preferred measurement unit, althoughif the industrial noise is reasonably steady, an average A-weighted noise level measuredwith a sound level meter set to 'slow' time weighting is acceptable. It is necessary to obtain the background noise level when considering the impact of industrial noise and this is defined as the A-weightednoise level exceeded for 90% of a time period, LAOO T This should be measured by a noise analyser operating with a fast time weighting. Although detailed consideration is not given in BS 4142 to the likely impact of impulsive-type noise sources, except in applying a fixed correction, the maximum noise levels of a process should always be obtained for subsequent assessment. Legislation and criteria

For industrial development, Section 80 of the Environmental Protection Act 1990 [23], as amendedby the Noise and Statutory Nuisance Act 1993 [24], is relevant. Planning guidance is given in PPG 24 paragraph 19. The likelihood of complaints about noise from industrial development can be assessed using guidance in BS 4142 [22]. Basically, the noise level likely to be generatedbythe development, corrected where appropriatefor its character, is compared to the existing backgroundnoise levels. This process is described in more detail later. The resulting difference gives an indication of the likelihood

Environmental acoustics

27

ofcomplaints. If by this method, noise from the proposed Appropriate conditions will need to be imposed to meet then these requirements and examples are given in Annex4 of development 'is likely to give rise to complaints' the PPG 24 is to be In [3]. Appropriate conditions have subsequently determining permission unlikely granted. it will been noise level from a proposeddevelopment, published in Appendix A of the Departmentof the predicted be necessary to take account of the plant operating at its Environment's Circular 1/85 [26] and are reproduced maximum capability. Planning guidance on noise from surface mineral extraction or landfillsites is given in MPG 11: The Controlof Noise at Surface Mineral Workings [25]. These guidelines recommend a noise prediction model representing a proposedmineral development anda methodfor settling noise limits. They also provide adviceon noise monitoring and noise control. If plant associated with the mineral extraction or landfill is fixed on site it seems appropriate for this plant to be assessedon the basis ofBS 4142 [22]. If a local authority gives permission for the development, theywill need to ensure that:

than those proposedby the devel• noisierprocesses oper are not allowed, and of the submitted plans which • all physical features levels are in the finished control noise development.

incorporated

here in Table 1.9. Although conditions relating to the physical characteristics of the development, the type and intensity of activity to be carried out, and hours of operation, are preferable, in some instances a condition laying down a maximum noise level at a particular locationor possiblydifferentlevels for different periodsof the day may be appropriate. If a proposed development were shown by a noise assessmentto be acceptable during normal working hours but not at other times, it would be reasonable to apply a condition restricting operation to certain specified hours rather than rejectthe application altogether.

Using this guidance, permission will be given for developments against which the local authority is unlikely to find it necessary to serve a noise abatement notice under the Environmental Protection Act. However,it will not necessarilyprovide protectionagainst legal action by private citizens.

Table 1.9 Suggested models of acceptable conditions relatingto noisefor use in appropriate circumstances. Extractedfrom Appendix A ofDepartment ofEnvironment Circular 1/85 [261 [activities] shall

5

nottake place anywhere on the site exceptwithin

building[s].

The condition shoulddescribe precisely the activities to be controlled as well as the particularbuilding(s)

in which they areto take

place.

6. The building shall be so [constructed/adapted]as to provide sound attenuation against internally generated dB averaged over the frequency range 100 to 3150Hz. noise of not less than 7. Noise emittedfrom the site shall not exceed [A] dB expressed as a [B] minute/hour LAeq between [c] and [c] hours Monday to Friday and [A] dB expressed as a [B] minute/hour LAeq at any other time, as measuredon the [D] boundary [boundaries] of the site/atpoint[s] [E]. — Specify: A noise level

- period D boundary (boundaries) E - points. B

C

times

—

am on weekdays and am 8. [No {specfied machinery] shall be operatedon the premises] before on Saturdays nor after pm on Saturdays [nor at any time on Sundays or pm on weekdays and bank holidays]. 9. Before [any] [spec!fied] plant and machinery is used on the premises, it shall be enclosed with sound-insulating material in accordance with a scheme to be agreedwith the local planningauthority. This condition might be varied where the need was to secure the satisfactory mountingofthe machinery to prevent conductednoise and vibration. Adviceshouldbe appended to the permission, indicatingthe attenuation aimed at. 10. Development shall not begin until a scheme for protectingthe proposeddwellings from noise from the road has been submitted to and approved by the local planningauthority; and all works which form part of the scheme shall be completed before any of the permitted dwellingsis occupied. Authorities should giveapplicants guidance on the extent of noise attenuation to be aimed at within or around the dwellings, so as to provide preciseguidelinesfor the scheme to be submitted. and 11. Aircraft shall not take off or land exceptbetween the hours of NB. Additions and amendments

to these conditions are given in Annex4 ofPPG 24 [3].

28

Acoustics in the Built Environment

Diagram 1.9 Industrial noise assessmentprocedure

Under Section 80 of the Environmental Protection Act, computer model. This will require data relatingto sound the local authority is empowered to deal with noise power levels and directivity and is likely to necessitate a

nuisanceby serving a Noise Abatement Notice. three-dimensional model taking into account different BS 4142 Methodfor rating industrial noise affecting mixed heights above a ground level datum. residential and industrial areas [22] describes methods for The sound power level data may need to be estimated determiningnoise levels from factories, industrial prem- by converting,anticipated internallevels within a building ises, or fixed installations and sources of an industrial to those radiating from an aperture or from wall elements nature in commercial premises. The noise level deter- or obtained for external sources such as transportation mined in terms of LAeq,1 is corrected for tonal and from references. impulsive character to establish the rating level. This rating level is then compared with the measured batk- Noise control ground noise level. Even wherethe noise climate is always There are a numberofalternative methods ofcontrolling affected by the industrial noise, it is possible to measure noise from an industrial development including: the background noise level at another location whereit is attenuators in ductwork of ventilation or extraction presumed to be equivalent. The process is shown in systems 1.9. Diagram enclosures around mechanical plant like fans and The difference between the rating level and the motors, selection of low-noise components background noise level indicates the likelihood of comcladding on ductwork plaints. A difference of around 10 dB or more in LAeq T silencers in pipework serving valves or engine indicates that complaints are likely. Adifference ofaround exhausts 5dB is of marginal significance. At a difference below orientationduring design to avoid openings building 5dB, the lower the value the less the likelihood that like doors facing sensitive areas will occur. A difference of —10 dB is a positive complaints construction building indication that complaints are not at all likely. In assessing hours of operation to avoid night-time/evening whethera particularprocess is causinga noise nuisance, periods if possible the local authority would normally use BS 4142: 1990. methodsof operation to avoid high levels of impact Prediction

As stated earlier, industrial noise sources can be ofvarious forms and prediction of industrial installation noise requiresa clear understandingof the processes involved. Ideally, noise levels should be measured during the operation of similar processes elsewhere. It may be necessaryto takeaccountofan increase in size or capacity ofan operation.Onlyin the case ofmineralextraction are there suitable data to enable reasonably accurate predictions to take place and these are provided in BS 5228, particularly Part4. Data obtained in this way can make the prediction exercise easier since it will normally only require a distance correction to be applied. Where a large number of sources are identified it may be necessary to preparea

• • • • • • • • noise • lining bins collecting metallic waste material

Implementation of any noise control needs to take account of other parameters, for example cooling needs and fire ratings, so requirements need to be checked for overall practicality with the manufacturers and/or the suppliers. Leisure noise

Noise due to leisure activities can be considered as an extension to industrial noise. Leisure activities include discotheques, night clubs, cinemas, ten-pin bowling and clay pigeon shooting. In addition, certain apparently quiet activities such as ice skating can be a potential noise

EnvhnmeiitaI acoustIcs

problem due to the accompanying use of a sound

x

29

Vertical

system.

PPG24 [3] identifies that these activitiesposeparticular not least because associated activitiesare often at their peak in the evening and late at night. It is also necessary to consider traffic and associated car parking difficulty,

resulting from leisure activities. Units are as those described for industrial noise, but due to the nature of leisure activity noise, it can be the maximum levelwhich is the most important. Legislation is primarily as given for industrial noise. Additional guidance in assessing and setting criteria is given for certain leisure activities in the form of draft codes of practice, some ofwhich are being considered by the Departmentof Environment. Examples include: clay pigeon shooting [27] discotheques [28] water skiing [29] The Noise Council has prepared a code on pop concerts[301. Guidelines are intended to minimize annoyance at noise-sensitivepremises: The LAeq music level during any 15-minute period from events held on no more than 3 days/year should not exceed 75dB near urban stadiaorarenas, or 65dB near other urban or rural venues. Where between 3 and 12 events per year are held, the LAeq music level during any 15-minute period should not exceed the background noise level by more than 15 dB. For indoorvenues used for up to 30 events per year the LAeq music level should not exceed the background noise level by more than 5 dB. No music noise should be audible within noisesensitive premises between 23:00 and 09:00 hours. However, in some cases it may be necessary to set additional limits to control low-frequencynoise levels. Prediction of noise due to various leisure activities is best dealt with by using data from existing activities and making corrections to take account of site-specific factors. As well as those methods identified for industrial noise control, including building construction and orientation to avoid doors andwindowsfacing sensitiveneighbours, it may be possible to electronicallycontrolthe sound system output.

Vibration source Line or point

Z9

Radial (horizontal)

Longitudinal (horizontal)

• • •

Human responseconsideration Foot — head Right — left Back— chest

Figure 1.12 Threedirectionsofvibration measurement

•

•

Unit,

Groundbornevibration is typically measured in terms of

velocity (millimetres per second) or acceleration (metres per second per second). Where sources are impulsive or intermittentit is the peakparticle velocity or acceleration which is measured and this is the maximum value

recordedduring an event. General advice on the measurement of vibration in buildings is contained in BS 7385: Part 1 [31]. Vibration can either be considered in termsof the cause ofpossible building damage, where peak particle velocity is the preferred unit, or the effect on people where either velocity or acceleration can be considered. In determiningthe overall vibration value, it is necessary to take account of the vibration levels in the three perpendicular directions, up—down, side-to-side, and front—back, as illustrated

in Figure 1.12.

Legislation and criteria Guidance on acceptable vibration levels to avoidvibrationinduced damage in structures is given in BS 7385: Part 2

[31]. The guide values are given in Table 1.10. Prior to 1993, the guidance given in German StandardDIN 4150: Part 3 [32] was often used; DIN 4150: Part 3 values are Groundbonie vibratiou more stringentthan BS 7385: Part 2 values. As shown in Sources In addition to the airborne noise levels caused by Figure 1.13 from Reference 14, vibration can be felt at

transportation, construction and industrial sources discussed above, thereis also the generation of groundborne vibration to consider; this can lead to structureborne noise, perceived vibration or, in rare instances, building damage. Typical causes of vibration are trains, vibratory rollers, piling equipment and possibly industrial presses or blasting. Unless there are any irregularities in the road surface (for example, 'sleeping policemen' or expansion joints), road vehicles cause relatively low levels of vibration. The ground conditions are important since the vibration levels can be amplified significantlyif the soil is marshy/soft.

levelswell belowthose that could cause structural damage. BS 6472 [33] provides guidance on satisfactory magnitudes of building vibration with respect to human response. The factors used to specii' satisfactory magnitudes are given in Table 1.11. (Curves relating to these factors are shown in Figure 3.2.) Complaints from building occupiers about excessive vibration are normallydue to the beliefthat ifthe vibration canbe feltthen it is likelyto cause damage. Door closure or footfall within buildings often cause levels wellabove those measured from thesourceunder investigation. Considerationofstructurebornenoise is onlylikelyto be neededfor very sensitive areas such as auditoria, studios and con-

30

Acoustics

in the Built Envimnment

• the likely response of the structure of the building

under consideration. It is very difficult to obtain accurate data on the above andit is essential to undertakemeasurements on siteor in a location representative of site conditions. Reasonable data are availablefor such activities as blasting from the US Bureau ofMines withoutmeasurement but this should be added to by checkmeasurements if possible. Unless there is a similar building located at the same distance from the vibration source, it is not possible to measure the response of the building. A finite element analysismaybe necessaryto determinethe likelyresponse of the building.

-40

0

Control

If there is a

likelihood of structural damage then,

obviously, an alternative form of the source of vibration needs to be found or possibly the structure could be reinforced. However, only rarely is it shown that structural damage is likely to be caused and the method of control normally available is the isolation of the recipient, typically:

(H

• small sensitive equipment, for example balances • entire buildings, for example concert halls • individual rooms, for example studios.

Figure 1.13 Criteriafor subjectivelimits and building damage

ference meetingrooms. Spaceswith windows to outside are unlikely to be of concern since there will be a reasonably high level of low frequency noise breakinginto the space viathe windowswhich will mask any structurebornenoise. Establishing acceptable levels of structurebornenoise in sensitiveareas will need to be site specific.

optical

Onlyoccasionallyis it possible to isolate the source, since it is out of the control ofthe developer, although this has been undertakenwith railway tracks and some industrial sources such as presses. It may also be possible to control the operating time of the vibration source to avoid sensitive periods.

Iedidion In predicting the likely vibration levels from a particular New developments as a noise source source, consideration needs to be given to: In assessing the new development as a noise source, the type of source and its interaction with the consideration may need to be given to undertaking an Environmental Assessment or simply to meeting a planground, transmission through the ground, ning condition.

• •

Table 1.10 Transient vibration guide values for cosmetic damagefrom BS 7385: Part 2 [31]. Peak componentparticlevelocity in frequencyrange of predominant pulse Line

Type ofbuilding

4Hz to 15Hz

1

Reinforced or framedstructures Industrial and heavy commercial buildings Unreinforcedor light framed structures Residential or light commercial type buildings

50mm/sat 4Hz and above

2

15mm/s at 4Hz increasing

to 20mm/sat 15Hz

Note 1. Values referredto are at the base ofthe building. Note 2. For line 2, at frequencies below 4Hz, a maximum displacement of 0.6mm (zero to peak)

15Hz and above

20mm/sat 15Hz increasing to 50mm/s at 40Hz and above

should not be exceeded.

Environmental acoustics

31

Table 1.11 Multiplyingfactors used to specify satisfactory magnitudes of building vibration with respect to human response (fromBS 6472) [33]. Extractsfrom BS 6472 are reproducedwith the permission ofBSI. Complete copies ofthe standard can be obtained by postfrom BSI Publications, Linford Wood, Milton Keynes, MK14 6LE Multiplyingfactors Place

Critical working areas (e.g. some hospital operating theatres, some precision laboratories, etc.) Residential

Office

Time

Continuous vibration (see note 2) 1 1

Day

Night Day

1

1 (see note 3)

60 to 90 (see notes 4, 5, 6)

Night

1.4

Day

4 4

128 128 (see note 7)

8 8

128

Night Workshops

2 to 4

(see note 4)

Intermittent vibration and impulsivevibration excitation with several occurrencesper day

Day

Night

20

128 (see

notes 7 and 8)

Note 1. This table leads to magnitudes of vibration below which the probability of adverse commentis low (any acoustic noise

caused by structural vibration is not considered). Note 2. Doubling of the suggested vibration magnitudes may result in adverse comment and this may increase significantlyif the magnitudes are quadrupled(where available,dose/responsecurves may be consulted). Note 3. Magnitudes of impulse shock in hospital operating theatres and critical working places pertain to periods of time when operations are in progress or critical work is being performed.At other times magnitudes as high as those for residences are satisfactoryprovided there is due agreement and warning. Note 4. Within residential areas people exhibit wide variations of vibration tolerance. Specificvalues are dependentupon social and culturalfactors, psychologicalattitudes and expected degreeofintrusion. Note 5. The 'trade off' between number of events per day, their magnitudes and durationsis not well established. In the case of blasting, and for more than three events per day, the followingprovisionalrelationship can be used to modify the factors for residences in column 4 of this table. This involves further multiplying by the factor F= 1.7 N°5 where: Nis the numberof events in a 16-h day; Tis the duration of the impulse and decay signal for an eventin seconds. The duration of an eventcan be estimated from the 10% (—20dB) points of the motion time histories.

T'

d = zero for Tiessthan 1 s. Forshortdurationstimulithereis evidence that forwooden floors the human response d=0.32 and forconcrete floors d= 1.22. This 'trade off' equation does not apply when values lower than those given by the factors for continuous vibration result. Note 6. The root mean quad (r.m.q. = (l/Tf, a4(t) dt)"4) of the weighted acceleration signal a(t) may be used as an alternative methodof assessmentfor impulsiveevents. The same relation between duration and acceleration maybe used to accumulate the exposure to intermittentvibration occurring throughoutthe day (i.e. accumulated value = a4 (t)dt). The value obtainedby this method, which shouldbe related to the boundaries for continuous vibration, allows greater magnitudes with shorter and/or less frequent periods ofintermittentvibrations. Note 7. The magnitudes for impulsive shock excitation in offices and workshop areas should not be increased without considering the possibilityof significantdisruption ofworking activity. Note 8. Vibration acting on operators ofcertain processes such as drop forges or crushers, which vibrate working places, maybe in a separate category from theworkshop areas considered in this table. The vibration magnitudes specified in relevant standards would then apply to the operators of the exciting processes.

f

Environmental assessments

There is a formal requirement in the UK and the rest of Europe for an Assessment of Environmental Effects and the preparation of an Environmental Statement to be undertakenfor certain projects. The projects that require an assessmentin every case are listed in Schedule 1 ofthe

Town and Country Planning (AssessmentofEnvironmental Effects) Regulations 1988 [34] andinclude oil refiner-

ies, power stations, waste disposal and chemical installations, andlarge transportation schemes. Schedule 2 ofthe Regulations identifies projects which require an assess-

ment if they are 'likely to have significant effects on the environment byvirtue offactors such as their nature, size, and location' and include developments such as mineral extraction, industrial complexes, food industry, infrastructure projects, and holiday villages or hotel complexes. If the project under consideration is deemed by the local planning authorities to be included in either Schedule 1 or 2 then it is likely that an acoustics appraisal would need to be included as part of the assessment. In some cases, the local authority may considerthat only an acoustics appraisal is needed. The method ofapproachis

32

Acoustics

in the Built Euviroument

Establish baseline conditions during period representativeof development use Predict/estimate noise and/or vibration due to development use during both construction and operation phases Assessimpactof development by comparing existing and predicted levels Discuss situation with local representative Determine appropriate mitigation measuresif

] ] I

necessary

J

Presentoutcome of environmental assessment

1

Diagram1.10 Environmental Assessment: acoustics appraisalprocedure

shown in Diagram 1.10; Schedules 1 and 2 are summarized in Table 1.12. There is a proposal to amend the Regulations by extendingSchedule 1 by 14 new categories andclarifying those projects requiring environmental assessment in Schedule 2. It is likely that these amendments will come into force at the end of 1997. Included in Schedule 2 are wind farms and theme parks. The assessment guide for noise from wind farms was published in September1996 by ETSU [35]. The assessment for an Environmental Statement will need to consider the construction andoperationalphases of the development, including likely transport movements. It will also need to include those elements of acoustic appraisal identified earlier, particularly a site survey. Some site uses in sensitive areas will not be acceptable even with noise control measures, and planfling permission for a new development may be refused on environmentalgrounds.

Planningconditions Noise emission from the development, or, in the case of affected dwellings, sound insulation measures, will be issues covered by conditions imposed as part of the grantingof planningpermission. Table 1.12 Descriptionsofdevelopment Conditions imposed upon a planning agreementmay also refer to the construction andoperational phases and Schedule 1 will vary from district to district depending on local parameters. Local planning authorities may impose Those developments requiringassessment: 'standard' conditions as part of the issuing of planning Refineries permission. Table 1.9 identifies model conditions which Power stations were briefly discussed under 'Industrial Noise'. These Radioactivewaste stores should be checked carefullyand the questions that need Works for initial meltingof cast iron and steel to be asked are: are theyclear in intent or too 'catch all'? Asbestosextraction or processing installations Is the local authority being reasonable in allowing normal Integratedchemical installations activity and plant noise related to the site use for which or roads, tracks, Special long-distance railway airports permission is granted, or related to existing site noise levels, or is it impossible to operate normally without Trading ports Waste disposal installations falling foul of noise limits set arbitrarily too low? Has the Land-fill sites design team to demonstrate by a prediction statementthat the limits set will be met? Does a Condition apply only to Schedule2 'fixedplant' oralso to traffic movements and activity noise (for example, discotheque sound systems)? Do the same Many projects require assessment in the following standards apply to intermittentnoise sources like standby categories: generators? The setting of noise control standards at the planning Agricultural processes Extractiveindustries stage and their subsequent observance by the developer or owner does not preclude an individual taking legal Energy industries Metal processing action in common law to abate noise nuisance arising Glass making from the development. The developer who undertakes a Chemical industries 'shell' major development with subsequentfitting-out by Food industries tenants, should be careful in obtaining consents for the total development and agreeing contracts that tenants' Textile, leather, wood and paper industries Rubber industries plant complies with any planning condition and indeed has been allowed for as a contributing component of Infrastructure projects including industrial estate noise breakoutto the local community. development, urban development, and road, harbour, or airport construction not falling into Schedule 1 projects Construction phase assessment Other projects including holiday villages or hotel Reference earlier to dealing with construction activities complexes shouldprovide sufficient information to enablea suitable Modificationsto any projects previouslyin Schedule 1. assessment to be made. However, once the hours of working and the type ofmachinery to be used are agreed,

Environmental acoustics

i.e. the best practicable means have been employed, there couldbe a requirementfor a substantial degree of public relations activity to satisf' potentialcomplainants. Operationalphase If the development is industrial then adequate guidance may be obtained from earlier guidance dealing with industrial noise. This is also likelyto be the case for those developments with mechanical plant for building services as their only noise source — a topic covered in detail in Chapter 3. Suitable criteria have to be set at the most appropriate locations, normally the site boundary, and discussions with the Environmental Health Departments of the local authorities should lead to an agreement. In the case of steady noise from mechanical plant, a noise level criterion matching the existing background noise level is normally appropriate. Consideration may need to be given to a criterion 5dBA below the background noise level in some cases to avoid any significant increase in a particularly sensitive area, but 10dBAbelow the backgroundshould never be necessary. Noise from other activitiessuchas leisure, for example night clubs or ten-pin bowling, will need to be carefully considered since music or impulsive noise can be annoyingeven at noise levels below the existing background. In some cases the only means of control may be a restriction on hours of use. If there are noise problems once a development is operational, the first line of complaint is frequently the local authority Environmental Health Officer. He may have been asked to commentby the planningauthority at planningstage on whethera noise condition should apply, and reacts to the later complaints by carryingouthis own checks. If he agrees that the complaint is reasonable and may constitute a Nuisance, he can issue an 'Abatement Notice in respectofNoise Nuisance' under the provisions of the Environmental ProtectionAct 1990which gives 28 days to remedy, restrict, or stop the noise. The action to improve matters mayvary from 'best practical means', i.e. achieving as much as costs and practicalities allow to provide some amelioration, to radical noise control measures or proscribing activity or plant noise during certain times or even altogether. Once a Notice is served, an Appeal can be made against the basis of the alleged occurrences constituting the statutorynuisance. However, the Notice provisions are not suspended until the appeal court so decides. Alternatively, a Court Order to restrain a continuation of a wrongful act or omission may be initiated. This is the most common legal action in private nuisance claims. Failure to comply could mean fines and even imprisonment. Unlike a Notice, the restraint requirement is immediate. Further details can be found in Garner's Environmental Law [36].

33

3. Department of the Environment Planning Policy Guidance PPG 24 Planning and Noise, HMSO, 1994. 4. Wimpey Laboratories Ltd Residues and Emissions: Sound and Vibration, Report No. 15, CTG Channel Tunnel Project — Environmental Impact Assessment, Hayes, Middlesex, September 1985 5. BS 6698: 1986 (amd 1991) Specffication for integratingaveraging sound level meters, British Standards Institution, Milton Keynes 6. BS 5969: 1981 Specficationfor soundlevel meters, British Standards Institution, Milton Keynes 7. Organisation for Economic Co-operation and Development, Fighting Noise in the 1990s, OECD Publications Service, Paris, 1991 8. The Department of Transport Calculation of Road TrafficNoise, HMSO, London, 1988 9. Statutory Instrument 1975 No 1763 Building and Buildings NoiseInsulationRegulations, HMSO, London, 1975

10.

Land Compensation Act 1973, HMSO, London,

1973 11. BS 8233: 1987 Codeofpractice for sound insulation and noise reduction for buildings, British Standards Institution, Milton Keynes 12. The Noise Advisory Council A Guide to Measurement and Prediction ofthe Equivalent Continuous Sound Level Le:j, HMSO, London, 1978 13. Shield, B. M. and Zhukov, A. N. A survey ofannoyance caused by noisefrom the DocklandsLightRailway. Institute ofAcousticsProceedings, 13(5), pp. 15—23 (1991) 14. Nelson, P. (ed.) Transportation Noise Reference Book, Butterworth-Heinemann, Oxford, 1987 15. Statutory Instrument1996No 428. The NoiseInsulation (Railway and Other Guided Transport Systems) Regulations. 16. DepartmentofTransportRailway Noise and the Insulation of Dwellings, Mitchell Report, London, HMSO, 1991. 17. US Environmental Protection Agency Office ofNoise Abatement and ControlInformation on Levels ofEnvironmental Noise Required to Protect Public Health and Welfare with an Adequate Margin of Safety US Government Printing Office, March 1974 18. Departmentof Transport Calculation ofRailway Noise 1995, London, HMSO, 1995. 19. Control of Pollution Act 1974 20. BS 5228: 1992/1997 Noise control on construction and cpen sites, British Standards Institution, Milton Keynes 21. Department of the Environment Control of Pollution Act 1974, Implementation ofPart 3: Noise, Circular 2/76, HMSO, London, 1976 22. BS 4142: 1990 Method ofrating industrial noise, affecting mixed residential and industrial areas, British Standards Institution, Milton Keynes [BS under review] 23. Environmental Protection Act 1990 24. Noise and Statutory Nuisance Act 1993. References 25. Department of the Environment Mineral Planning 1. This CommonInheritance, Government White Paperon Guide MPG 11 The Control of Noise at Surface Mineral the Environment, 1990 Workings, HMSO, 1993. 2. Department of the Environment Report of the Noise 26. Departmentof the Environment The Use ofConditions Review Working Party 1990, Batho Report, HMSO, in Planning Permissions, Circular 1/85, HMSO, London, 1985 London, 1990

34

Acoustics in the Buift Environment

of practice on Noise from Clay Pigeon Shooting, Midland Joint Advisory Council for Environmental Protection, 1989, revised 1991 Noise AdvisoryCouncil Draft Code ofPractice on Sound Levels in Discotheques, HMSO, 1986 British Water Ski Federation Code ofPracticefor Water Skiing and Noise, 1989/Consultation draft for revised Code October 1996. The Noise Council Code of Practice on Environmental Noise Control at Concerts, The Noise Council, 1995. BS 7385: Part 1: 1990 Evaluation and measurementfor

27. Code

28. 29. 30. 31.

vibration in buildings: guidefor measurementofvibrations and evaluations of their effrcts on buildings, British Standards Institution, Milton Keynes. Part 2: 1993 Guide to damage levelsfrom groundborne vibration.

32. Deutsches Institutfür Normunge.V. 4150: 1986: Part 3 Structural vibration in buildings: effects on structures,

Berlin 33. BS 6472: 1992 Guide to evaluation ofhuman exposureto vibration in buildings (1Hz to 80Hz), British Standards Institution, Milton Keynes 34. Town and Country Planning (Assessmentof Environmental Effects) Regulations 1988, SI 1988 No. 1199,

HMSO, London, 1988

35. ETSU The Assessment & Rating ofNoisefrom Windfarms,

The Working Group on Noise from Wind Turbines,

36.

ETSU-R-97, Final Report September 1996. Garner,J. E, Harris, D.J. (eds) Garner'sEnvironmental Law, Butterworth-Heinemann, Oxford,first published

July 1942, updated three times p.a.

Sound waves in the air on the source side impinge on the partition and 'drive' it (i.e. cause it to vibrate), and in turn the barrier radiates sound into the receiving space. The main issues are the transmission path, the soundreducing capability of the separating structure, and the components making up this structure. The practical reduction ofairbornesound energy is not only dependent on the direct path via the wall, but also on flanking

Chapter 2 Design acoustics Duncan Templeton

paths. Sound insulation

Airbornesoundinsulation Airborne sound insulation entails the separation by a physicalbarrierofthe space containing a noise source from an adjacent space requiring protection. The physical barriermaybeapartitionorwallbetween rooms orfloor for rooms above each other (Diagram 2.1). The term 'partition' implies dry construction (modular panels or clad studded frames) or lightweight,non-loadbearing masonry; 'wall' implies a masonry structuretied into other wallsand supportingfloors or roofabove.There is, however, overlap between the terms. The two systems have differing characteristicsacoustically. Partitions may be more subject to edgecracking,flankingandresonance effects. Walls can transmit structurebornesound more than studding-type partitions, or pass re-radiated energy,andwithoutspecial detailingare moredifficult to make discontinuous.

Flankingpaths Flanking paths occur at the edges of the physical barrier, its junction to floors, other walls, ceiling, or ductwork common to source andreceiving rooms (Figure 2.1). The indirecttransmission via a flanking path can be reduced by increasing the massofthe flanking walls, increasing the partition mass and bonding it to flanking elements, or introducing discontinuity to side walls in the adjacent rooms, for example by independentwallliningor floating floors. Sound level difference The soundlevel difference between two spacesis dependent on the sound-reducing capability of unit area of the partition,the area of the partition, the acoustic properties of the source and receiving spaces, and flanking effects (Figure 2.2 and Diagram 2.2).

• Area of TRANSMISSION PATH

partition

•• Stiffness • Coincidence Partition • resonances Composite

SRI

construction

•WaIIs

• Roofs • Floors COMPONENTS

•• Doors • Ceilings Partitions Diagram 2.1 Sound insulation: considerationsin design

36

Acoustics in the Built Environment

0 0 LU C-,

0 U) A = Sourceroom B

= Receiving room z0 II-

4 Via other rooms 2 Via flankingwalls 3 Via ceiling 4 Via floor 5 Direct path through wall 1

Figure2.1

0 0

z>

Commonnoiseflanking paths

LU

U LU

Diagram 2.2 Separation between rooms

A, Absorption units

Partition Area, s = h x I m2

S

0= R—1O log —

A where 0is sound level difference A is sound reduction index for unit area of partition.

Figure 2.2 Soundlevel difference between rooms

37

Facade Area (SI

separate calculation

for sound via other facadesand openings Inside-to-outsidesound level difference

OL1—L2

= R— lOlog S+ 14 + 20 log r Figure 2.3 Inside-to-outside sound level dfference Facade Area (SI

A, Absorption units separate calculation for sound via other facades and openings

SRI (A)

Outside-to-insidesound level difference

o = L1 — L2 = R — 10

log —6 dO

Figure 2.4 Outside-to-inside sound level dfference sound level dfference. This is defined in Chapter 5. It is often useful in a sequence of measurementsfor spacesat differentstagesoffit-out to have a level difference standardized to a reference half second reverberation time. The Weighted Standardized Level Difference (DflT,W) is defined in BS5821 [1] and referred to in the Building Regulations Part E [2]. Iftwo spacesare similar in acousticalcharacter, i.e. have the same amount of absorption in both the source room andreceiving room, the measured level difference will be the same whichever is the source room, If one space is much 'deader' than the other,or the spaces are ofsimilar reverberation timebutgreatly different involume, the level difference will be greater with the deader (or larger volume) space as the receiving room. This is not an anomalyalthougha partitionapparently more effectivefor sound insulation in one directionthan in the other can requiresome explanation to a client. In fairlydead spaces, forexample cinemaauditoria orstudios,a truereverberant field in the receiving room may not be generatedby the source in the room adjacentand there will be agradientof soundlevel awayfrom the separating partition. Room-to-room

Inside-to-outsidesound level difference. This is given by:

D=R— 10 log S+ 14 + 20 log r for facade radiation to hemisphere, where Sis the outside wall area and ris the radius from the facade centre to the

receiving point, or in other situations as defined in Chapter5 (Figure 2.3).In practice, an assessmentofnoise break-out from say a factory building requiresa sequence of calculations involving the contributions of sound via the roof, other facades, doors and windows. Little useful informationexists aboutsoundradiation viaangled roofs. In mostcases,itis the openings in industrial buildings that determine the noise break-out to adjacentsites. Outside-to-insidesound level dfference. This is given by: D R— 10 log S/A —6dB

This assumes that the measuring microphone is well away from the facade. As with break-out, break-in calculations shouldanalyse components ofnoise from the other faces and roof (Figure 2.4). While separate checks follow for break-in and break-out, both may be of concern on some jobs; for example, a hospital may be considered a noisesensitive building type but has significant 24-hour noise from plant and activity, which may upset nearby housing (Diagrams 2.3 and 2.4). Sound reduction index The sound reduction index (SRI) is the basic measureof sound insulation andis the number ofdecibels that sound power is reducedby transmission through the barrier. The average sound reduction index is usually expressed over 100—3150Hz one-third octavebands, andwill be similar to the single value at 500 Hz (see Chapter 5).

38

Acoustics in the Built Environment

Diagram 2.3 Comparing buildinguse and external noise climate NOISE BREAK-IN

• Compare to

criterion

NOISE BREAK-OUT

• Neighbourhood properties or site boundary

Diagram 2.4 Noise break-in and break-out theoretically increases by 6dB per octave. It may be seen from Figure 2.5 that the empirical mass law curve based on results is below the theoretical curve due to coincidence and resonance effects, and approximates to 5 dB per mass doubling. The theoretical soundinsulation over the frequency range 100—3150 Hz is given by: R = 7.6 + 20 log MdB acuity at lower frequencies. where M is in kg/rn2; alternatively, to determine the theoretical performance at a particularfrequency: Mass law The mass law indicates that in theory sound insulation R= 20 log (JM) — 47dB increases by 6dB for every doublingofweight ofdividing element per unit thickness. The sound insulation also where is the frequency of the incidentsound. Averagesound insulation index rating,

R

The average sound insulation index rating, R, is the weighted single-figuredescriptordefined in Chapter5. As with the A-weighting, greatersignificance to midandhigh frequencies is given than for, say, the direct arithmetic average of the SRIs. This more accurately reflects the subjective effect of insulation due to the ear's reduced

f

Design acoustics

39

Table 2.1 Sound reduction indices OBCF (Hz) kg/m2 Single glazing (mm)

4-mm glass in aluminium frame, 100-mm opening

4mm 6mm 6.4mmlaminated

10 15

12mm 19mm

30 49

125

250

500

1000

2000

4000

Mean'

10 20 18 22 26 25

10 22 25 24 30

11

28 31

12

12

34 30 33 39 45

13 29 38 38 47 47

11

34

31

21

20 17

25 38 46 44 48 50 53

25 30 30 35 34 39 38

52 47 46 28 27

51

44 46 39 27 22

54 58

56 60 76 60 57 57 52 58

45 47 52 51 41 43 45

61

60 70

49 49 55

30

36 36

35

34

30

32

22

29 37 38 41 40 42

28 29 30 35 35

Doubleglazing: glass/air space/glass (mm)

Sealed units

3/12/3 4/12/4 6/12/6

22 20 25 26 26 27

4/12/12 6/12/10 6/20/12 6.4 lam/12/10 Separate panes 6/150/4 6/200/6 4/200/4

4/200/4,opposite sliders open 25 mm 4/200/4,opposite sliders open 100mm

Masonry/blockwoi* 102-mm single-leaffairfaced

Single-leafplastered both sides

Cavitybrickwork with ties Double leaf brickwork plastered both sides 100-mm lightweight blockwork fairfaced 100-mm blockwork plastered both sides 100-mm blockwork with plasterboard on dabs both sides 200-mm fairfaced lightweight blockwork 200-mm blockwork plastered both sides 200-mm blockwork plasterboard on dabs both sides Three-leaf brickwork plasteredboth sides Two leaves of 100-mm dense concrete blocks, 50-mm cavity, 13-mm plaster both sides, cavity ties

240 480 480 125

250 720

19

22 26 34 29

24 29 33 34 40 37

41

56 54

35 41

36 44 39 40 42

29 37 27 15 10

35 41 33 23 16

45

36 34 34

37 37

40

46

41

51

34

41

45 32

56 56

44

38 39 39 43

40 48 33 37 45 43 46 50 49

57

54 57 56 66

35

41

49

58

67

75

52

15

31

35

37

45

46

35

25

32

34

47

39

50

38

25 10

37 14

42 22

49 28

46 42

59 42

43 26

32

41

47

49

53

58

47

19

25

19

22 34

24

30 42 30 33 39

22 36 44 35 39 46

25 36 30 26 38

32 32 28 35 37 33

34 34

48 39 34 27

42 32 25

41 45

53 49 53 55

73

58 49 52 55

47 44 32 27

46

Stud partitions

9-mm plasterboard on 50 X 100mm studs at 400mm centres 13-mm plasterboard on 50 X 100mm studs at 400mm centres 13-mm plasterboard on 50 X 100mm studsat 400mm centres, 25mm mineralwool between studs 6-mm ply on 50 X 50mm studs at 600mmcentres Double 13-mm plasterboard on 146-mm steel studs at 600 mm centres Sheetmaterials/boards

9-mm ply on frame 25-mm T&G timber boards 5-mm ply/1.5-mm lead/S-mm ply composite sheets Two layers of 13-mm plasterboard 1.2-mm steel sheet, 18 g 6-mm steel plate

5

7

14

21

13 17

25 22

26 24 13 27

30 29 20 35

10

50

31

24 41

38 32 29 39

18

40

Acoustics in the Buift Environment

Table 2.1 Sound reduction indices — continued OB CF (Hz)

kg/rn2

Profiled metal sheeting 0.8-mm steel trapezoidal section, 50-mm deep cladding panels Duct cladding: plaster/mineralwool Duct cladding: lead foil/mineralwool 50-mm woodwool slabs, screeded to source side 100-mm woodwool slabs, screeded to source side

30 12 28

50

125

250

500

1000

2000

4000

Mean°

18

20

21

21

25

25

22

14

17 13

18 12 7 30 32

20

31 21

22

32 34

29 12 7 33 33

36 38

30

26

11

7 26 28

8 28 28

12 7

7

12" 7b

31

Docirs

43-mm flush, hollow-coredoor, normal hanging 43-mm solid core door, normal hanging 50-mm steel door with good seals Acoustic metal doorset, double seals Roors 235-mm T&G floorboards, floorjoists, 13-mm plasterboard and skin 235-mm T&G floorboards, floorjoists with 50-mm sand between, 13-mm plasterboard and skin 100-mm reinforced concrete slab 200-mm reinforced concrete slab 300-mm reinforced concrete slab 200-mm o/a: 125-mm concrete slab and screed on 13-mm nominal glass fibre

9 28

16

18 31

36 54

24 34 39 57

36

27 39

31

18

25

37

39

45

45

35

35 37 42 40

40

250 460 690

45

45 45 50 52

50 52 57 59

60 59 60 63

64 62 65 67

49 49 53 54

420

38

43

48

54

61

63

51

17 21

13 21

29 34 49

14 26 32 44

12

36 41

16 32

47

'Average 125—4000Hz octaves. SRI (100—3150Hz) 0—2dB lower. b+ value on duct performance.

An example of the effect of increasing weight may be seen bythe performance ofa brickwall.A single-leafbrick wall may be rated 45 dB average, a 225-mmwall 50dB, but it takes a thickness of 450mmto achieve 55dB, and this performance may well be compromised by edge flanking effects. The performances of typical constructions are scheduled in Table 2.1. A schedule ofdensities (kg/m3) of common building materials may be found in BS 648 [3].

tion is typically at lower to mid frequencies, 200—800Hz. However, there may be a high frequency benefit in practice also, because the quilt has an attenuatingeffect on sound via weaknesses at partition leafjunctions.The schematic sound insulation related to frequency is increased from single-panel6dB per octave slope to 12 dB by double leaves plus absorption, so the overall effect is greater improvement at higher frequencies. The sound reduction index will never rise to the arithmetic sum ofthe Sills ofthe individual leavesbecause Double leaves the two leaves canneverbecome totally isolated. However, Double leaves with a gap between allow greater sound it is usual to obtain a higher SRI from a double-skin insulation than a single layer ofequivalent weight. There construction than from the equivalent-weightsingle skin. are two main means of transmission: The principle applies for horizontal or vertical dividing i.e. roofs and floors as well as partitions. For a radiation from the first panel into the air space elements, of two leaves of like mass (inkg/m2) with partition excites the second panel, which radiates energy into of separation leaves d (in metres), the receiving room; structureborne transmission between the two leaves 85 by mechanical links, the second leaf radiating the

• •

transmitted vibrational energy.

Sound-absorbing quilt in the gap improves the sound insulation. A relatively small provision of absorption is effectivebecause it suffices to ensurethat the transmission via radiation is less than the structurebornetransmission. Although it contributes little to the total surface mass, it soaks up sound crossing the gap and standing waves of soundwithin the cavity. The improvement due to absorp-

I

rnd

f

The resonantfrequency can be arranged to fall below the frequency range of interest, say below 50Hz, by choosing a high value of din relation to rn. Some estimate of the average field sound reduction index can be obtained from the expression:

R = 34 + 20 log rnd

41 70

0

60

(/) a) a) C) co a)

x0) 40

0

>

U -D 0)

30

20

0

10

ii;ft/ ,ii 100

1000

U)

Surfacemass (kg/rn2)

Figure 2.5 Mass law: averagefield SRI 60

/

55 -D 50 U) a) C)

(2)

125 200 315 500 800 1250 2000 3150 5000 100 160 250 400 630 1000 1600 2500 4000

()

rd octave bandcentrefrequency(Hz)

/

45

57

Ct

.-.

40

10

3

35

-.-1 4

125

30 10

100

5

1000

Surface mass (kg/rn2) variation

3

of average SRI of double-leaf

partitionwith total surface mass 1 200 mm cavity 2 100 mm cavity 3 50 mm cavity 4 25 mm cavity

125

construction:effect on SRI Figure 2.6 Double-leaf

The effect is shown graphically in Figure 2.6. The minimum useful gap is 50mm and wide cavities improve

0.7 mm steelskin 2 60 mm mineral wool (90 kg/rn3) 3 2 x 13 mm plasterboard 4 Metalstuds at 600 mm Cs 5 25 mm glassfibre 6 Single-leaf common brickwork, plasteredboth sides (1920 kg/rn3) 1

the low frequency performance. Different characteristics (weight, thickness) to one leaf offers a further improvement, as the many tests on double glazing combinations demonstrate. Cavity walls in brickwork with ties offer Figure 2.7 Dry liningversus masonry negligible benefit to solid 225-mm construction. A good example of the performancepossible is the use of widecavityseparating wallsin multiplex cinemas where double 15-mm plasterboard either side of a 250-mm gap with fraction of the weight, to achieve 50dB average SRI, but 100-mm quilt inside consistently achieves 65—70 dB more care is required at the edge and at penetrations. In DflTW. dry construction, if substantial acoustic doors are used, a structural steel 'H' subframe bolted to the floor and the underside of the floor above shouldbe used to hold the Dry construction versus masonry

Dry construction versus masonry is a frequent design doorset firm; standard partition metal studs allow too comparison (Figure 2.7). A plastered block wall can be much flexing. This has to be borne in mind in any cost replacedby double-layer plasterboard with quilt inlay at a comparisons between systems. The acoustic integrity of

42

Acoustics

in the Built Environment

dry partitioningis more easily compromised by services penetrations, sockets and fixtures.

Discontinuity implies the separation of structural elements so thatvibrations are not easily transmitted around the mainstructure to cause intrusive noise in other areas Stffness by re-radiation. The ingredients for 'box-in-box' rooms The stiffness of thin panels is important because of the employing a consistent standard of discontinuity are susceptibilityof leaves to be more easily driven by a noise double or even treble walls, a floating floor, and a source on one side at certain frequencies. The effectcan substantial ceiling and slab above. be seen in duct systemswhere thin duct walls may easily transmit low frequencies of in-duct sound. Composite construction Composite construction is that consisting of surface areas Coincidenceeffect ofdifferentsound reduction indices, for example a brick The coincidence effecthappenswhen soundwaves falling wall containing a door and a window. The total sound on a panelexcite bendingwaves in it, the velocityofwhich power through a composite structure is the sum of the depends on frequency. Sound transmission is greater at components of sound power transmitted by each compothe frequencies where the coincidence effect is greatest nent separately (see Chapter 5). and the theoretical R is reduced by as much as 10 dB below the level derived from mass law calculation (see Sound leaks Sound leaks can have a serious deleterious effect on the Chapter 5 for full description). performanceofa partition, wall, floor or roof. The effect Partitionresonances is more marked at high frequencies. Figure 2.8 shows that Partition resonances happen when standing waves are a hole of 0.001 m2 makes the composite SRI 40dB for a formedwithin the partition.At the frequencies at which 45-dB-rated SRI wall of 16m2. Gaps at door edges are a this occurs the resonances will reduce performance.In a typical example of sound leakage. single-leaf partition or wall, the fundamental resonant frequency is determined by its stiffness. At higher fre- Buildingenvelope:rooft quencies, there are other performance 'dips' at har- Roofs are typically oflighter construction than outer walls monics ofthe resonantfrequency. For many partitions the and of relatively large area compared with walls and resonances occur at low frequencies outside the range of openings. The exposure to road, rail or industrial sources usual interest and the effect can often be ignored. is less, but a building can be vulnerable to aircraftnoise or However, it may be of interest when, for example, checking a specific curtain wall glazing arrangementfor low frequency components of traffic noise. The most 1:1 000000 importantis the fundamental resonantfrequency, calculated from: 1:500000

tr\;

f=-where

1:250 000

11 1 I—+—

[a2b2

0

a and b are the partition dimensions (m), t is its

thickness (m), E its Young's Modulus (Pa), and p density (kg/rn3) (Table 2.2).

Discontinuity

The discontinuity of rooms within a building can get complicated at junctions and is most practically implementedon smaller studiospaces than on majorauditoria.

CD

a)

-c 0) C

0 CD

(a

C

0 Cd, CD

a)

Material

Young's modulus, E

(Pa)

Density, p (kg/rn3)

CD

0 0 CD

cc

Lead Steel Aluminium Glass

Concrete Brick

Plasterboard Plywood

1.6 2 7 4 2.4 1.6 1.9 4.3

X 1010 X 1011 X 1010 X X 1010 X 1010 X iO X io

l0

11 300

8000 2 700 2 500 2 300 1 900 750 580

1:32 000

1:16000

a)

Table 2.2 Values of Young'smodulus and density

1:125000 1:64000

1:8 000

1:4000

1H1N-n-I

1:2 000 1:1 000 1:500 1:250 1:125 1:64

II

I

IIILltIIi

'II1 0

1:32

I

Cc? _______.'.1'-H-I-rtuInhIlC 1:16 ________

1:8

ftHNII1'WIIi'JtI 1:4 _________ ##f H 1:2

I II 'IJ

1:1 2:1

4:1 8:1

0

I

10 15 20 25 30 35 40 45 50 55 60 Loss of insulation : deduct from higher insulation (dB) 5

Figure 2.8 Compositeconstruction sound insulation

Design acoustics

roof-mounted items ofplant. Traditional slated roofs have a reasonable surface mass, butgaps up the lapping slates and the need to ventilate under the lapping slates make such roofs poor insulators (27 dB average) on their own. The usual use of a roofvoid with its thermal insulation and plastered ceiling increases this to 38 dB average. Flat roofs Flat roofs of built-up felt on thermal insulation on metal decking or composite construction of profiled metal, insulation and liner tray metal sheeting, achieve only 30—35 dB. Roofs of similar surface mass to floors — screeded topping to precast concrete, for example, with asphalt and insulation above — manage 45—50 dB. For performance exceeding 50 dB, the roof will have to be supplemented by a barrier ceiling below. A conventional lay-in grid mineral tile ceiling will be of little additional value to the roof,particularly if open grilles in the ceiling allow its use as a supply or extract air plenum. Lightweightroofs

Lightweight roofs with a profiled metal outer face are subject to rain and hail drumming, and can also 'click' and bang during thermalmovement. Damping the outer skin by having quilt directly behindit muffles the sound to a degree. Composite metal roofswith a soffit ofperforated metal are often used in sports halls — gymnasia,ice rinks and swimming pools — to absorb soundwithin the space, butthe position of the vapour barrier above the perforations needs considering carefully.Too thick a membrane will blank offthe absorption capabilityof the quilt above; some systems have the membrane embedded in the thermal/absorptionquilt, but special fixings through this arrangementare needed. Cethng To uprate the sound reduction capability of a roof, the suspension of a barrier ceiling can be included. The performance of a timber floor can be altered from 42dB to 58 dB by the addition of a British Gypsum M/F ceiling as shown in Figure 2.9. The system uses straightforward metal straps; some other specialist systems use resilient hangers, and any design will have to address problems of suspending ductwork or further decorative ceilings below the barrier ceiling. Ceiling voids

Ceiling voids are familiar transmission routes for sound between rooms, where partitions are not carriedthrough to the roof or floor above. Carrying the partitions up not only breaks the ceiling but inhibits moving them and affects ventilation arrangements — ducted supplies need the cross-talk attenuationdiscussed in Chapter 3. Ceiling manufacturers should be able to quote room-to-room transmission characteristics as measured in BS 2750: Part 9: Laboratory testing [411. Suspended ceilings

Suspended ceilings tend to be selected for their light weight (hence economy) andfor absorption, rather than sound insulation: the level difference through a ceiling is limited to 10—15dB. For greater performance a closed plasterboard ceiling can be used but recessed lights must

43

be cased and absorption is reduced compared to the proprietarytiled grid. Walls Blockwork

Blockwork performs reliably if well constructed and of adequate mass. Lightweight thermal blockwork (350—700kg/m3) frequently usedin the absence ofadvice otherwise, is poor. Unplastered blockwork loses sound insulation by its fissures and movement cracks: plastering can improve this. The best blockwork is 2000kg/m3 solid no-voids dense concrete masonry (dcm), a thickness of 190 mm achieving 50dB SRI. Target densityvalueswill have to be set outas there is no set definition of 'dense' except in terms of blockwork strength.Some strong blockwork (7 N/rn3) is not necessarily very dense at 1400kg/rn3. Brickwork

Brickwork is usually better than blockwork; the smaller units can be built around partitions more easily and movement cracking is less. The heaviest (2300kg/rn3) construction is obtained by using solid engineering bricks; an acceptable everyday use is commons laid with frogs up (1700—2000kg/rn3). Mortar density is typically 1800kg/rn3. Partitions

With care, lightweight construction can outperform masonry, certainly mass-for-mass, andsometimes even for similar thicknesses. In plasterboarded partitions, metal studding has largely replaced timber studding and gives better SRI performance because the leaves are coupled across the studs more resiliently. Plasterboard itselfis used less often as the range of metal-skinned modular panel partitioning diversifies and becomes more competitive. The panels take the form of50-or 100-mm-thick elements with absorption material in a core, for offices.For studios, noise havens or music practice rooms, panels can be perforated on the inner face for absorption and fixed to isolated floor and ceiling panels. A strong combination is masonry plus independent lining, with quilt in the cavity Some examples are shown in Figure 2.10. Care must be taken not to make the cavity too small, otherwise low frequency resonances can render the dry lining disadvantageous rather than advantageous to insulation.

be avoided if possible. Theyare frequently installed and then complained of in places where low background noise levels and need for Folding partitions. These should

confidentiality exist, e.g. solicitors' offices and boardrooms. Because of gaps around the suspension gear, the level difference either side is similar to a door's: 15—20 dB average. Folding panel rather than concertina types are marginally better, but beware of the claims of suppliers who quote high sound insulation values, even supported by tests, that relate only to the body ofthe panels and not to the total assembly. The best types have some closure seal — pneumatic or mechanical — which can lock the panels in place. A robust ceiling at head and a division of ceiling void are necessary. By care,separation in the order of around 35dB can be obtained: this can be related to

44

Acoustics

in the Built Environment 100

9C —

—

— —

8C —

V

1

0 U)

—

—

—

—

—

/ — N —— —

—

—

\

71

———————————————

\

.

-.-..

0.

N

E

a)

N 3

E

z0

1

20 125 200 315 500 800 1250 2000 3150 100 160 250 400 630 1000 1600 2500

rd octave band centre frequency (Hz) 1 Timber floor 2 Timber floor and suspended ceiling

(b)

3

Impact sound 4

6

0

2

III

200mm

18 mm chipboard 195 x 45 mm timberjoists 600 cs 3 13 mm gyproc 4 150 mm mm. spacing/ceiling void 5 80 mm gypglas 1000 6 13 mm gyproc on M/F suspension system 1

2

(a)

V x

50

C C

0

C)

V a,

Figure 2.9 Sound insulatingsuspended ceiling. (Courtesy of British Gypsum)

V

C

0

U)

125 200 315 500 800 1250 2000 3150 5000 100 160 250 400 630 1000 1600 2500 4000

rd octave band centre frequency (Hz) 1

(c)

Timber floor

2 Timber floor and suspendedceiling Airborne sound insulation

45

Design acoustics

Table 2.3

Table 2.4 Conversationprivacy taking account of

Speech privacy

Whether conversation overheardother side of

division

SRi" ofdividing

Normalspeech easilyoverhead Loud speech clearly heard Loud speech distinguished during normal activity Loud speech heard but not intelligible Loud speech can be heard faintly but

Sound as heard by occupant

SRI + background noise

20 25 30 35

not understood

40

Loud speech or shoutingheard with great difficulty "Average sound reduction

element (dB)

background noise

dBA

Intelligible Occasionallyintelligible Audible but not intelligible Inaudible

NR

70

65

75—80 80—90

65—70 75—85

90

85

45

index, 100—3150 Hz.

speech privacyneeds as shownin Table2.3. An alternative method is to add the background noise level and the partitionSRI and workto a total exceeding 65 (Table 2.4). Sound insulation performance is particularly important for speech privacy in the frequency range 500—2000Hz. Doors

'±

2

2

—X- 3

'4

÷4

I

\ \I N

-

The typical domestic door, hollow-coredwith a loose fit, achieves 15—20dB average. A solid-core door with fire ratingrebatesto the frameimproves this marginally. The fittingofintegralblade or compression seals to edgesand the threshold help the value up to about 30dB. Purposemade timber or metal doorsets can be selected in the range 35—45 dB average. The weight of acoustic doorsets is substantial and they must either be well fixed directly

xa, C C

0 C,

a' C

0

U)

___

111111111

200 ri,rr

single-leaf common brickwork 48 mm glass fibre (24 kg/rn3) 13 mm plasterboard (wallboard) on 48 mm. 'I' section metalstuds at 600 mm cs 4 2 x 19 mm Gyproc' plank, adhesive between layers 5 2 x 13 mm plasterboard

125 200 315 500 800 1250 2000 3150 160 250 400 630 1000 1600 2500 4000

100

rd octave band centre frequency (Hz)

1

2 3

-•-1 Rw=44dB —*3 Rw=55dB

Rw=58dB Rw=59dB

masonry/dry-lining combinations

Figure 2.10 Masonry dry lining combinations. (Courtesy ofBritish Gypsum) —

±2 +4

Design acoustics

47

Floor boards fixedthroughGyproc to flange 19 mm, Gyproc 3 Overlapping ledger channels on foam strip 4 Floor joists 5 100 mm Gypglas 1000 6 13 + 19mm Gyproc 7 Resilient bar 8 Sealant 9 Perimeter seal strip 1

2

8

III 0

11111

200 mm

V x

Va) C C

0 U

V VC

I

0

U)

125 200 315 500 800 1250 2000 3150 100 160 250 400 630 1000 1600 2500

125 200 315 500 800 1250 2000 3150 5000 100 160 250 400 630 1000 1600 2500 4000

rd octave band centre frequency (I-lz)

rd octave band centre frequency (Hz) Source: British Gypsum Impactsound

Figure 2.13 Timberfloors: Gyproc SIfloorsystem. (Courtesy

(c)

ofBritish Gypsum)

Source: British Gypsum Airborne sound insulation

48

Acoustics

in the Built Environment

Windows

Windows are the weak link element in the building envelope for shielding interiors from intrusive external noise. If noise levels are high, 6SdB(LAeq), opening windows may have to be avoided by the use of full mechanical ventilation. The various factors in the performance of the total assemblyare as follows. Thickness. Increasing the glazing thickness increases the mass and stiffness, improving performance and changingthe coincidence 'dip'. Stiffness. Toughening the glass does not affect the bending stiffnessand so has no effect on its sound insulation properties. Air space. Very small air spaces do not help appreciably (compare 6-mm glasswith 6/12/6 in Table 2.1, for example); larger spacing with differing glass thicknesses improves the insulation. Lamination. 'Platedamping'reduces the transmission ofsound througha windowby transforming resonant vibratory motion in the glass,excited bysound on the incident side of the window, into heat energy. Laminated glass comprises two thin layers of glass bonded by a clear viscoelastic material with high damping characteristics. When laminated glass is combinedwith air space and a second glasslayer in a double-glazed unit, a significant improvement in performance is achieved over a single layer of equivalent mass. Edge damping. The size of the glasspanelandhowwell it is framed has a bearing on the performanceof a curtain wall. Assuming the glazing is well gasketted, mechanical interaction between the glass panels and muntins leads to an improved soundinsulation effect for an assembly of many individual panes and muntins. Gas filling. Some insulating double glazed units are filled with argon, sulphur hexafluoride or xenon. These improve the sound insulation at higher frequencies, but below 250 Hz the reduction in performance outweighs this. As traffic noise has a strong low-frequencycomponentof noise, gas-filled glass is not beneficial compared to conventional double glazing for acoustic protection. Inner windows.Wide air spaces and decoupledframes allow good performance, although maintenance access and cleaning is a disadvantage. Separate windows can also incorporate off-set opening lights or trickle vents, without a total loss of insulation for

• • • •

•

•

•

opened lights. • Frame to masonry. Frames should be on continuous

vertedresidential properties. Thereare severalproprietary isolation systems. Concrete floors can be disappointing if the lightest-weightprecast units andnominal-onlytopping are used. Solid rather than cored units with a generous structural topping are better, achieving 48—50dB. With floors the impact soundinsulation aswellasairbornewill be ofconcern.Impactsound happens when a shortimpulsive blow to a structure 'drives' it andthe sound is carried and re-radiated elsewhere. Isolation can be given by either a

resilient surface layer, floating screed or a floating slab. Examples of the different types are shown in Figures 2.15 and2.16. The isolating layer and the slab or screed form a mass-springsystemwith alow resonantfrequency.Effective isolation is only possible at frequencies about two or three times higher than thisfrequency. Care in application is requiredas isolation battens like those illustrated have impact isolation geared to meet Building Regulations, primarily damping footfall and normal domestic activity. However, there is little static deflection inherent in such systems (otherwise there might be too much 'give' in the floor in normal use). In a recent instance of a school dance floor above other teaching rooms, the heavy impact of group rhythmical movements make the total floor system act as one, overcoming the limited deflection isolation system. Semi-sprung timber floors as developed for dance and sports surfaces, rather than systems developed for apartments, are the correct choice. The type of floor shown in Figure 2.16 is a proprietary floor by Sound Attenuators Ltd, Sunbury-on-Thames, Middlesex. Usuallyfloor-to-floorheightsare at a premium so a deep floor zone cannot be afforded. The system consists of 13-mm ply with a grid of resilient pads 50mm thick and absorption quilt between the pads. The ply serves as permanent formwork for 100mmofconcrete to be laid as the upper floor slab layer, isolated at the edges. At this 50-mm spacing ofslabs, the air gap determines the spring-mass resonance at around 15Hz. The floor is not intended as a substitute for adequateantivibration mounting of plant, as the floating floor system is only effective for frequencies above 30Hz. Another proprietarysystem avoids ply by having isolatorsjackable so that the upper slab is initially laid directly on top of the lower and then raised and levelled. The improvement given by a floating floor is such that the nett separation will be determinedby flanking effects (for example, viawallsorcolumns commonatboth levels) rather than by airborneperformanceas shown in Figure 2.16.Without attentionto the flanking routes, the average improvement in the sound reduction indexwill be limited

to around 8dB. grounds and well edge-sealed to inside and outside in order to avoid water as well as noise reveals, ingress. A weaknessoften occurs at the frame head — Sound absorption eaves closure detail, because of relative movement.

17oom

Timber floors as used in dwellings perform as shown in Figure 2.14. Between flats, Building Regulation Part E recommended detailsare a reference source [2]. The 1992 version increased newparty floorstandards, e.g. abase floor slab in a composite system is increased from 220kg/rn2 to 300 kg/rn2, and brought in onerous provisions for con-

Absorptionand insulation

Absorption and insulation are not to be confused. The application ofsound-absorbing finish to a separatingwall will not have any discernible effecton its sound insulation properties at all. All surfaces absorb sound to a greater or leser extent: bare concrete or marble have a low sound absorption coefficient, and hence absorb little sound and reflect back almost all incident energy.

50

Acoustics in the Built Environment 70 N

-J

0 Ct

C-)

aE

-a a) E

z0

'

4

10 125 200 315 500 800 1250 2000 3150 100 160 250 400 630 1000 1600 2500

x6

/ 1

2 3 4 5

(a)

6

rd octave band centre frequency (Hz) Durabella Westbourne flooringwith 22-mm battens on a 200-kg/rn2 concrete floor (b) Impact sound Figure 2. 5 Floatingtimberfloors. ((a) Courtesy of Contiwood(Durabella) Ltd; (b) courtesy ofPheonix Floors Ltd)

19mm chipboard

8mm isolating semi-rigid foam

fused to base of battens Concrete subfloor Cover moulding on mastic 19mm chipboard on hardwood/foam isolation battens Existing floor construction

•0 a) C-,

a a)

>

Absorption coefficients

Absorption coefficients are not considered dependent on the angle of incidence of sound striking the medium: randomincidence is assumed. Absorption coefficientsare normally given for the frequency range 125—4000Hz (Table 2.5). Third octave band values of absorption coefficients will not differ much from octave band values (octave bands average the third octave values, as opposed to NR values where one-third values are additive in producing octave bands); NRC and dBA are correspondingly different in derivation. Types of absorber

a) -J

10 100

125 200 315 500 800 1250 2000 3150 160 250 400 630 1000 1600 2500 4000

rd octave band centre frequency (Hz)

(1, structural floor; 2, structural and floating floor) Types of absorber include fibrous absorbers, fibrous Airborne sound insulation absorbers with impervious membrane facing, and fibrous absorbers covered with perforated panelling. An Figure 2.16 Increaseofairborne sound insulation by use of example of the first type is quilt batts mounted directly concretefloatingfloors. (Courtesy ofSoundAttenuators Ltd)

Design acoustics

51

Table 2.5 Absorptioncoefficients OBCF (Hz) 125

250

500

1000

2000

4000

0.01 0.01 0.01 0.05 0.02 0.02 0.08 0.02 0.02 0.01 0.01 0.30 0.15 0.10

0.01 0.01 0.01 0.05 0.03 0.03 0.09 0.02 0.02 0.01 0.01 0.20 0.05 0.06

0.01 0.02 0.01 0.05 0.03 0.03 0.12 0.03 0.02 0.01 0.01 0.10 0.03 0.04

0.01

0.07 0.03 0.03

0.02 0.02 0.02 0.14 0.04 0.05 0.22 0.05 0.02 0.02 0.02 0.05 0.02 0.02

0.02 0.05 0.02 0.20 0.07 0.07 0.24 0.05 0.02 0.02 0.02 0.02 0.02 0.02

13-mm 13-mm

0.10 0.75

0.25 0.70

0.70 0.65

0.85 0.85

0.70 0.85

0.60 0.80

void Metal tiles 5% perforated, 20-mm quilt overlay andvoid Woodwoolslabs

0.50 0.13 0.40

0.70 0.27 0.40

0.80 0.55 0.70

1.0

0.79 0.70

1.0 0.90 0.70

1.0 1.0 0.80

0.14

0.10

0.06

0.08

0.10

0.10

0.30 0.40 0.20 0.13 0.60

0.20 0.35 0.15 0.09 0.60

0.15 0.20 0.10 0.08 0.60

0.05 0.15 0.09 0.60

0.05 0.05 0.05 0.11 0.60

0.05 0.05 0.05 0.11 0.60

0.30 0.08

0.12 0.11

0.08 0.05

0.06 0.03

0.06 0.02

0.05 0.03

0.15

0.10

0.06

0.04

0.04

0.05

wool

0.12 0.25

0.04 0.15

0.06 0.10

0.05 0.09

0.05 0.08

0.05 0.07

air space with mineralwool

0.05

0.25

0.60

0.15

0.05

0.10

0.05 0.12

0.15

0.17 0.30 0.43

0.45

0.35 0.55 0.80

0.94

0.11

0.32

0.27

0.54

0.56 0.94

0.28

0.79 1.0 0.55 0.85 0.92 0.80

1.0 1.0 1.0 1.0 1.0 1.0

0.50 0.74 0.97 1.0 1.0 0.89 0.96 1.0 1.0 1.0 1.0 1.0 1.0

0.50 0.83 0.94

0.69 0.86

0.40 0.71 0.89 1.0 1.0 0.77 1.0 1.0 1.0 1.0 1.0 1.0 1.0

'Hard'finishes Water or ice Smooth concrete, unpainted Smooth concrete, sealed or painted Concrete blocks, fairfaced Rough concrete Brickwork, flush-pointed Brickwork, 10-mm-deeppointing Plastered walls Painted plaster Ceramic tiles Marble, terrazzo Glazing (4mm) Double glazing Glazing (6mm) Ceilings

mineraltile, direct to floor slab mineraltile, suspended 500mm below ceiling Metal planks, slots 14% free area, mineralwool overlay and

0.02 0.02 0.08 0.03 0.04 0.16 0.04 0.02 0.02 0.01

Panels

Solid timberdoor 9-mm plasterboard on battens, 18-mm air space with glass fibre 5-mm ply on battens, 50-mm air space with glass fibre Suspended plasterboard ceiling Steel decking Ventilation grille (perm2) 13-mm plasterboard on frame, 100-mm air space with glass fibre 13-mm plasterboard on frame, 100-mm air space 2 X 13-mm plasterboard on frame, 50-mm air space with

mineralwool 22-mm chipboardon frame, 50-mm air space with mineral

16-mm T&G on frame, 50-mm air space with mineral wool 22-mm timber boards 100-mm-wide, 10-mm gaps 500-mm

0.05

Treatments

Curtains in folds against wall 25-mm glass fibre, 16 kg/m3 50-mm glass fibre, 16 kg/m3 75-mm glass fibre, 16 kg/m3 100-mm glass fibre, 16 kg/m3 25-mm glass fibre, 24 kg/m3 50-mm glass fibre, 24 kg/m3 75-mm glass fibre, 24 kg/m3 100-mm glass fibre, 24 kg/m3 50-mm glass fibre, 33 kg/m3 75-mm glass fibre, 33 kg/m3 100-mm glass fibre, 33 kg/m3 50-mm glass fibre, 48 kg/rn3

0.46 0.20 0.37 0.53 0.30

0.28

1.0

1.0 1.0 0.91

0.96 1.0 1.0 1.0 1.0 1.0 1.0

52

Acoustics

in the Buift Environment

Table 2.5 Absorptioncoefficients — continued OBGF (Hz)

75-mm glass fibre, 48 kg/rn3 100-mm glass fibre, 48 kg/rn3 25-mm acoustic plaster to solid backing

9-mm acoustic plastic to solid backing 9-mm acoustic plasteron plasterboard, 75-mm air space 50-mm mineralwool, 33 kg/rn3 75-mm mineralwool, 33 kg/rn3 100-mm mineral wool, 33 kg/m3 50-mm mineral wool, 60 kg/rn3 75-mm mineral wool, 60 kg/rn3 25-mm mineral wool, 25-mm air space 50-mm mineral wool, 50-mm air space 50-mm mineral wool (96 kg/rn3) behind 25% open area

perforated steel Floorfinishes

Cord carpet Thin (6-mm) carpet on underlay Thick (9-mm) carpet on underlay Wooden floor boards onjoists Parquetfloor on timberjoists and deck Parquetlaid concrete Vinyl or linoleum on concrete Vinyl and resilientbacking on concrete

125

250

500

1000

2000

4000

0.43 0.65 0.03 0.02 0.30 0.15 0.30 0.35 0.11 0.34 0.10 0.50

0.97 1.0 0.15 0.08 0.30 0.60 0.85 0.95

1.0 1.0 0.50

1.0 1.0 0.85

0.60 0.95 0.40 0.70

0.95 1.0 0.96 1.0 0.70 0.90

1.0 1.0 0.80 0.60 0.80 0.90 0.85 0.92 0.94 0.82 1.0 0.90

1.0 1.0 0.80 0.90 0.75 0.85 0.85 0.85 0.82

0.87 1.0 0.90

0.86

0.20

0.35

0.65

0.85

0.90

0.80

0.05

0.05 0.09 0.08

0.10 0.20 0.30 0.10 0.10 0.07 0.03

0.20

0.04

0.05

0.45 0.70 0.75 0.06 0.05 0.06 0.04 0.05

0.65 0.72 0.80 0.07 0.10 0.07 0.05 0.10

0.69 0.98 0.45 0.43 0.61 0.89 0.88

0.81 0.45 0.45 0.58 0.82 0.82

0.78 0.87 0.45 0.45 0.50 0.70 0.70

0.96 0.93 0.50 0.005 0.005 0.005 0.45

0.93 0.87 0.40

0.85 0.80 0.20

0.01 0.009 0.009 0.60

0.04

0.03 0.08 0.15

0.30 0.60 0.90

0.02

0.11 0.15 0.04 0.02 0.02

0.16 0.24 0.33 0.15 0.40 0.44 0.49

0.24 0.40 0.40 0.38 0.50 0.60 0.66

0.56

0.60 0.27 0.80

0.74 0.53 0.70

0.88 0.67 0.60

0.20 0.04 0.02

0.54 0.60 0.07 0.10 0.06 0.04

0.80 0.75

0.90 0.90 0.90 0.92

1.0

0.80

Miscellaneous

Audience on timber seats (1/rn2) Audience on timber seats (2/rn2) Audience per person, seated Audience per person, standing Seats, leather covers (per m2) Upholstered seats (per m2) Floor and upholstered seats (perm2) Areas with audience, orchestra, or seats, including narrow aisles

Orchestra with instruments on podium, 1.5 m2/person Shading factor (apply to finishes under seats, x coefficient) Air 30% RH (per m3 at 20°C) Air 50% RH (per m3 at 20°C) Air 70% RH (per m3 at 20°C) Office furniture (perdesk)

0.50

0.40

0.78

0.44 0.42 0.58 0.77 0.80

0.45

0.96

0.03 0.02

0.70

Valuesexceeding 1.0 have been roundeddown to 1.0.

on a wall surface, or carpet on a floor. An example of is 5% or less, the panels are reflecting except for the third type is metal perforated suspended ceiling myriad Helmholz resonators formed by the holes. 'Bass tiles with quilt inlay above; provided the open area of traps' are used in studios to provide broadband absorpthe perforations exceeds say 20%, the quilt and air tion right down to very low frequencies. They consist of cavity behind the metal tiles is almost as efficient at a lined labyrinth air space within which negligible soaking up sound as if the tiles were not present. In reflection results. An extremecase of absorptive materials installation is studios, deep boxes with thin membranes can be puror selected to even out the reverberation the semi-anechoic and anechoic chambers in acoustic pose-designed characteristics at different frequencies. Resonance laboratories (Figure 2.17): deep wedges of foam above, absorption can be produced by selecting appropriate below andto all sides reduces the reverberation time to a perforation and air space depth. If the perforation rate very low value at all audible frequencies.

53

Parallel pattern

II

—1

(1/rn2

Figure 2.17 Anechoü chamber 1-

4 Cross pattern (1/rn2)

A featureof absorption is that the more that is put into a room, the less effective it is, because new absorption is 'competing'with the absorption already presentto absorb incidentsound. The maximum absorption effect is in a

diffuse field,i.e. whensound is incident on the absorptive material from all around. There is also a slight 'drawing in' of sound at the edges. For a specific area of surface absorption in a room, the maximum absorption effect is obtained by distributing small areas all around.

2

Reverberant soundpressure level

The reverberantsound pressurelevel is given by:

L=SWL—lOlogA+6+lOlogN where SWL is the sound power level of a noise source within the space, Nis the number of sources, and A is the absorption present. As 10 log 2 is 3, it may be gathered that each doublingof the absorption in a room reduces the reverberantSPL by 3dB.

0.9

0.8

Reverberation time

The reverberation time is the finite time it takes for the sound source energy in a space to decay 60 dB when switchedoff. For enclosures in which a diffuse sound field existsandwhere the average absorption coefficient is less than0.1, the reverberation timecanbefoundbytheSabine Equation. Where the average absorption coefficient is greaterthan 0.1, the Norris-EyringEquation can be used. Both methods are described in Chapter 5. Air absorption effectsmustalso be accounted for in larger volumes.

C 0.7 C.)

U)

00

0.6

C

0 0.5 0 .0 0.4 0.3

Largerspaces 0.2 Larger spacesproducesound decay characteristicsin poor with Sabine or In agreement Norris-Eyring. 'amorphous 0.1 space' areas, such as shopping malls or industrial halls, thereisnot atrue reverberant fieldacross thespace and the sound characterwill vary in different parts ofthe space. On 0 theother hand,suchspacesare not 'free-field' and the SPL 125 250 500 1000 2000 will decay at something less than 6dBforeach doubling of Octave band centre frequency(Hz) distance from the source. Empirical data suggest 4dB/ 1 parallel pattern doubling of distance across typical industrial halls. Alter2 cross pattern native forms of calculation have been proposed for industrial halls. Complex spaces can sometimes be sub- Figure 2.18 Overheadsound absorbers. (Courtesy of divided into individual coupled volumes: if alcoves off a Rockwool)

4000

54

Acoustics in the Built Environment

electret/capacitormicrophones. There are a number of computer systemswith powerful graphical presentations, emanatingfrom Japan, USA and Europe. Other systems are suited for sound systems design, having been developed by internationalsound equipmentmanufacturers. Ar X S A room acousticsmodelling programshould allow basic A= evaluation of rooms of any shape and complexity. The Ar + S calculation methods are intended to combine the best of where A is the absorption contributionfrom the recess to both ray-tracing and image-source methods. Desired the mainspace, Ar is the absorption in the recess, and Sis features in such a programare: the area of the openingbetween the recess and the main fast estimation of room volume and reverberation mainspace have significantabsorption suchthatsignificant energyis notreturnedintothe mainspace, the surface area ofthe alcove openingcanbe countedas a = 1. Alternatively, a simplified calculation is given by:

space.

Finishes

Finishes, then, can be designed to affect room acoustics in three different ways: absorption, reflection and diffusion. Absorption

•

conditions

• reflectograms with 'sound rose' graphical displays • 3D tracingof individual reflection paths • maps of energy parameters over chosen surfaces • fast recalculation in response to altering receiver and

materials

absorption • position easy operation: menu-driven, warnings, and data • displays project file management which allows consistent and records of the

Absorption can either be integral in a space (e.g. by virtue of blockwork faces or a suspended ceiling) or added as a design analysis thorough decorative finish (carpet, wall linings, curtains and furniapproach ture), and then, of course, there are the occupants. multiple source capability Absorption is more effective spread around rather than compatibilitywith CAD systems concentrated all in one area. Some elements show the source directivityfactors 'perfect' absorption coefficient 1; 'space absorbers', hanglink to audible simulation of acoustic conditions ingbafflesorbannersare absorptivelyparticularlyeffective RASTI map calculation because they soak up incident sound from both sides. In industrial premises,arrays ofoverhead absorbers, one per ODEON, a system derived for acousticians by the of Copenhagen, is an example of a program can be used to soak levels of metre, up high process University square that includes a number of the above features, although noise in bottling plants orprintinghalls (Figure 2.18). there is no one ideal system for all purposes. Figure 2.19 shows the use of ODEON for remodelling the Royal Reflection Reflectionofsound atsurfaces notabsorptivein naturenot Albert Hall, London, contrastedwith physical modelling. only increases the reverberant sound level but also directs Figure 2.23 shows an ODEON CAD model used by Arup the sound to other surfaces. Rooms of particular propor- Acoustics on the new Bridgewater Hall, Manchester. The tions can give cross reflection effects, impairing speech geometry of a room is typically defined by coordinates for intelligibility. Curved walls can focus sound, and by so its corners,plus cornersto surfaces within. AcousticsCA]) doing starve other parts of a space of sound. Strong models typically comprise perimetersurfaces, the size of directedsound is afeaturedesiredbymusicalperformance individual surface files being not less than a couple of audiences inmodern hallsbut this has tobecombinedwith square metres, otherwise edge effects render analysis less diffusion; the methodsofproviding adequatesurface area accurate. Curved surfaces have to berepresentedas facets. Other systems for auditoriainclude Renkus-Heine's Elecare discussedunder 'Concerthalls'. tro Acoustic Simulators for Engineers (EASE) acoustic modelling software, and Swedish acoustician Bengt-Inge Diffusion Diffusion is an effectwhereby the complexityof reflecting Dalenbãck's Computer-Aided Theatre Technique (CATT) surfaces results in an even dispersion of sound in a room: -Acoustic. The latter can import files directly from the modelling of reflecting surfaces can ensure this by AutoCAD. Any system should be validated to 'stock' breaking up incident sound. In order to break up low auditoriawhich have known characteristics, for example frequency components of sound as well as middle and the RoyalFestivalHall, or to physicalmodelstestedin the upper frequencies, the modelling ofsurfaces has to be on laboratory, a technique which has proved comparatively a large scale, e.g. projections exceeding 300 mm and reliable in the past. The latest tool to demonstrate conditions is auralization, whereby a CAD model is element areas exceeding 0.5 m2. detailed enough to allow orchestral set-pieces to be heard Auditoriamodelling as if in the real hall at a specific seatlocation. For auditoria modelling of interiors considering the effects of sound-absorbing or sound-reflecting surfaces, there is a choice between physical and computer predic- An example of CAD and physical modelling tion techniques. Physical models (1:50 or even much larger scale) are still the most reliable for the most TheRoyalAlbertHall, London important projects, e.g. major concert halls, with wave- A £58m refurbishmentwill include the interior remodellengths scaled up accordingly, spark sound sources to ling of the 1871 5500-seatceremonial hall (Figures 2.19a, produce the high frequencies needed, and miniature b, and f), to tame the famous echoes for orchestral and

• • • • •

Design acoustics

55

(b)

(d)

(f) Figure 2.19 Sound decay analysis: ODEON ampiffied music events: these included stalls examples of +3dB on direct sound after 300 ms time delay. A fabric velarium was the original means of acoustic control, removedin 1949. The replacement suspensions were 102 grp 'mushrooms' at 25 m height and a cumbersome orchestral canopy at 11 m height, installed in 1969.

Initial investigation, by BDP Acoustics, consisted of extensive baseline measurements at 14 receiver positions andtwo source positions, for unoccupiedhall andduring events. Results were validated to an ODEON model (Figure 2.19e). Balcony seating with tiering — existing and proposed— werelaboratorytestedprior to installation and remeasurement in the hall.

56

Acoustics

in the Built Environment 90 14

80 -O

12

w C.)

70

a,

i

+

0 60

-:

50 C Co

1Z

1H

I: I 1 1

U,

5

5 40

30 125 200 315 500 800 1250 2000 3150 100 160 250 400 630 1000 1600 2500 ,rd octave band centre frequency (Hz)

Sound Insulation between typical auditoria

Figure 2.20(b) Multiplex cinemas: sound insulation between typical auditoria

Since mid-1996, acousticians Peutz & AssociésBV have studied the Hall's behaviour in a walk-in 1:12 physical scale model 3.6m high and 5.5m long (Figure 2.19c). The acoustic 'evolution' of the Hall has been re-created, Figure 2.20(a) Multiplex cinemas: Separating walls— including the original dome profileand the mushrooms. section. (Courtesy of UCI(UK) Ltd/BDP) New solutions are being developed to give back the visual character whilst improving, or at least 1. 13-mm plasterboard on 13-mm plywood (for ease of cable original a practical modern acoustic quality. maintaining, in fixing projection room) Measurements were taken using microphones in the 2. 146-mmmetal studs, beddedin acoustic mastic at wall ears of 1:12 'Barbie' dolls, to auralize the various interior boarding 3. 50-mm glass-fibre quilt cavityinlay configurations by interpreting the binaural impulse re4. 2 X 13-mm plasterboard, acoustic mastic andjoint taping sponses as a modification ofanechoically-recorded music at corners andother signals. 5. 2 X 15-mm plasterboard, lappedjoints, face joints taped and filled 6. 100-mmglass-fibre quilt Criteriafor differeivtbuilding types 7. 2 X 92-mm metal studs at 600-mmcs 15

8. 50-mm rock fibre bans, black tissuefaced, as absorption

behind screens

9. 50mm X 50mm timber batten beddedin acoustic caulk 10. Blockworkinner leaf to outside walls: structural break at

separating wallswhere possible 11. 2 X 92-mm metal head studs fixed to metal plate at underside of tie beam 12. Double angles at head to allow up to 25-mm roof deflection/uplift without losing acoustic integrity 13. 40-mm Vicucladbedded in acoustic mastic and with profiles packedwith mineralwool 14. Built-up chippings/feltroofing! thermalinsulation on metal decking 15. 2 X 92-mm metal base studs and plasterboards bedded in acoustic mastic 16. Bracing to separate studs at max. 3500 Cs. support to quilt by 25 X 25 metal angles running between studs

Cinemas

Multiplexes

Multiplexes are a new form imported from the USA, involving typically a group of auditoria with a common projection room and concourse/foyer. Often new developments are 8- or lO-plex but versions ranging from 3- to 24-plex have been attempted. The key design issues are sound insulation between auditoria, isolation to outside, good soundsystems, 'dead' room acoustics,andmoderate ventilation noise. Adequate separation can be provided (DflT, 65—70+ dB has been achieved on 10 such projects to date by BDP Acousticsfor UCI (UK) Ltd, Manchester) by as low a specification as two layers of 15-mm plasterboard on separate studs, significant cavity with 100-mm quilt inlay, and careful head, base and edge detailing

57 PROJECTION

ROOM

2

3 4

dB 65—74

(variance over 10 projects>

Figure 2.22 Odense concert hall, CarlNielsen Hall

There are more sophisticated sound systems, for exampleTHX, which are moredemandingon sound insulation between cinemas (masonry wall added between the separate studs) and low ventilation noise levels (NR25). IMax, OMNI and MotionMaster cinemas require specialized attention including vibration control to some of the cinematic effects. Conversions

liii iii I II

0

100

I

200 mm

Figure 2.21 Multiplex cinemas:separatingwalLc —plan (see Figure 2.20for key). (Courtesy of UCJ (UK) Ltd/BDP)

Conversion of older theatres and cinemas results in satisfactoryresults, althoughit is less common now. Multiboard dry construction linings to form, as far as possible, separate auditorium 'shells' is important; concrete rather than timber floors should be used. Results will not be as good as for a purpose-built multiplex because offlanking via the existing walls; DflT, achievable may be around 55dB. Concert halls

Concerthalls requirespecialistdesign advice so only a few principles are offered: the acoustics can be made to work (Figures 2.20 and 2.21). Research and investment by for a number of differentgeneric hall types. suppliers, for example British Gypsum Ltd, has led to a proven range of high-performance assemblies [51. The Hall shape head detail to a lightweight roof is a problembecause of Hall shapes can vary from the traditional 'shoebox' and roof deflection effects either buckling the partition or coffin-shape halls, to geometric halls. 'Shoebox' halls causing a gap; this is overcome by a closure angle have enjoyed a renaissance, as offering good cross reflection characteristics between side walls. They put the movement joint. Outside noise will come in via escape doors (these audience centre-front to the orchestraas far as possible shouldbe 40+ dB rated,light- and sound-proof), orviathe for the best sound blend. Recent examples at Dallas and lightweight roof. The surface mass ofthe roofmay have to Birmingham are attracting publicity.The problem is that be uprated or a barrier ceiling included ifthe multiplex is the admired nineteenthcentury shoebox halls like Musidirectly under a flight path or close to an elevated kvereinsaal,Vienna, are by modern standards only recital motorway. Individual entrances into auditoria should be hall size. Even a hall like the 2206-seatConcertgebauw, by acoustically rated (30+ dB) doors in lobby configura- Amsterdam, would be much larger if replanned to tion. Some ventilation noise (NR 35) is welcomed as it current standards of safety and seating. For a full-sized masks residual intrusive noise from the adjacentauditoria concert hall (2000—2500 seats) to suit a full orchestra soundtracks andaudience sounds. The standardsystem is and choir (up to 120 musicians plus 250 singers) the a dedicatedunit to each auditorium with ducted supply arrangementcan lead to a large template — Birmingham and extract via the ceiling void. In some leisure centres, is over 60 m long and has a very generously-sized cinemas are located above or below noisyfacilitieslike ten- platform focussed in amphitheatre style on the conpin bowling and discotheques; tenancy agreements on ductor's rostrum. Shoebox halls do however still work maximum sound levels and double floors are required to well for lesser occupancies, as Jordan Akustik's 1377-seat avoid operational difficulties. Odense hall testifies (Figure 2.22). Some concert halls

58

Acoustics

in the Built Environment

Figure 2.23(a)—(d)

The BridgewaterHall, Manchester

are not even axial to the platform: Aalto's concert halls put more seating on the 'keyboard' side of the piano soloist; Segestrom Hall, Orange Free State, California, interlocks two narrow halls as a means of avoiding the disadvantages of fan-shaped auditoria. In the UK there are impressivenew semi-surround major concert halls in Manchester (Bridgewater Hall) and Belfast (Waterfront Hall). Figure 2.23 shows the 2400-seat Bridgewater Hall during design and at completion. Figure 2.24 gives similar coverage of the 2250-seat Waterfront Hall. Reference can be made to a number of case study collections,for example AcousticalSurvey ofElevenEuropean Concert Halls [61

and Halls for Music Performance: 1962—1982 [7]. Excellent recent works are Beranek's Concert and Opera Halls: How They Sound [8], Barron's Auditorium Acoustics andArchitecturalD [91, andAndo and Noson's iVlusic and Concert Hall Aoustics [10].

Seating

Seating is a key issue as there are so many constraints — sightlines, travel distances, aisle steps, seats per row and balance of seats at different tiers. 'Vineyard' seating as pioneeredat the Berlin Philharmonie workswellin milder form: 'seating trays' of several hundred can be optimally set to face the platform and have local side-reflecting surfaces (Figures 2.25a and b).

Table 2.6 Optimum volumesfor performancespaces

n

Theatres Rooms for speech The volume should be adequate for a full-bodied sound: Opera houses the old rule of 'RT X 4 equals volume per person' is if Concerthalls anythingon the low side and 10 m3 per person even in a Churches full-size hall is advisable (Table 2.6). Volume

Optimum volume (m3/occupant) Minimum 2.5 —

4 8 6

Recommended

3 3 5 10 10

Maximum

4 5 6 12 14

Design acoustics

59

(f)

Figure 2.23(e)—(g)

The BridgewaterHa14 Manchester

Reverberationtime (RT)

Reverberation time is still a fundamental measure in concert hail design although in recent years design concern has extendedto not only RT but also to the ratio ofearly to reverberantenergy and to lateral efficiency, i.e. the adequacy ofearly lateral reflections. A strong, precise and clear sound is the current taste; live music that is expected to match the quality of the living room CD player. The approachneedsgreat careas, ifreflections are too strong, tone colorations to sound quality can result. There may even be a loss of reverberance if significant sound energy is directedstraight to absorbentoccupants

classical,symphonic, choral, and organ music. The Halle is its resident orchestra. Other performance types will utilize the house high-quality sound reinforcement systems.

Thegeometry ofthe auditorium, conceived and refined jointly by Arup Acoustics and Renton Howard Wood Levin, is a synthesis oftwo concerthall geometries known to provide excellent symphonic sound, the 'shoebox' and 'vineyard' forms (Figures 2.23b and 2.23d). The volume, 24000 cubic metres, was determined by the target midfrequencies reverberation time of 2s. The designdeveloped usingboth CADandphysicalscale and seating. models. The ODEON model (Figure 2.23a) had 500 surfaces defined, with over a third ofa million acoustic ray paths calculated and analysed. The 1:50 scale model Two recentexamples (Figure 2.23c) was used to look at acoustic parameters, applying MIDAS software, for ray tracing using a laser The Bridgewater Ha14 Manchester sourceandcalibrated mirrorsystem, for volume estimates The 2400-seat hall was designed and built without byinfill technique, andas a visualizationaid to the design compromise to be excellent for the performance of team.

60

Acoustics in the Built Environment

(a)

(b)

(d)

(c)

Figure 2.24(a)—(d)

The WaterfrontHall, Belfast

Building services and lighting noise were designed to PNC 15, with main plant in an isolated tower (Figure 2.23e). The entire 25000-ton concert hall is supportedon 280 steel springs to prevent disturbance from adjacent Metrolink tranis, External noise break-in is minimized by wrapping the ancillary accommodation around the auditorium. Where the auditorium rises above these buffer

zones, there are massive twin wall and roof structures to exclude noise (Figures 2.23fand 2.23g). The WaterfrontHall, B4fast

The 2250-seat elongated hexagon concert hall results from a collaboration of acousticians Sandy Brown Asso-

Design acoustics

WATERFRONT HALL

AUDITORIUMLOWER CIRCLE

(e)

WATERFRONT HALL

61

AUDITORIUM UPPER CIRCLE

(f)

AUDITORIUMSECTION 0

IOU

(g) Figure 2.24(e)—(g) The WaterfrontHall, Belfast

ciates, with architects Robinson and Mcllwaine.A largevolume reverberant space has evolved from St David's Hall, Cardiff, in arrangingseating trays for good diffusion and local soundreflections. Overhead reflectors, galleries, and platforms provide local reflections for performers, to assistensemble andbalance. Early use of a 1:50 physical scale model led to design modifications and further testing. Flexibility of use is accommodated by removal of stalls seating to allow a central arena format, and acoustic adjustment by the movement ofhigh level areas offabric. The fabric reduces reverberation timesfor events where speech intelligibility or amplified music are the main consideration. Ancillary accommodation — foyers, dressing rooms, offices— cocoon the auditorium from external noise. The

roof comprises two concrete slabs, the outer domed to form a significant void between the slabs.

A displacement ventilation system includes very low air velocity supply air via special terminals under the seats. Special flexible bellowsintroduce air to stage elevators to accommodate the range of elevator movement. Early objective measurements and subjective tests indicate an excellent acoustic for orchestraluse, a warm wellbalanced yet intimate sound. Further acousticparameters Early decaytime

The early decay time (EDT) is the most important criterion in evaluating a hall's acoustics, followed by

62

Acoustics

Figure 2.25(a)

in the Built Environment

Vineyardseating: Berlin Philharmonie (Sharoun Main Hall)

Figure 2.25(b) Seating trays: Berlin Philharmünie (morerecently built Recital Hall)

Design acoustics

Figure 2.26(a) and (b) Hall, New Zealand

63

Directedsound: Wellington Town

Lateral Efficiencyand Clarity. The EDT should not differ from the Sabine RT more than ±10%; for a concert hall, values between 1.8 and 2.3s should be sought. It is the decay time measured over the first 10dBofenergy fall-off, equivalent to the slope of energy curve measuredwithin the first 500 ms. Due to the nature ofmusic performance the final part ofthe sounddecay ofnotes is seldom heard. The later part of the reverberant decay from a specific impulse (transient) is masked by subsequent signals after approximately 10dBofdrop, i.e. peaks in music performance only rise about 10 dB above the average level during that passage. EDT involves measuring the first 10 dB of decay and multiplyingby 6 to correspondto RT values.As EDT is sensitive to room geometry, in particularto strong early reflections to reinforce sound in the first 100ms, the EDT will vary with location around a hall (see Chapter5). In huge halls, the EDT can vary spectacularly, highlighting the remoteness ofsurfaces: the Royal Albert Hall, London (86 650m3), has in its stalls EDTs of 1—1.25s compared to Sabine RTs of around 2.5 s, across middle frequencies. Ratioof early-to-late energy The ratio of early-to-late energy is the measure of the balance between clarity and reverberance in music; different types of music, for example Romantic compared to Mozart, suggest different balance values.

64

Acoustics in the Built Environment

Early lateral energy fraction

The early lateral energy fraction defines the relationship between a sense of spatial impression or envelopment for the listener and the arrival of reflected sound from sidewalls relative to the listener. It is the fraction oflateral energy arriving between 5 and 80 ms after the arrival of directsound compared to the total sound energy arriving at the listenerwithin the first 80 ms ofdirect sound arrival. The maximum values found in auditoria are around 0.3. D50, C50 and C80

Other measures areDeutlichkeit (D50), Clarity Index C50 and Clarity Index C80. D50 derives from the ear's response to consecutive impulses. A sequence of sound impulses delayed more than 50ms is perceived as discrete impulses, whereas those with less delay combine to enhance the loudness of the impulse before. Good auditoria will have higher D50 values. C50 is slightly differently calculated and is presented in decibel form with values greateror less than 0.5 appearingas C50s with positive or negative values respectively. For a speechorientated hall, positive values of C50 are desirable. C80 uses the limit of perceptibility 80 ms to suit music uses, again in decibels. Positive values resultin a crisp acoustic suitable for classical music andsome operatic use but will not provide a suitable setting for romantic and choral works which are enhanced by a greater reverberance. Directed sound

Directed sound has become an issue in acoustic design. Marshall incorporated the idea of supplying early lateral energy when he was appointed acoustic designer for a concert hall in Christchurch, New Zealand, in 1972. The lack of lateral reflections at centre seats due to the hall width is compensated for by an array of large reflector panels suspended overhead angled to direct sound into central seats deficient of lateral sound (Figure 2.26). Schroeder-designed reflector panels used in the 1983 Wellington Concert Hall by Marshall are based on a repeated'Quadratic Residue Sequence'ofdifferentdepth wells along the panel surface. Interference due to the pattern selected contributes to a wide diffusing area (Figure 2.27b). Theconceptofusingother reflecting surfaceswithin the auditorium was also used by Cremer in the innovative Berlin Philharmonie; other hallsin whichCremerhas been involved have incorporated 'stepped hexagons' in which seating is split into hexagonal stepped terraces which provide all seatswith localizeddirecting surfaces.Even seat backsto rearmostseats can play their part (Figure 2.27a). Musicians

Musicians as users have specific needs and the priorities are slightly different to those of an audience. The Musicians' Union stresses the followingneeds: reverberation time (full-bodied); variability (not altered by occupancy); dynamic range; frequency response (balance of sound, no orchestral section or pitch band receiving overor under-emphasis); clarity and separation (between solo instruments and sections). In addition, on the platform there should be integration (sound similar to that perceived in the auditorium),ensemble (ease of hearing between sections), and floor response to instruments.

Ventilation

Ventilation in halls can serve both energy-efficientlyand quietly by underseat supply and overhead extraction (Figure 3.11 type 2). As exposed ductwork at a high level in halls presents an unpredictable source oflow-frequency absorption and duct-noise breakout, its presence in the hall shouldbe minimized or set behind an acoustic 'shell' ceiling. A sensible approachto adoptinga criterion is NR 20 for concerts, andan assured NR 15/PNC15 maximum for broadcasting/recording. Multiuse

Multiuse is a fact of life, even for halls with resident orchestras. Choirseating can be on bleachers extendinga platform back for conference use, seating to the immediate sides can be on towers to be removed to form 'wings'. Stage lifts can alter the configuration for different music settings, dropping to form an orchestra pit for opera. Acoustically, banners can drop within the hall to reduce the reverberation time by up to 15%. This will improve speech intelligibility in the hall. Overhead acoustic 'clouds' to help the orchestra maintainensemble can be flown aside to enable sets or a projection screen to be dropped. Back projection, simultaneous translation, projection room and control rooms will help the operational efficiency. In a number of halls, large acoustic canopies slungover the platform are claimed to adjust the acoustics for different sized events. Multiuse halls are a design challenge and the most demanding use in design criteria terms may only be a prestigious occasional use, so it is realisticto have the most frequent use as a base setting with means of altering conditions for other events.Reverberant sports or concert halls can be made deaderfor dramaby droppingbanners or drapes, small halls or dead halls enlivened acoustically by electronic means. Figure 2.29, Diagram 2.5 and Table 2.7 list some typical events which can crop up: these cluster to particular settings (flat floor, etc.) although inevitablythere are varying requirements within headings, for example 'classicalmusic' can meanconditions ranging from 1.2s for chamber music to 2.5s for majorRomantic and choral works. Courts

Acoustic attention centres around the courts themselves, as theywill have to be isolated from other areas by sound lobbies, acoustic doors, and50+ dB walls. Ventilation noise levels shouldbe kept to between NR 30 andNR 35. Good conditions are important as close concentration is demanded over long sessions. To keep out intrusive noise, perimeteraccommodation as well as the courts may have to be mechanically ventilated. Floors under courts and over cells should be 50+ dB, e.g. 200-mm concrete slab plus 50-mm topping (concrete waffle with thin minimum slab thickness or hollow precast units should not be used). Plant rooms should be kept remote from courts. Some rooms with specific needs, as identified in Home Office Room Data Sheets, are identified in Table 2.8. The natural acousticsofa courtroom should allow good speech intelligibility.To some extentthis is engenderedby the reinforcementof direct sound from the speaker by early reflections which combine with the direct sound to

65

QUADRATIC RESIDUE SEQUENCE

!

I

—

j

I

I

I

I

I

I

THICK BANNER DROP

ZONE

GRG

I'

III

(a)

(b)

II

4

t

Figure 2.27 Concert hail detail.: (a) high-backseats at rear; (b) ceiling reflectors; (c) side-wallabsorberbanners

66

(c)

Acoustics

in the Built Environment

Figure 2.28 Acoustic model testing: (a) Linköping Concert Ha14 (b) GlyndebourneOpera House, (c) Segestrom Hall (California) and (d) WycombeEntertainments Centre (also shown in Figures 2.40and 2.41)

Design acoustics

• •

Public meetings: political, religious Pop festivals

D

• •

I

S Snooker, darts, wrestling, swimming, ice-hockey, skating

I .E • E

•

I I

a,

a) C

C5) Wa,

Trade shows Exhibitions Dances Banquets

Ca

E

2

Spectator sports: cricket, rugby,football Participation sports: running

I

•

c

•

•

o

I I

•

j

I I

I

•

I I I

I

Cinema Conferences Pop concerts

Theatre Staged musical events Ballet Opera TV studiotheatre Classical concerts Choral Chamber

— __I

•

BBC ILR (IBA)

Recording studios

Diagram 2.5 Publicperformance spaces Table 2.7

0Z

Recommended mid-frequencies reverberation times

Activity

Broadcast

RT 0.2—0.25

0.3 L0—2.0

Speech

0.6—1.2

Drama

0.9—1.4

Amplified sound

0.5—1.2

Multiuse

1.0—1.7

Opera

1.0—1.6

Soloists, ensembles

1.2—1.7

Orchestral music

1.7—2.2 2.0—5.0

Organ and choir music

te

Building

Sound dubbing, announcerbooths Small speech studios Large classical music studios Council chambers, law courts, lecture theatres, meeting rooms, conference halls Theatres, functionrooms Multiplex cinemas, pop concert venues, discotheques, videowall settings School assemblyhalls, community halls, sports/arts halls Opera houses, theatres with orchestrapits Recital halls, orchestra rehearsal halls, chamber music salons Concert halls Ceremonial halls, organ concert halls, churches, cathedrals

67

68

Acoustics in the Built Environment

a strong signal. Late reflections (arriving much after 30ms) are however counterproductive as they blur the original message. The desired finishes will therefore be limited local sound reflective surfaces combined with sound absorption to other surfaces: floor carpet (this will damp impact/footfall noise as well as provide general absorption), selectivewall linings and ceiling treatments. To achieve these target values local treatment will be required behind and to the side of the public gallery to absorb intrusive visitor noise,and to the side of the bench, where the confidentiality of whispered briefing needs to be maintained. The important parts for the maximum audibility are witness box to jury, witness box to judge, counseland dock tojudge. Proceedings audibility to the public seating area is a slightly lesser priority. PSA and Home Office guidance advises as a suitable setting for court activity, that the reverberation time calculated for the furnished room shall be 0.8s at 125Hz falling to 0.6s at 250 Hz and continuing at 0.6s for frequencies up to 4000Hz, with tolerance on these values provide

(C) (C)

E

0 CD

(C)

.0

> CD CD

±0.15 s.

0.05

0.1

0.5

5.0

1.0

10.0

Room volume (x 1000) (m3)

timesfor dfferentspaces. Figure 2.29 Reverberation (Courtesy ofSoundResearchLaboratories, Cokhester Essex)

As far as possible, good natural acoustics should be relied on for proceedings. Thejudge and counsel will be usedto speaking clearly and addressing the court. Speech reinforcement may be considered, however, to reinforce speech from the witness box, particularly to the public galleries at the rear ofthe courts. Security enclosure ofthe dock in some courts may impede reception of speech from this source, so here too speech reinforcementmay be considered. The systemshouldbe high quality andfree from audible hum, noise anddistortion. Discotheques

The attraction ofdiscotheques is precisely their noise and freneticactivity. The problems associated are noise breakout to neighbouring properties, hearing damage to employees,andstructurebornere-radiated sound to other facilities in the same building. Average sound pressure Table 2.8 Specific needs ofcourts and surroundingrooms levels on the dancefloor climb to the range 90—llOdBAas the night goes on, with a high component of low Good include frequency sound. Levels tend to be 8—10dBA higher by sound the endofthe disco session. Where amplified live music is sound insulation absorption performed,levels can be even higher. Such sound power levels exceedclassical forms ofmusic — orchestras in loud passages maybe a more modest80 dBAorso. The Code of Main courtrooms Juvenile courts Sound lobbies Magistrates' retiring rooms Court hail Duty solicitor's room Social workers' offices Holding/waiting rooms Internal circulation Clerk to the justice's office Deputy clerk's office Secretary's office Legal/administration/accounts areas Public zone — counter Interview rooms Consulting rooms Refreshments area

•• • • •• ••

•• •• • •• • •• •• ••

Practice on sound levels in discotheques [11] identifies the hearing risk for staff in particular. The Code recommends an LAeq not to exceed 100dB at the nearestpoint in the premises to operating loudspeakers, the value referred to as the Maximum Permissible Exposure Level. It assumes 25% of the total public area is given to rest areas, otherwise a MPEL of 95 dB would apply. It is not desirable to have direct-to-earsound, diffuse andreflected sound being better to even out exposure. Previous GLC guidance recommended an LAeq,8h not exceeding 93dB, or for external audience protection 93dB at 50m. Discotheques are an obvious candidate for assessment against the Noise at WorkHSE statutoryguidance [12]. In considering an Entertainments Licence, any authority will consider the following:

• objection at any public hearing • duration and timing of concert

Design acoustics

• frequency of concertsat the same premises • noise complainants at previous concerts • location (in relationto noise-sensitive buildings) Noise-limiting devices on sound systems can be included although commercially it is not realistic to set values below 90dBA. Premises should have full mechanical ventilation (direct-to-atmosphere extracts with no attenuationwill in most cases be unacceptable because of the impact on the environmental noise climate) and lobbied doorset accesses at the entrances. Re-radiated structurebornesound demands great care in design, one approach being to isolate the disco walls by— using a drylining 'shell' and effectivelya triple floor a dance floor on a concreteslab on isolators on a secondconcrete slab — to alleviate the problem on the floor below. Education buildings

Draft revised Building Bulletin 51 Acoustics in Education Buildings [13] and Design Note 17 [14] have yet to materialize in final form. Design Note 25 Lighting and Acoustic Criteria for the Visually Handicapped and Hearing Impaired in Schools [15] can be referred to for those with special needs. BS 8233 [161 classifies four groups with sound insulation requirements varying from 25 dB to 45 dB. Classroomconditions should be controlled to 0.75 s at middle frequencies and 40dB average separation between reading areas. More importantly, overhead ceiling surfaces can usefully be sound reflective if side and rear walls are panelledin saypin boardingto dampsoundblurringcross reflections. General mechanical ventilation shouldbe designed to within NR35 in teaching rooms. In primary schools in particular, openingdoors and windows from classrooms are expected, so a consideration of facade aspectwill avoid distracting external noise levels. School theatres are no longer exclusively an adaptation of the assembly hall but mimic public theatres. A reduction in scale, including platform height and size allows for the lesser projection ofchildvoicescomparedto adult. Health buildings Noise control rather than room acoustics is important. Hospitals are highly serviced and reference to Building Notes, Technical Memoranda, Health Circulars and Hospital Data Sheets should be made. Recommended design criteria are shown in Table 2.9, as a more detailed interpretation to rating values included in Chapter 3. Separation between rooms has to be carefullyconsidered given the requirement to stop most partitions offatceiling level.

69

busy roadsor airports, or in city centres. The main issues will be noise break-in from outside, privacybetween rooms and to public rooms, and ventilation noise. Windows

Windowsin hotels have openinglights even in the noisier situations; good weatherstripping and double glazing are essential. Some protection to road noise can be given by inset balconies. Privacy

Privacybetween rooms will be of a reasonable standard if separating walls and floors are selected with an average SRI of 50dB (for example, plastered 200-mm dcm, blockwork and solid precast concrete floor units with structural topping). Creation of a lobby outside the en suitebathroomwill give isolation to corridor noise. Crosstalk attenuation to bathroom extracts will prevent this being a route for plumbingsounds. If single doors from corridors are used, these should be 35-dR rated, i.e. solid core plus seals, well rebated. Bathroom — corridor walls should have an average SRI of 45dB. Partitions must extend full height, structural floor-to-floor, and weaknesses like back-to-backelectrical sockets mustbe avoided. Room televisionandradio sets shouldnotbe fixed directly to the room separating walls. Ventilation noise

Ventilation noise should be kept within NR 35 in any hotel and down to NR 25 in good-standard bedrooms. It is arguedthat unless a systemis audible, guests will thinkthat it is inoperable. Atmosphere connections andchiller plant shouldbe remoteto hotelbedrooms, or wellscreenedand attenuated.Time clockson, say,kitchen extracts could help byproviding a cut-offtime so plantis not noisyin the early hours. Plumbing noise, particularly 'water hammer', should be avoided by a 'head' to water pipework (307720mmUS practice) or a balloon-typereliefvalve. Housing A BRE Report, Building Regulations and Health[17], mentions a 1980 survey where 18% of residents of new

Table 2.9

Recommended noise ratingsfor health care

facilities Facilities

Quiet wards, overnight stay rooms, chapel,

NR 25—30

resuscitation

New major hospital developments have considerable impact on the local community and the services centre Children'swards, treatment and recovery with its standby diesels, boilers and chillers needs particrooms, staff rest rooms, staffbases, offices ular attention.Attenuation in the ventilation systemsis by theatres, circulation, utility rooms, absorptive material protected by plastic membrane and Operating rooms, day pharmacy, reception areas perforated sheet to avoid the risk of fibrous particles release. Sound-absorbing ceilings (cleanable) and cush- Kitchens, laundry, changing rooms, OT ioned vinyl floor finishes will contribute some noise exercise areas, X-ray process areas, clean control within wards. rooms Hotels Utilityrooms, stores, cleaners' rooms Hotels vary in their standards, most new-built projects being 2- or 4-star. To serve guests, they will usuallybe near dBA levels approximate to NR + 6.

35 40 45

50

H

Acoustics in the Buift Environment

70

houses said they were 'seriously bothered by neighbour noise'. The new Noise Act [22] intended to address this. Understandably, statutory controls centre on providing reasonable conditions in people'shomes. Detailed advice is given in CIRIA Report 127 [18]. The Building Regulations Part E (June 1992 being the last majorupdate of the 1985 version) [2] extend insulation requirements to the conversion of houses into flats and increase significantly the surface mass of concrete in party floors. They determine issues like partywalls and the surface mass of walls that can be taken through party floors (in flats). The minimum sound insulation for party walls is 52 dB (DflTW). The corresponding figure for party floors is 51 dB, and for impact noises the maximum value is 62 dB Lr, Some sample Approved Document Constructions are illustrated in Figures 2.30 and 2.31.

Mean performance

dB D.,

50

o o"o

.

:

p

Mean performance dB

54

tl

4

I

6 Plastered

brickwork

>415 kg/rn2

53

liii! II Ill100

7

0

Plastered

lightweight blockwork >250 kg/m2'

52

Plastered dense

blockwork >415kg/rn2

0

100

200 mm

1. Solid common bricks,frogs 2. 3.

fullyfilled Cavity at least 50 mm wide Wall ties spaced at 900 mm

horizontally; 450 mm vertically 4. Wall plaster, 13 mm

1. 18 mm T&G Floor boarding or 22 mm flooring grade chipboard on 50 x 50 mm battens 2. 13 mm/36 kg/rn3mineralfibre quilt resilient layer 3. 75 mm reinforced concrete screed 4. Cored precast concrete units, at least220 kg/m2* 5. In-situ concreteon permanent forrnwork 6. Plastered soffit

5. Lightweight blockwork, 100 mm 6. Dense blockwork, 100 mm 7. Plaster or plasterboard dry lining on dabs, 13 mm

*amended to 300 kg/rn2 in June 1992 Building Regulations (original specification can still be used with a step or stagger)

Figure 2.30 Selected cavity masonry separatingwalls. (Source: ApprovedDocument ofBuildingRegulations [2]; [18]

200 mm

amended

to 300 kg/rn2

in June 1992 BuildingRegulations

Figure 2.31 Selectedfloatingfloor constructkms. (Source: ApprovedDocument ofBuildingRegulations [2]; [18]

A frequent difficulty is maintaining impact isolation between flats where tiled floor kitchens or bathrooms are installed. There have been recent developments in thin isolating screeds. In considering intrusive noise, environmental health officers will bear in mind recommended maxima for steady intrusive noises (BRE Digest 226 [19]/BS 8233 [16]) Of LAeq,T30—4OdB for bedrooms and 40—50dB in living rooms. Forproposedresidential developments, landwhere the existing or predicted LAeq,T within 15 years is 65 dB should be avoided or sound insulation measures should be provided. PPG 24 [20] introduces NEC (Noise ExposureCategories) for assessingnew housing against existing noise climates. Near airports, planningpermission will be refused for a location subject to 72dBLAeq daytime or 66 dBLAeq night-time (see Chapter 1). Developments adjacent to railway tracks will not only experience high airborne noise but also within 30m may experience ground vibration effects, depending on ground strata. The necessity for special foundation design should be avoided ifpossible.A control value for road traffic noise is 68dB (LAo,l8h)/65dB (LAeq,18h). For industrial noise BS 4142 [21] provides guidelines on determining the acceptabilityofbackgroundexternalnoise in an area.The

Design acoustics

Noise Act [22] deals with noisy neighbours but has no direct design guidance. Industrialbuildings The main issues are noise break-out (particularly for 24-h operating buildings like printingworks, bakeries and flour mills) and good conditions for workers within. The planningauthority may be expected to set a limiting value at the boundaryof the industrial premises, particularly if housing is involved. Noise break-out may occur via the body of the building, if airborne noise levels are high inside and the building is constructed of lightweight cladding. Break-out will also occur via atmosphere processes and ventilation plant connections, for example flues, smoke andprocess extracts, and via goods doorways (particularly roller shutters) and personnel doors. The traffic flow to industrial buildings may itselfbe a noise source problem, for example vehicles parked outside a dairy-produce factory with refrigerator plant

running continuously.

Ancillary sources like signal klaxons, public address

sound leakage or externalPA,and occasional soundfrom

tests of emergency procedures — standby generators, smoke shutters, valve releases — can add to the process and ventilation sources as regards noise break-out. Within industrial premises, the protection ofemployees is afforded by legislation, in particularthe 'Noise at Work Regulations' of the Health and Safety Executive. The effectofthe updatingof this statuteon iJanuary 1990was that three times as many employees became involved. Failure to comply can mean prosecution or even closure for an employer. There is a general duty to reduce risk to employees' hearing, on employers and designers, by reducingexposure to the lowest level reasonably practicable. In known noisy places of work, noise assessments should be made by a Competent Person, and records of assessmentskept until new ones are made. Ear protection zones are designated areas where noise levels will trigger the 'Second Action Level' as defined by the regulations. The unit which applies is the Daily Personal Noise Exposure Levelwhich relates the potentialfor damage to hearing to both level and duration. 1

1T,,

LEPd=lOlo_J

7

'A(t)l

7

= duration of exposure, = 8h, PA(t) = instantaneoussound pressure(Pa) varying with time, P0 = 20 X 10_6Pa. The trade-off has an additional 3 dBA on noise level offset by a halving of duration, 85 dBA LEP d is the First Action Leveland90dBALEP d is the Second Action Level. where

established at definedfrequencies. In setting noise hazard limits the following should be considered: 1. continuous noise sources (to avoid hearing loss), 2. impulsive noise sources (to avoid temporarythreshold

shift), 3. perception of danger warnings, signals (fire alarms, machinery start-up), 4. adequacy of speech communication. For only modest local control (up to 9—1OdBA reduction) a noisy process, for example band resaw machines, can be screenedoff using flexible loaded PVC hung fullheight, of around 5 kg/m2 surface density lined with 25-mm polyurethane. Solid panelling of 13-mm fibreboard with 25-mm bagged rock fibre lining instead can lower the level at operatorposition around by 12 dBA. A modular metal panel system can achieve a 25dBA reduction even with small openings for conveyorsto pass through, whilst full enclosure test cells can obtain a 30 dBAreduction. Modular GRG equivalents are not quite as effective,with a reduction potentialof 20 dBA. Applications are illustrated in the HMSO/Health and Safety Executive publication, 100 Practical Applications of Noise Reduction Methods[231. Another useful reference is SRL's Noise Control in Industry[24]. Often noise in industrial premises is a mixture of high constantnoise (engines, compressors and conveyors)and high maximum noise events (hammering, grinding and stamping). Pneumatic power processes can have intense high-frequency noise components. Localized activity in a large industrial interior forms noise 'hot spots'. If noisy processes are spread out, general treatments will help because workers will each experience noise as a mix of direct sound from other nearby activity and reverberant sound, as well as near-fieldnoise from theirown efforts. If, on the other hand, direct sound from very noisyprocesses nearby dominate, the reduction of the reverberant component ofnoise will be of littlebenefit. Onlyboth a noise survey and an understanding of activitiescan throw light on this. A room treatment of ceiling absorbers can be ofbenefit as follows: sound decay away from industrial noise sources will be greater, perhaps becoming —5dB/doubling of distance rather than —3 dB/doublingof distance; reverberant levels will be lower and there will be a slight reduction of continuous noise, for example from extract fans, due to the added room absorption; reflected sound will be reduced; the 'ringing' character of sound impacts will be lessened. An 'applied' treatment like hung absorbers can be efficient (Figure 2.18) but a built-in inclusion of absorption is cost-effectively dual purpose.The roofsoffit can be rendered absorptive rather than reflective by using a perforated profiled metal deck rather than a plain profiled metal deck, or a lining treatment that is inherentlyabsorptive. The roof offers greater scope than walls because in a large factory, wallsurfaces will be ofrelatively less surface area and perimeters may be remote to

•

dt

Claims ofindustrial deafness hinge on causation, showing loss of hearing on the balance of probability is due to noise at the place of work. The provision of protection and regard for levels and duration plus a plaintiff's exposure to noise prior to employment by the defendant may show that there has not been a Breach of Duty. Contributory Negligence by the plaintiffmay occur if he has not worn ear protection when it was offered or has chosen to ignore directiveson durationofnoise exposure. The standard method for testing hearing is Pure Tone Audiometry, where the employee's hearing threshold is

71

• • •

Acoustics

72

in the Built Environment

working areas. One problem with perforated soffit roof decks is the tendency for a vapour barrier directly behind the perforations to some degree blank off the higher frequency absorption of the quilt behind the vapour barrier. This can be reducedby placing the vapourbarrier as an interlayer between absorption and thermal quilt layers. Lecture and

conference rooms

Lecture rooms

Lecture rooms, purpose-built for 50 up to 500 persons, are a feature of many education and business centres. Up-todate techniques have revolutionized forms of presentation: video conferencing, simultaneous translation, back projection, video recording (for traininguse) and CCTV, BARCO projection, satellite TV links, and computergenerated images.

1.

2.

Thelecture theatre,unlikesaythe council chamber, has set locations for speakerand listener, so finishes can be tailored to flatter the speaker. The front two-thirds of the ceiling should be sound reflective rather than absorptive, the rear absorbing; better still, reflecting ceiling panels can be optimally tilted to give strong early reflections via the ceiling, reinforcing the direct sound. Goodsightlines are essential for adequate sound reception: a dais at the front and tiered seating rows enable this. Reflectingsurfaces at the speaker endcan be 'hard' but best modelled to avoid local cross reflections and resultant flutter echoes which will be off-putting to the speakerand will lessen speech intelligibilityfor the audience. The rear of the lecture room should be sound-absorbing to damp long sound path reflections from the back (Figure 2.32). In considering whether overhead reflecting surfaces usefully reinforce the direct sound, one can consider a

Front panel height determined by projection requirement Panel angled to reflect sound

into body of seating

Section

Sound-absorptivefinishes to rear part of ceiling, rear wall and most of side walls 5.

Sound-reflectivesurfacesto front wall and overhead

0

6.

Projectionroom

7.

Sound lobby

5m

panels

Figure 2.32 Lecture room: Sound-reflectingceiling panels — sections

Half plan (202-seat room) 0

5m

Design acoustics

limiting ellipse within which surfaces can reflect back without echo, but outside of which surfaces should be either absorptive or reflect incident sound so it remains outside the ellipse. A discrete second image of sound is discerned if the reflected sound energy arrives more than 40 ms after the direct sound, i.e. if the distance travelled approaches or exceeds 14m. The notional limiting ellipse is thereforedefined byAB +AC< 14 BC+ 14 where Cis the source point, B the receiver location, andA the surface of reflection. In a space with good room acoustics for speech (RT 0.5—0.75s) the following guide applies: up to 15m relaxed listening

73

reflecting ceilings but edge absorption strips and absorptive wall linings to at least half the wall surfaces (Figure 2.33). PSA and CIBSE recommendations suggest for intrusive/ventilation noise criteria, NR 25 for 'large' conference rooms (>50 persons), NR 30 for rooms holdingmore than 20 persons, and NR35 for the smallest rooms. Soundlobbies shouldbe plannedinto both larger lecture rooms and conference rooms.

Librariesand museums Library activity varies from busy popular fiction and cassette loan areas to quiet reference areas, so the subdivision of the facility by bookstacks and exhibition screening can allow this. Sound-absorbingcarpet,acoustic 15—20m good intelligibility ceilings and soft furnishings can help keep reverberant 21—25m satisfactory soundlevelslow. Ventilation noise shouldbe controlled to 30m limit of acceptability NR 30, intrusive noise from traffic to 45dB (LAeq,TL Museums should be lively centres of activity and Reading lip movements helps intelligibility,which is of assistance up to 15m. When the distance between the 'interactive'/participatory exhibits may have to compete speaker and farthest listener exceeds 10—15m, a speech noisilywith repetitive video presentations. Careful zoning, reinforcementsystem may be considered. sound absorption materials, and good-qualitydirectional sound systems can help. 'Theme tours' are a new Video conferencing derivative. The close arrangementof different 'sets' in a Video conferencing is a newdevelopment entailing voice- tour can allow the effects to be spoiled if noise from one activated cameras and microphone systems to connect area is distracting and intelligible in other areas. specially-adaptedmeetingrooms. Ideally the rooms could be designed to talks studio standards butmore frequently Musicpracticerooms standardconference rooms are adapted. The wall behind The standardoffacilitiesvaries widelybetween the rooms the seated participants should be fully treated with provided in state school music departments — little absorptive facing. Intrusive outside and ventilation noise different to normal classrooms— and isolated,controlled sources should be kept within NR 25. environmentsprovided for professional, and trainee professional, musicians.The smallestpractice rooms hold rooms Conference only two (instructorand soloist); slightly largerones take Conference rooms vary from meeting rooms to large a small group. Large rehearsal spaces can hold sections of auditoria where massed delegates can attend a conven- the orchestra. Surfaceswithin can usefully be sparse (RTs tion. Ideally, office conference roomsshould have sound- typically 1 s at500 Hz for practice rooms, 1.5s for rehearsal rooms), and non-parallel: offsetting alternate walls in a row of rooms by 7° or more is adequate to prevent distracting cross reflections. Low-frequencyabsorbers may be useful to balance reverberation characteristics, and velour curtains can allow some user-choice of playing conditions. Ventilation and steady intrusive noise should be controlled to within NR25 and in all but the quietest settings, rooms should be fully mechanically ventilated. Adequate cross-talk attenuationis essential. The critical issue is the isolation afforded to the rooms. School rooms tend to be a lower specification both because ofcosts andthe desire of teachers to know pupils are practising in individual rooms. Single acoustic doors rather than using sound lobbies may have to suffice. Figure 2.34 shows the commissioned results for a school, The isolation from separated wall leaves is not fully Reflected ceiling realized because of the flanking effects of roof and floor plan continuity. The more costly but effective isolating ceiling and floor shown in Figures 2.35—2.37 show a worthwhile gain in performance, again by carewith acoustic doorsin 1. Sound reflectivecentral ceiling to 'carry' soundlobbies. Even with this degreeofseparation, music speech across the conferencetable 2. Sound absorptive edges to ceiling practice will be discernedin the adjacentpractice room. 3. Sound absorptivewall panelling/piriboard Care in workmanship and supervision is needed, as to at least 50% of wall surfaces contractors find it hard to resist tying structures together 4. Carpetfloor finish for stability during building. An alternative approach, comparable with studio techFigure 2.33 Reflectingand absorbingsurfaces in a small nical facilities, is to use modulardry-construction 'boxes' meetingroom

• • • •

74

Acoustics

in the Built Environment

Wall: plastered 140-mm dense solid blockwork/50-mm, cavity no ties) with mineral wool quilt inlay/140-mm block. 2. Roof:slates on battens, sarking, counter-battens, 12-mm ply, roof Joists void, 13-mm plasterboard, 20-mm timber boarding. 3. Floor: 22-mm chipboardon isolationgrade polystyrene, 125-mConcrete slab. 1.

m a) 1) a)

a) > a)

-J

C

0

riD

125

im

0

Teaching room LIP to 30

I

0

I

250

500

1000

2000

4000

Octave Band Centre Frequency (Hi) sound level difference between: 1 music practice rooms 2 practice room and corridor

I

5m

Figure 2.34 Music practice rooms: !vlanchesterHigh Schoolfor Girls

Isolated masonry construction to walls (although link at foundation and roof). Everyother wall offset 7 2. Sound lobby, doors not opposite in corridor 3. Sealed windows 1.

Design acoustics

75

Subfloor: rc slab Floating floor: 100-mm rc slab on neoprene bearings/ 50-mm air space 3. double ceiling: metal lath + plaster 4. floor above: 200-mm rc slab 5. wall: plastered 110-mm brick leaves, 50-mm quilt, 150-mm cavity (total 540 kg/m2) 6. Wallhead mastic seal 1. 2.

111111

0

I

im

erected within

a building

shell. These may well be as

expensive for the same acoustic performance, but have the advantage of fast installation on site and a relocation ability. Offices

V

Complaints from office workers arise from intrusive outside noise, high noise levels within offices, and poor insulation between cellular offices. BS 8233 recommends LAeq,T values of 40—45 dB for private offices and office conference rooms, and 45—50 dB for open-plan offices. Above a general level of 57cIBA, occupants have to raise their voices to offsetthe background noise,which further raises internal levels.

0)

U C

0) 0)

C 0)

> -J

VC 3 0

(I,

Outside noise levels

63

125

250

500

1000

2000 4000

rd OctaveBand CentreFrequency

(Hz)

sound level difference between music practice rooms

Figure 2.35 Music practice rooms:Royal Academy ofMusic, London. (Courtesy

ofBAP)

Outside noise levels can influence the whole form of an office complex: natural ventilation for a 15-m-deep template or naturalventilation plus ventilated core for an 18-m-deep template allows in transportation or industrial noise, but deep-plan sealed fully mechanically-ventilated office buildings offer a more controlled environment; 4/12/6 glazing is usually adequate, but better glazing combinations (6/20/10 or even double windows) may be required in exceptional circumstances. Atria

Au-ia form the central features of many large office or mixed development/leisure complexes,wherethe working spaces are clustered around a glazed central area which

76

Acoustics in the Built Environment

•

2 N

N

3 N

1.

2. 3.

flmr Fr 0

—7

Floors: 50-mm screed on 25-mm polystyrene on 200-mm rc slab Ceiling: plasterboard on joists Walls: 115-mm lightweight block work leaves, 115-mm cavities, 180-mm central structural wall of dense blocks

im

a controlled internal area with some of the characterof an externalspace. Glazing panels act as low frequency absorbers but are otherwise strongly sound reflective. Combined with hard floor finishes and wall claddings,aclattery,reverberantcharacterwill result unless a proportion, say 25%, of the wall surface is clad in absorptive panelling. Internal modelling serves to diffuse the sound and features like trees, banners, umbrellas, kiosksand other furniture all serve to soak up sound and reduce reverberant sound pressure level. Water features canprovide usefulmasking sound (70dBAatclose range). There is little information on atrium acoustics.Apaper by de Ruiter[25] compares shopping centre, office and hospital examples. In the UK, Gaughan of the Institute of provides

80

a) C-)

C

-/

a) a)

/N

—

0 a)

>

a) -J C

0

(I)

20 63

125

250

500

1000

2000

4000

rd Octave Band Frequency (Hz) sound level difference between music practice rooms

Figure 2.36 Music practice rooms: Birmingham School of Music. (Courtesy

ofBAP)

Environmental Engineering, South Bank Polytechnic,has taken extensive measurements in London atria at the Broadgate Centre (two, each 20m X 11 m X 18m) and the SedgewickCentre (35m X 20m X 15m). Broadgate'smetal, marble and glass finished interior court, four floors high, has reverberation times of 3s at 125 Hz increasing to 9s at 500 Hz. The average absorption coefficient is only 0.05. Sedgewick'sseven-floors heightby contrast has amean a of 0.2 and diffuse, almost Sabine, characterof RT 3s at 125 Hz, 500Hz and 1 kHz.Both centres haveambientnoise levels around NC 50 due to ventilation plant and continuous escalators operation. Three-dimensional sound propagation contours show greatly varying and uneven decay rates of sound from source position to position, due to multiple andcomplex reflection patterns.

Design acoustics

225 350 8

7

77

225!

9

9 T

6 5

2

Brass

5

.3

3

Percussion

4

I 0

Basementslab 225-mm concrete 225-mm brickwork 100-mm r.c. slab on Neoprene mounts (jack-up type)

1. 2. 3. 4.

liii

I

im

120

(upper frequencies not measurable on site)

110

100 a) U C a) a)

fly'

0 a) > a,

-J -o C

11LI / ---

7C-

0

C,)

60-

/ /

--

—

5. 6. 7. 8. 9.

Acoustic wall absorber 25-mm plaster on e.m.l. Flexibleair-tight seal Ground floor slab Services void

Internal noise leveLt Internal noise levels can be kept reasonable by including a sound-absorbing ceiling, carpet and screen-basedworkstation arrangement.Reverberation times are not relevant in open-plan officesas the perimeters are remote.Modern office equipment like laser printers and computer keyboards are much quieter than electric typewriters, e.g. laser printers are typically 64 dBA at 1 m compared to 83dBA for mechanical printers. It may be tempting to consider the use of a sound conditioningsystem. This consists of concealed loudspeakers emitting masking white noise. Care is required as the working sound level for efficient use is narrow: too noisy and the sound is objectionable, or at least draws undue attention to the sources; too quiet and the system is ineffective. Privacy Privacy between work places

is only in the order of

17—20dBA between open-plan screen-based work-stations

50

125 100

200 160

315 250

500 400

630

1250 800 1000

rd Octave BandCentre Frequency (Hz) sound level difference between music practice rooms

Figure 2.37 Music practice rooms: CentralLondon Music College. (Courtesy ofBAP)

at 12m2/work-station, and this may be compared with speech privacy needs as set out in Tables 2.3 and 2.4. These reflect the subjective reactions of office workers, recordedin Table 2.10. Screens can be tested for sound absorption (BS 3638) [261 — a NRC of 0.6 to 0.8 being

desirable — and speech privacy noise isolation class (NIC).

There is a hierarchy of privacy in offices as shown in Diagram 2.6. Surveys have indicated that the thought interruptiondueto office noise can amountto significant work 'downtime' for employees, and good privacy arrangements in open-plan officescan increase productiv-

78

Acoustics in the Built Environment

Table 2.10 Relationship ofbackground noise and annoyance

12

in offices

Staff in an adjacent work-stationannoyed normal speech (%)

l

Activity+ ventilationnoise (dBA)

35 40 45 47

65 40 25

55

4

10

8 C

0

16

Co

6

C C

Co Co

0

4

2

0 0

2

4 6 gap width (mm)

8

10

effectof small gap above an office partition on Sound insulation Figure 2.38 Effrct ofsmall gap above an officepartition on sound insulation

—

— a)

U

a)

C)I C

0

CI

>-) Ccc) .2 .E

.I

oE -J

ity by between 3 and 10%. In cellular offices, proprietary 50-mm-thickmetal-skinned panels with mineralwool core (mass C)

2.4

C)

C) U,

E

I-

C C -C C C C

C

C CO

C)

-o

1.2

S0) C)

C)

>

C)

to

0.8 0.6

0.4 0.2

.2

250

125 (b)

I

I

I

500

1000

2000

4000

+2

10

20

intelligibility 03

a4

es

06

and (b) AGS: Adaptable reverberationby electroacoustics. (Source:Shuttlesound) Figure 2.41(a)

1 2 5 Communication distance )m)

Figure 2.42 Effect ofbackground noise on speech

Frequency (Hz)

oACS1

.5

shell, and ability to balance early andlate sound as well as increasing lateral sound. There may be some overlap with

the house sound system. Such systemsare in a fast stateof development andcare loudspeakers around the hall transmit the modified in commissioning is required so that any artificial acoussignals to supplement the natural sound decay in the tics are not unrealistically 'special effect' and hence auditorium. The systemclaims to 'reshape' ahall as well as unconvincing to professional musicians. For good speech intelligibility, the seating should be just increase reverberation, giving early reflections to an orchestra to make up for the absence of an orchestral grouped as closely as possible to the stage and good

DesigN acoustics

viewlines and reasonable rake provided. Ventilation should be low noise, i.e. less than NR25.

83

References

Opera houses have specific needs, combiningspeech

1. BS 5821: 1984 Methods for rating the sound insulation in buildings and of building elements, British Standards Institution, Milton Keynes 2. Building Regulations 1991 Part E — Sound, amended

Tradingrooms The acoustic environment on trading floors is often regardedas horrific. Wheninterviewedin a survey, traders stated a preference for abalanceof some degreeoftrader privacy and the ability to overhear messages across the room,but this has provedelusive. Whatfirms want is good audibility within a working group, and acceptable use of telephone andintercoms, The whole room is expected to have some 'buzz' to generate excitement. Trading floors ambientlevels can be +10 to +15 dBAabove office interior levels, which causes a poor signal-to-noiseratio so occu-

3. BS 648: 1964 Schedule ofweights ofbuilding materials, British Standards Institution, Milton Keynes 4. BS 2750: Part 9: 1987 Method for laboratorymeasurement ofroom-to-room airborne sound insulation of a suspended ceiling with a plenum above it, British Standards Institution, Milton Keynes 5. BPB/British Gypsum Ltd White Book, September

and music performance. These are well descibed in Barron's book [9], and a good case study publication is the record of Glyndebourne's development [36].

pants shout into their phones and make the din worse; traderwork-stationsare more tightlyspaced, 5 m2/person rather than the 12 m2/person ofopen-plan offices.In the same survey, floor vibration (e.g. from footfall vibration) had not been thought to adversely affect computer screens, even though dealing rooms tend to be plannedin

long-span, column-free structures. The aim should be to create good communication in local groups but diffuse and damp longer sound paths across the room which contribute to the build-up of reverberant noise (Figure 2.42). In reasonable conditions, speech communication could be assumed to embrace 12 to 20 colleagues, across about5 m; this is a slight contrast to the Mohave Desert where experiments earlier this century shows a maximum speech propagation distance of 42 m. Communication beyond the working group is best done by intercom— new headset designs claim to be much more efficient at cuttingout intrusive noise, by improved microphone technology. Thetall exchange rooms ofthe past and double height/ mezzanine rooms in some newtradingfloors provide few surfaces providing useful local reflections for talk between close colleagues. The typical flat low ceiling of acoustic tiles is not a good answer: the surface is more sound reflectiveatglancing angles ofincidence, not less. Abetter ceiling design is modelled ceiling planes, coffers, or suspendedbaffles with absorption on vertical surfaces to absorb long sound paths, and patches of reflection over groups to boost local audibility. The high heat loads make for significant ventilation load andhence high ductvelocities:NR40 or even NR45 is likely to be acceptable. The USA practice is to stack screens and local storage on flat tables which look untidy butallowfast change. The UK 'upright piano' desks as racking to monitors give better local enclosure but limits viewing to other dealers. The ideal is a compromise between local aural field and longer distance awareness of proceedings. A strong determinant on future design will be how quickly voiceactivated computer terminals come in (at present these are being used in small numbers). Perhaps deals will eschew telephone handsets, wear headsets and microphones,andrely on clearer mimic displaysystems; dealing rooms may come to resemble airport control rooms and become quieter and more ordered.

1992

1995

6. Gade, A. C. AcousticalSurvey ofElevenEuropean Concert Halls, Report 44, Technical University of Denmark, 1989

7. Talaske, R. H. (ed.) Halls for Music Performance: 1962—1982, AcousticalSociety ofAmerica, NewYork, 1982

8. Beranek, L. L. Concertand Opera Halls:How they Sound, American Institute of Physics, September 1996 9. Barron, M. Auditorium Acoustics and Architectural Design, E & F Spon, 1993 10. Ando, Y. and Noson, D. (eds) Music and Concert Hall Acoustics —

11.

12. 13. 14. 15. 16. 17.

Conference

Proceedingsfrom MCHA 1995,

Academic Press, 1997 Bickerdyke,J. and Gregory, A. Code of Practice: An Evaluation of Hearing Damage Risk to Attenders at Discotheques, Departmentof the Environment, DGR/ 481/99, London, 1980 Noise at Work Regulations, Health and SafetyExecutive Guidance, 1990 AcousticsinEducationalBuildings, Building Bulletin 51, HMSO, London, 1966/new draft 1995 Guidelinesfor Environmental Design and Fuel Conservation in Edcuational Buildings, DES Design Note 17, HMSO, London, 1981/new draft 1995 LightingandAcousticCriteriaforthe VisuallyHandicapped and HearingImpaired in Schools, DES Design Note 25, HMSO, London, 1987 BS 8233: 1987 Code of practice for sound insulation and noise reduction for buildings, British Standards Institution, Milton Keynes Miller, John, BuildingRegulations and Health, Building Research Establishment Report, 1986, London Sound Controlfor Homes, Report no. 127, CIRIA, 1993

18. 19. Thermal, Visual, and Acoustic Requirementsin Buildings, BRE Digest 226, HMSO, London, 1979 20. Planning and Policy Guide (PPG) 24 Planning and Noise,

1994

Department of the Environment, September

of rating industrial noise affecting mixed residential and industrial areas, British Standards Institution, Milton Keynes (under

21. BS 4142: 1990 Method

22.

review)

The Noise Act, September 1996 (into force April

1997) 23. 100 Practical Applications of Noise Reduction Methods, HMSO/HSE, London, 1987 24. Noise Control in Industry 3rd edn, Sound Research Laboratories, Spon, London, 1991

84

25.

Acoustics

in die Built Environment

de Ruiter, E. Ph. J., Atria in Shopping Centres,

Office

Buildings and HospitaLs, IOA proceedings, 10(8), 1988 26. BS 3638: 1987 Method for measurement of sound

absorption in a reverberantroom, British Standards Institution, Milton Keynes 27. Specification for Studio Centres, Engineering Code of practicefor Independent Local Radio- Issue 2, Independent Broadcasting Authority, London, February 1988 28. Acoustical Properties of Control Rooms and Listening Rooms far the Assessment of Broadcast Programmes,

ReportR22, European Broadcasting Union, London,

1985 29. Borwick,J. SoundRecordingPractice,OxfordUniversity Press, Oxford, 1987

30. Rose, K. Guide to Acoustic Practice, 2nd edn, BBC Engineering, Oxford, 1990 31. Talaske, R. H. (ed.) Theatres for Drama Performance, Acoustical Societyof America, London, 1985 32. Forsyth, M. Auditoria: Designing for the Perfanning Arts, American Institute of Physics, NewYork, 1987 33. Appleton, I. Buildings for the Performing Arts: A Design and Derelapment Guide, Butterworth Architecture, 1996 34. Mulryne, R. andShewring,M. MakingSpacefor Theatre: British Architecture and Theatre Since 1958, Mulryne & Shewring Ltd, 1995 35. Steele, J. Theatre Builders: A CollaborativeArt, Academy Editions, September1996 36. Binney, M. and Runciman, R. Glyndebourne— Building a Vision, Thames and Hudson, 1994

Chapter 3 Services noise and vibration

Settingdesign objectives

Peter Sacre and Duncan Templeton

condenser units may be in a louvre-screened compound open to atmosphere. Local plant. Decentralized ventilation systems can have advantagesoflower cost (no long duct runs) and flexibility (zoned units).However,plantnoise sources are taken out of the sound-insulating plant room and into userspacesandso careis neededin their siting. There are already a number of guides on the noise control of building services. For a number of years, the noise control products trade has concentrated on noise from fans in central ventilation or air-conditioning plant transmitted through air distribution ductwork. Specialist acoustic suppliers via technical sales personnel can select and supply the appropriatepackage ductwork and associated attenuators. As a result, there should be relatively few noise problems in buildings due to inadequate fan noise silencing through ductwork. However, many problems exist due to poor ductwork layout or high velocities causing regeneratednoise. For the typical commercial or public sector building, the following potential noise sources and transmission paths may need to be considered:

The areasofdesign forwhich noise criteria need to be set

are as follows:

• Central plant.

'Plant rooms' are often split (airhandling units in roof-level housing; boilers and pumps in ground level or basement rooms). Chiller

•

Background

The control ofnoise from mechanical and electrical plant can be a vital area of design, as failure to meet criteria is more readily perceived than, say, room acoustics criteria. The designerneeds to be aware ofthe need to limitnoise inside and outside the building: in occupied internal areas, where noise can be irritating or distracting, or can affect working

•

• efficiency; in industrial premises, where processes rather than rooms are serviced; • occupied in the areas immediately surroundingthe building,

which may be used for circulation or leisure, where excessive noise can be intrusive and may present an environmentally unsatisfactory character; beyond the site boundary — excessive noise from plant may cause nuisance, leadingto complaints and legal proceedings, especiallyin residential areas. The importance of noise depends mainly on two factors:

•

• the typeofbuilding whetherits use dependson low levels, and • noise the location particularly the proximity of other —

—

noise-sensitiveareas beyond the boundary. Noise control should be an integral part of the design procedure. Too often noise aspects are introducedinto a design too late, and in an ad hoc way. The role of any advice from an acoustics consultant or silencing specialist should be proactive rather than reactive. The cost is many times greater for a retrofit compared to the original inclusion of adequate noise control measures. The key participants who can influence services noise are:

• the client: including noise criteria in the brief, from site to room data sheets • the layout architect: provision of adequate structure, sen• • • • •

sible location and area allocation of plant rooms, planningin distribution routes the mechanical engineer: total design of HVAC systems, setting criteria the electrical engineer: design of substations, emergency generators, lifts the mechanical and electrical engineeringsubcontractors: detailed selections of components and installation the acoustics consultant or engineer: design advice from briefing to commissioning the specialist supplier of noise control hardware: providing data and goods to match initial selections.

• Internal noise Central

air-handling plant Fan noise to ducts Airflow-generated noise in ductwork, at duct fittings or dampers Noise break-out through duct walls Noise generated at grilles and diffusers — Local air-conditioningplant and room units Fan-coil units Volume-controlterminalunits Heat pumps Local extract fans Fan convectors Warm air curtains — Piped services Pump noise or flow noise radiated from pipework or from building surfaces to which pipework is fixed Water hammer Flow noise from drains, particularly WC, soil pipes and rainwater pipes from roofs — Electrical equipment Emergency generators Uninterruptiblepower supplies, generator sets Transformers Thyristor speed controllers and light dimmers, fluorescent lamp ballasts — Airborne or structurebornenoise transfer through plant room envelope to adjacentareas — Other sources Kitchenequipment Laundryequipment Workshop machines —

86

Acoustics in the Built Environment

Waste compactors Lifts Escalators Documenttransfer systems Computers (integral fans)

• External noise

Atmosphere terminations

—

Flues Louvres opening into plant rooms Louvres ducted to fan inlets or exhausts Boiler flues Generatorflues — External equipment Airhandling plant Roof extract fans Cooling towers Air-cooled condensers Packaged chiller plant Design approach

The building services are most frequently designed by a Mechanical Services Consulting Engineer, with the buildingenvelopeandsupport structurebeingtheresponsibility of other consultants. Other specialists may be involved; silencing products designers, acoustics and energy consultants for example. The role of such specialists may be limited to provide 'designintent' sketches, draft specifications, and guidance, which 'main profession' consultants will incorporate in contract documentation for construction purposes. It is important to realize that structure, layout, furnishings, fittings and furniture will have a fundamentaleffect on the noise from building services installations. The design output typically consists of drawings and specifications which form the basis of a legal agreement between client and contractors. It is essential that the design intent and the necessary design details for noise control are clearly and exhaustively covered in the drawings and specifications. Many noise problems in finished buildings are due to inadequateinformation, or to poor communication with the contractors, rather than to a fundamentally deficient design. Information at the out-to-tender stage varies from line diagram schematics, with minimal sizing of ducts and no identification of silencers, to full documentation: ductwork to scale, duct velocities, sized attenuators and schedules. There is a danger that an engineerwill take a specific specialistsupplier's quotation very literallyand in its entirety, including octave band values for particular silencers. These are in fact specific to the fan being used and cannot be checked at the commissioning stage, so a schedule of sizes, types and location will suffice, room criteria being the commissioning target. Buildings designed by integrated practices, or by 'design and build' contractors, should present fewer problems caused by inadequate flow of information between professions. However, the need remains for a formalized procedurefor noise control design. The noise input requiredat the various stages ofdesign are identified in Table 3.1. In some cases, noise from services maybe a critical issuewhich fundamentally affects the layout or structure of the building, as well as the approach to building services. The design team can

Table 3.1 Services noise advice timing Activity/decisian

Noise input

Feasibility, preliminary design:

Provisional design criteria Identify critical spaces Suitable plant type Suitable plant locations External noise survey Provisional external criteria Adequate structure

Detailed design:

Develop design criteria Planningconditions Internal plant selection Externalplantselection Louvre locations Duct sizing, routing Duct attenuatorselection Terminal units Grille/diffuser selection Vibration isolation Plant room construction Check drawings/notes Design criteria stated Plant maximum noise

Site location Site use Space layout Building structure Location of central plant Method of servicing rooms Location of external plant Size plant, confirm location Size ductwork Duct runs, damper positions Plant-room structures Select terminals, room units

Drawings and specification

levels

Attenuatorschedules

Equipment arder

Vibration isolation schedules Specificationsfor noise control equipment Works noise tests Check equipmentagainst specification Approve changes and %%Taivers

Installation

Site checks

Commissioning

Measure noise levels Highlight/diagnose/solve problems

address each services noise issue as it arises, from 'is the

plant room big enough andfar enough away?' to 'is there enough space in the ceiling void we've assumed?'. Noise control is a basic requirementbecause higher standards (lower-value criteria) mean lower duct velocities, and hence largerducts,for the sameduty. Roomcriteria are a big clue to the type of system suitable in a ventilation system, for example NR 25 implies two-stage attenuation andfully-ducted systemsto air-handlingunits in a separate plant room, NR 35 or 40 implies single-stageattenuation, relativelyhigh velocities,and common use of ceiling voids as plenums or for volume-control terminals.

87

Services noise and vibration

effect ofnarrow-band tonalnoise and discriminate is a general need to control noise and set criteria low-frequencynoise. Usually NR curves rather thanagainst Noise both within and external to buildings. There are several Criteria (NC) are usedin the UK for considering services levels of noise requirements within buildings. Examples noise. Generally, NR and NC values can be interare: changeable but there are variations: technical areas where particularly high standards of at low frequencies, NR values exceed the equivalent noise control are required. These may be small NC values; (music practice rooms, audiometry suites, continuity at high frequencies, NCvalues exceed the equivalent voice-over studios) or large (concert halls, conNRvalues; ference rooms); NR values run between 31.5Hz and 8kHz, NC between 63 Hz and 8kHz althoughin practice 63 Hz working areas where noise from services can be the dominant noise source, for example offices, laboto 4kHz is typically used in design checks for ratories, and hospital wards. Noise control shouldnot either; NR values are on true curves determinedby formula; only be adequate to not intrude on conversations or a spectrum can be stated as any NR, e.g. NR 31. NC telephone calls, but for ventilation to be unobtrusive; curves are defined in steps of 5, e.g. NC 30, NC 35. industrial buildings and the interiors of large plant The limitations of this can be avoided by stating the rooms where high noise levels can be produced and excess over the lower value, e.g. NC 30 + 1. occupants may need to be protected. An example is Air-conditioning noise can also be checked by Room in newspaper printing centres (Figure 3.1). Only in Criteria these refuges looking onto the presses, with sound American(RC) curves as recommended by ASHRAE (the Society of Heating, Refrigerating and Air reducedto below 65 dBA, cancontrollers take offear defenders and make telephonecalls or conversation. Conditioning Engineers), but neither RC or PNC (PreNoise Criterion) curves are in general use in the In very noisyenvironments an additional difficultyis ferred UK 3.2 and 3.3 and Figures 5.6—5.9). (Tables the audibility of alarms and announcements. Attitudes vary on the relative values ofventilation noise The acoustic consultant and silencing specialist are levels and background noise levels, although values are essentialin the first category but also have a lot to offer in generally based on CIBSE banding. If ventilation noise the design of the other categories. levels are setvery low, it will be difficult to commission the To determine acceptable criteria, the first point of reference should be the project client who, on a large scheme, may have his own specialistadvisers,for example Table 3.2 Design criteriaa hospital resident engineers or property managers and maintenance engineers. Ideally, a brief would be enlarged Environment NC or NR by room data sheets including environmental standards as baseline data.Where existing premises are to be altered or 10 extended, surveys of existing noise levels, noise climate Radio drama andairborne and impact separation, may be useful. talks, continuity studios, live television The room activity and use combined with the existing Radio studios 15 ambientnoise from other internal and external sources will suggest a criterion for services noise. This criterion is Recording studios, audiometric rooms, often established by reference to a Noise Rating (NR) concert halls, opera halls 20 curve. This allows a check against the sound character cathedrals and large churches, which is limited by the use ofa single-figuremeasurement, Theatres, commercial television studios, large i.e. dBA. Single-figureunits fail to pick up the annoying conference and lecture theatres, music practice rooms, hotel bedrooms, Design critiria

There

• •

• • • •

•

courtrooms

Senior management offices, small conference andlecture rooms, multipurpose venues, libraries Cellular offices,multiplex cinemas, restaurants

Circulation in public buildings, open-plan offices,ice rinks, swimming pools, cafeterias Shops, bars, WCs, supermarkets Warehouses, industrial premises, laundries, kitchens Figure 3.1 Noise havens: printing hail

25

30

35

40 45 50

aSeealsoTable 2.9 with regard to health care facilities criteria.

88

Acoustics in the Built Environment

Table 3.3

Criteria

values (in dBf OBCF (Hz) 31.5

63

125

250

500

1k

2k

NR NC PNC RC

66

47 47 43 —

35 36

26 29

19 22

15

12

9

7

17

12

11

35 35

28 30

21 25

8

8

20

14 10 15

10

—

NR NC

69

51 51

39

—

PNC RC

59

46

39

40

20 22 20 25

20

14 17 13 15

13 16 13

—

24 26 26 30

17 19 15

—

31 33 32 35

NR NC

72

55 54 49

35 37 37 40

29

25

31 31 35

27 25 30

22 24

20 22

—

44 44 43 45

20 25

18 20

18 21 18 —

59 57 52 55

48 48 46 50

40 41 41 45

34 35 35 40

30 31 30 35

27 29 25 30

25 28 23 25

23 27

52 52 50 55

45 45 45

35 36 35 40

32 34 30 35

30 33 28 30

28 32 28

50

39 40 40 45

57 56 54 60

49

44

50 50 55

45 45

40 41

37 39

40

36

33 37 33

50

45

40

35 38 33 35

61 60 58 65

54 54 54 60

49 49 50 55

45

42

46 45 50

44

40 43

38 42 38

Criterion value

Criterion

15

20

25

30

35

40

58

—

PNC RC

— 60 —

NR

76

NC

—

PNC

61

RC

—

NR NC

79

PNC

62

RC

—

63 60 55 60

NR NC

83

67

— 64 —

64

86

71

— 67 —

67 63

PNC RC 45

—

NR NC PNC RC

—

59 65

70

40

15

41

45

4k

38 40

8k

—

23

—

—

—

—

"ForNR,NC and PNCcurves, see Chapter 5, Figures 5.6—5.9.

system because ambientnoise will tend to dominate, and the client will not be gettingvalue for money in an oversilenced installation. If the levels are too high, the system itself is obtrusive. Around or slightlybelow (0 to —5dBA) averaged activitynoise is usually found to be acceptable; ventilation noise can have a useful masking effectin roomto-room speech privacy (as indicated in Table 2.3 in Chapter 2). In order not to add noise from different services sources, 'local' ventilation noise from room supply and extract grilles should exceed by at least5 dBA noise break-out, or re-radiated noise, from primary plant. In considering a criterion, the 'steady state' ventilation noise to be introduced has to be considered relative to both background noise from traffic noise break-in and equipment noise like computer fans, andvarying ambient noise from occupants' activity.

madeto Guide toAcousticPractice [1], EBUReportNo. R22, AcousticalProperties of Control Roomsand Listening Roomsfor the Assessment of Broadcast Programmes[21, and the IBA's Specificationfor Studio Centres[31.

Externalnoise Environmental noise control is generally covered in Chapter 1, under Industrial Noise. Emission limits from fixed plant andprocesses may be written in as a planning condition, or should be established early in the design process to avoid the local environmental health officer agreeing with complainants thatthe plantnoise is a public nuisance to neighbouring properties and is therefore actionable under statutes. Different local authorities take different attitudes. Some, not wanting prevailing neighbourhood noise levels to 'creep' up due to the addition to newexisting sound, will ask for existing levels not to be raised. This is very Broadcasting authorities The BBC, IBA and EBU (European BroadcastingUnion) onerous, as to reliably enable this, the new sources will all have recommended criteria. Reference should be have to be 10dBA less than existing levels. It is normally

Services noise and vibration

acceptable to control daytime noise emission at the nearestnoise-sensitivepropertiesto not exceedprevailing levels, and by this means limit any possible increase to 3dBA maximum. Night-time noise control is likely to be stricter, say —5 dBA on existing levels. There is then the task of the consultantas client's representative, to agree with the local authority an interpretationof'existing noise climate'. This is the generator of many sound levels surveys. Assessments

89

Structurebornenoise

A by-product of vibration is structureborne noise and althoughthe vibration levels in abuilding maybe low and satisfactory,

the noise levels radiatedfrom a structuredue

to vibration may exceed required ambient noise levels. This is normally only a problemwhere low noise levels are requiredin areas suchas auditoria, conference roomsand bedrooms, and only where these areas do not have windowsthat would allow low frequency break-in noise to

of noise complaints will often be basedon mask the structureborne noise. Although reduction of BS 4142, Method of rating industrial noise affecting these audio frequencies relating to structurebornenoise mixed residential and industrial areas [4], seen as an can be achieved by isolating the building, reductions of importantguidebylocal authorities. Problems canarise in 5—10dB only are likely to result. The use of resilient pads derelict areas, previously bustling with industrial or to isolate the building will not significantly reduce low commercial activity but now awaiting redevelopment, frequency vibration levels. because the reference existing background noise levels are 'temporarily' particularly low. There is dependenceon the operating hours of plant. Office ventilation systemsmay cut off in the evening but computers andrefrigeration plant need to stayon for the full 24-h cycle. Hotel public rooms and kitchens have systems which can go on into the early hours, to the possible consternation of overnight guests. Ice rinks and swimming pools have large-duty plant which has to keep the ice frozen, or water conditioned, continuously. The designer needs to be sure of the cut-off times before designing all plant to daytime background noise levels. Intermittent noise may be the subject of negotiation with the local authority, fora relaxation ofnoise control (say +5 to +10dBA or NR on night-time criterion values) of standby generators, knowing that they will be 'run up' regularly but for relatively short periods during the daytime. Any continuous operation will be exceptional, for example power failure, and an increase in the nighttime noise level will be temporarily acceptable ifthe units have to be run continuously. Noise break-out for other emergency plant,for example fire pumps, powered smoke extract systems, would normally be exempt. Vibration Perceptionofvibration

People can be quite sensitive to vibration, particularly where the source of the vibration cannot be seen. Satisfactory levels of vibration for people in different building types (Figure 1.12) and in the three different axes, i.e. vertical and the two horizontal directions, are given in BS 6472, Guide to evaluation ofhuman exposureto vibration in buildings (1Hzto 80Hz) [5]. The velocitycurves from BS 6472 are given in Figure 3.2. However, these 'satisfactory' levels will be greaterthan those which can be perceived or felt. Vibration effects in buildings are typically in the 2—50 Hz frequency range. In designing a building, it is necessary not only to take accountofpeople, where different standards could occur, e.g. industrial environment compared to office, but also the possibleeffectofvibration on sensitiveequipment. This could be projectors in multiplex cinemas (projectors are effectively optical instruments) or more exacting still, microchip manufacturing processesor delicate balances in laboratories. Offices may not seem sensitive areas, but structurallyadequatelong-spanfloorstructures can exhibit substantial movement even due to people walking across themandthe effectcanbevery disturbing to staff.

Buildingdamage Consideration also needs to be given to the protection of a building or other structurein order to prevent damage from such activities as piling or press operation.Guidance on vibration levels for different building types to avoid damage is given in BS 7385: Evaluation and measurementfor vibration in buildings [6]. However,it is worth noting that the levels of perceptionby people and the levels that are considered to be satisfactory by BS 6472 are well below those vibration levels that could cause damage to buildings. Furtherdetails relatingto groundbornevibration are given in Chapter 1. Sources

There are various potentialsources ofvibration:

• industrial activitiessuch as presses or generators, • building servicesplant either associated with general

air-conditioning/ventilation systems or installations such as lifts, footfall due to the movement of people. Natural or resonantfrequency is discussedin Chapter 5. Floors, walls and indeed entire buildings have their own resonant frequency characteristic. This resonant frequencycan be excitedby a single blow such as footfall, as described earlier for long-span floors. Mechanical plant as used in building services, in addition to having its own natural frequency due to its mounted condition, also has forcingfrequencies which are a function of its own operating conditions, e.g. running speed. Vibration can occur in any combination of six modes: vertical, longitudinal, horizontal/traverse (linear motions), rolling, pitching and yawing (rotational motions). Services designers' concern will be primarily with the vertical mode. The effect of vibration transmission into a building structure from mechanical plant will be determined by the relationship between the forcing and natural frequencies. This is illustrated in Figure 5.10 for a single one-degree-of-freedom system. When the forcing and natural frequencies are close then the vibration from the plant will be easily transmitted to the supporting structure, therefore to controlvibration transmission the ratio of the frequencies must be changed. The natural frequency of the supportedplant is dependent not only on its own mountingbut also on the supporting structure.

•

90

Acoustics

in the Built Environment

1.

E 0)

E C

0 a) a)

0 0

0.01

0.00W

(a)

Frequency Hz

Frequency Hz

(b)

Figure 3.2 Building vibration x- and y-axis curvesfor (a) peak accelerationand (b) peak velocity. Extractsfrom BS 6472 are reproducedwith the permission ofBSI. Complete copies ofthe standard can be obtained ly post from BSI Publications, Linford Wood, Milton Keynes, MK14 6LE

Long-span lightweight construction can inherently be easily 'driven' and Steffens's Structural Vibration and Damage [7] quotes other BRE guidance to stay clear of low (approaching 5Hz) natural frequency characteristics. Higher values of 10Hz or more should be sought for floor structures. Having obtained a rigid structure from the structural engineer, it is necessary to introduce resilience into the support ofthe plant usingvibration isolators. The correct selection ofvibration isolator has to take into accountthe naturalfrequency ofthe supportingstructure. Disappointingperformances will be obtained for isolators selected to achieve 95% isolation if the machine is mounted on the mid span of lightweight steelwork. Other parameters associated with vibration isolation include static deflection which is a function of natural frequency and, since it is a more readily identifiable unit, is very useful. Damping will also need to be considered in assessing vibration isolation, since it will reduce the anticipated isolation performanceof a system.

Design considerations Types

ofequipment

During the design phase, it will be necessary to consider a wide range ofpotentialnoise and vibration sources. Some of the major items are discussed below. General advice is given but itwill be necessaryto obtainmeasured data from manufacturers and followdetailed prediction routines. Fans

Noise in fans is generatedby: blade action airstream effects at fan surfaces resonantfan casing vibration fan drive/motordrive and vibration For the usual constantfan speed, the least noise occurs when the fan is on or around its maximum efficiency. 'Stall' speed or overspeed should be avoided. Derating pulley changes resulting from 'over-engineered' systems may not improve the noise character.

• • • •

Servicesnoise and vibration

91

0 a)

m a) > a) a)

0 a 0 C

0

C),

63

125

250

500

1000

2000

4000

8000

Octaveband centrefrequency (Hz) AxiaI fans (100 dB L)

Figure 3.3

Centrifugal fans (98 dB L)

Typicalfan noisefrequencyspectra

Typically, turbulent flow is random and causes broadband noise across the audible frequency range. There are pure tones at the blade rotationfrequency and its higher harmonics, as an overlay to this broadband noise. Fan noise data of concern are the octave band sound power levels ofnoise via the intake, exhaust terminations, and as radiated via the fan casing and external motor. Reference bodieswhich may be quoted in a performance specification include CIBSE [8] in the UK and ASHRAE in the US. Pending selection or as a cross check of manufacturers' claims, an estimate can be made from

has a useful initial guide (Table3.4).Axial and centrifugal fans produce similar sound power, with axial fans having higher high-frequencyvalues (Figures 3.4 and 3.5). Air-handling plant Air-handling plant of modern design consists of the fan unit itself (which may be centrifugal or axial), flexible connections, casing and chassis, filter, coils, mixing boxes, and possiblyintegralattenuators and dampers.

empirical formulae andtypical spectra (Figure 3.3) based Cooling tower/condeizser units on the duty of the fan. Noise arises from the fan, fan motor assembly, and water An empirical formula for sound power level at inlet or turbulencedown to sumps. Regenerated noise may occur outlet is: via water circulation pipes. An indicative sound power level is given by: I=40+10logV+2Ologh L.N = 11.5 + 10 log P where Vis delivered volume (m3/s), his fan static pressure (N/rn2). SRL's book, Noise Control in BuildingServices[9], where P is the total rated fan power output (in watts). Table 3.4 Typicalfan noise spectra OBCF' (Hz)

Equipment

63

125

250

500

1k

2k

4k

8k

Fans (up to 75mm static pressure) 25 hp 40 hp

95

94 97

91

84 87

79 82

74 77

69 72

64 67

lOOhp 250 hp Fans (150mm static pressure or over) 50 hp

lOOhp 250hp

98 101

104 107 111

113

94

100 103

90 93

85

100

87

88

80 83

85 78

80 83

106 110 112

103 107 109

96 99 102

91

86

94 97

89 92

81 84 87

76 79 82

92

Acoustics

in the Built Environment Directivity factors will be important as condensers are typically screened in a compound rather than fully enclosed. A typical spectrumis shown in Figure 3.6. Refrigeration units

Fridge plant compressors may be annoying by virtue of intermittency of operation.Typical spectra are shown in

Airflow

Figure 3.7. Boilers

Sound pressure levels are fairly similar for different types

offuel and representative octave band SPLs are given in Figure 3.8. The principal noise sources are the fuel burner units and combustion air fans. Noise will also be discharged up the flues and is predominantly of a low frequency character. Prediction formulae are given in CIBSE/ASHRAEbut caution is necessary in view of the large number of variables (flue height, directivity, crosssectional area, linings, etc.) inherent in empirical formulae.

Figure 3.4 Axialfan

Generators

In many public buildings, emergency powerfor light and safety procedures is provided by battery sets. Some

Airflow

11

industrial premises, hospitals, broadcasting centres, and officeswith vital constantpower needsforcomputers, etc., will include emergency power generators, frequently in the form of diesel engines. Noise comes from: Airflow

'1

• engine itself, • the • exhaust, intake, • air cooling fan, • ventilation openings t&engine enclosure.

It is misleading to measure engine sets when run-up in routine tests because full load cannot be applied. Noise control measures shouldbe applied as a kit:

• enclosure, with controlled ventilation supply and

Figure 3.5 Centrifugal fan

extract openings by attenuators,

-o

> a

0 0

250

500

1000

2000

4000

8000

Octaveband centre frequency,Hz

Figure 3.6

a

Typicalfrequencyspectrum ofair-cooled condensersat distance of3m based on 300kW model

Services noise and vibration

100

---

__________--_____--

93

_______

a, > a, a,

J

a,

C

0

U)

Octaveband centrefrequency. Hz

Figure 3.7

a

Typicalfrequencyspectrumofreciprocatingchillersat distance of 1 m based on 600kW model

95 -

90a, > 4' 4,

85-

a,

C

0

C',

250

500

1000

2000

4000

8000

Octaveband centre frequency, Hz

Figure 3.8 Typical boilerroom noise levels

•• exhaust • provide substantial structures around the plant silencing, possiblytwo-stage, inlet silencing, acoustic doorsets where necessary, • vibration 10-mm static deflection rubber • including ensure any service penetrationsof the structure do notdowngrade its sound insulation performance, efficiently isolate the plant to control vibration

isolation,

engine mounts are usually adequate for basement floor slab placement.

• transmission, • provide any noise control necessary to reduce noise external to the building, • fans or air-handling units will typically require

Gas turbines Gas turbines are industrial engines used for power attenuationon both the intake and exhaustsides of generation,pumpingand compression. The soundpower level will depend on the engine rating but at mid the fan, frequencies can be around 120dB. As with standby give a limiting sound power level for all majoritems of plant. generators, noise emanates from the turbine itself, the exhaust, and noise from the discharge of turbulent hot gases. Treatmentcan be by silencers, speciallydesigned to withstand the hot gases, and some form of acoustic Valves enclosure. Valves are frequently the source of peak noise events at Noise design concerns for the above items of plant are industrial plant complexes. The valves may be either addressed in the following summary: for emergency only or to control flow in a system. By their nature, valves produce noise as a by-product of plan location of plant, or plant rooms, away from high pressure air, or other gas, relief. The sound critical areas, power level of a valve may be in the order of 150dB.

•

•

Acoustics in the Built Environment

94

'Streamlined' valves help to a degree but the type and location can improve the situation: reducing jet size can shift the sound energy to higher frequencies which are more easily attenuated by screening and distance. 'Blow off attenuators' are available for mounting on 'pepper pot' arrays of small outlets. Such installations are the province of specialist process engineering designers.

Lfls

Lifts can present an annoying intermittentnoise source in blocks offlats, hospitals, or even office buildings. Low-rise hydraulic lifts have fewer moving mechanical parts but are best specified with submersible pump and motor, casings lined with sound deadeningmaterial, and suitable vibration isolation not only ofthe pump and motorbut also of the pipework. The lift motor should be mounted on vibration isolators and the doors should be selected for quiet operation. High-speed lifts should not give wind whistle and air pressure rattles at doors panels. The intermittency of motor and doors operation can draw attention to the noise, in an otherwise quiet environment. Diverter sheaves can cause vibration in older models; good maintenance will help lifts to keep running smoothly and quietly. For both fire and acoustic separation, any builder'swork holes in lift shaft walls should be made good. Modern commercial buildings may have lift shafts in dry construction (multi-layer plasterboard for example), rather than masonry; the isolation of lift noise can be as effective with care and attention to the sealing of the multiboard edges atjunctions. A large property managing group has the following standardcriteria as a performance specification in office

Escalators

Escalators can give rise to noise levels around 50—55 dBA locally,with strongdependenceon treadspeed (+12 dBA/ doubling of speed); squeal and clanks can arise from treads and handrailsin worn examples. A checklist of noise concerns is as follows:

• use sound-insulating casing to drive, gearing,

• • •

and

chains, apply dampingto resonant panels, ensure maintenanceto treads and handrail, review electrical noise sources: armature design, mountings.

Vibration can occur from the escalator operation and also from personnel movements on and off it. Vibration on the escalator steps should be less than 1 mm/s rms vertical vibration velocity (above 5 Hz). Operationshould be imperceptible on adjacentfloor slabsbeyond 2 m from the end combs. Lighting

This is only likelyto be ofconcernin low-noise (NR 25 or less) rooms. Fluorescent lights have noisy ballasts (chokes), so should be avoided in such areas, unless remote starterchokes are plannedin. Low-voltage lighting with local transformers can produce noise. While an individual lightfittingmay not seem a noisyitem, an array of 50 in a small lecture room may allow distinct tones, buzzes or harmonics to build up. There may also be noise from light fittings incorporating return air slots. Sound power levels are 35—40 dB at 0.04m3/s through a fitting. Such fittings alsoallow a route for room-to-room noise, so attenuation may have to be incorporated iflightfittings are within 1.5 m either side of partitions or if a high performance separation is schemes: required. High-level mercury discharge lighting in sports halls Door noise 1.5 m from floor and1 m inside door shall may produce around NR 30 which will be acceptable for notexceed 65dB precision SLM set on 'fast' sports use but may need reviewingif other events are held response. there. Noise levels at maximum car velocity, measured as for lifts of above, should not exceed 55dB for lifts of Ventilation velocities 0.5—2 rn/s or 60 dB systems velocities 2—7rn/s. Lift noise within lift lobbies measured as above to be Fan noise within 55dB Noise is basically due to the fan, and air flow causing regenerated noise at dampers, control branches and A checklist of lift noise design concerns is as follows: bends, and terminals. CIBSE B12 gives a step-wise procedure for calculating the noise control requirements for plan lifts next to non-critical areas, e.g. stairs, fan noise and a design example is shown in Table 3.5. Guidance is also given in ESDU 82002 (Reduction of stores; a substantial with structural sound in ventilation and similar air distribution sysshaft, preferably provide breaks to the main building structure; tems) [10],ESDU 81043 (Soundin low-velocityventilation use large-diameter resilientwheels to counterweights ducts) [11] and ESDU 82003 (Example to illustrate the and close tolerances at use ofdata items on noise from ducted ventilation andair rails; • isolate motor room,andguide form attenuatinglined tube conditioning systems) [1211. Initial design is assisted by the availability of micropenetrationsfor suspension cables; allow controlled ventilation openings to shaft to computingroutines where parameters are fed in for the avoid 'air pump' effects of pressure build-up during calculation of resulting room noise levels. Softwarepacklift movements; ages are included in most mechanical engineers' CAD use low-noise high-qualitydoorsand signal bells. routines.

• • • • • •

• •

(L),

Services noise and vibration

95

Table 3.5 Example ofdetermination offan noise through ductworksystem at 125Hzfrequency Stage 1.

Level,

Determine fan sound power level,

dB at 125Hzfrequency

L 90

2. Determine ductwork system losses Duct attenuation

lOm of 700 X 500 ignore remainder

2 X vaned

Bend attenuation

—4

bends

0

[volumeat grille

Branchattenuation

10 log I

L

End reflection at termination

—11

fan volume

grille area = 0.2m2

—5

3. Resultant sound power level at each grille, Lwg 4. Determine room losses Reverberant correction to obtain Lprev = +10 log n — 10 log V+ 10 log RT+ 14 dB n = no. ofgrilles =4 V = volume of office = 360m3 RT= reverberation time in office = 0.7 s 5.

Reverberant sound level, rev Direct correction to obtain Lp dir = —20 log = distance to grille D = directivityfactor

r

6. Direct soundlevel,

r

— 11

70

—7

63

+ D dB = 1.5 m

—10

L dir

60

7. Determine total sound level in room total = rev + dir

L

L

8. Design criterion

65

NR 35

52

9 Attenuation required

13

To less noise-sensitiveareas 1.5 m3/s

Vaned bends 700 x 500 duct

Branch loss

Fan 2.1

r

——

Fan room —_---

grille 0.45 x hOrn

L

L

12m

Nearest most noise-sensitivearea: office with design criterion of NR 35 Schematicof ductwork system

0.45

m

96

Acoustics

Table 3.6

in the Built Environment

Typicalattenuatorinsertion loss (in dB,f OBGF (Hz)

Length (mm)

63

125

250

500

1k

2k

4k

8k

500

5

7

10

15

23

17

13

1000

8

11

19

31

48

37

28

11 21

1500

10

16

27

45

50

50

39

31

"The attenuatorperformancedependsnot only on its length but also on the ratio of airway-to-splitter width (refer to Figure 3.12). These insertion loss figures are for an attenuatorunit with an approximate ratio of 1:2.5 (airway:splitter).

The main sound components in assessing the need to control fan noise are:

• fan sound power entering the system, •

•

• •

• dampers, grilles, • branchesinducingturbulence. Cross-talk can be designed outbylayout orallowedforby attenuation or adjustment of grille size. Typical

attenuation at branches and straight runs of lining, ductwork, insertionlosses at attenuators, diffuser and end reflection effects, room effect.

Attenuation

Attenuation along ducted systemscan be achieved by:

• length of duct run, • lining ofinternal surfaces, a practice favoured in the attenuators. ducts is more effective

USAover Linings for small ducts and higher duct velocities, bends, plenum chambers. Attenuators, or silencers, are purpose-made sections of lined ductwork with splitters to incorporatealargesurface area ofabsorption along the attenuatorlength. It is usual for the attenuatorto have greatercross-sectionalarea than the ductitis in, to avoid undue pressure drop.Thelocation is importantandthe performance is assessedby: insertion loss (typical insertionlosses for particular lengthsof attenuatorare shown in Table 3.6),

• •

• • pressureloss, • airflow noise.

In low velocity, low static pressure systems, the fan may be the only significant noise source, i.e. there are no great regeneration problems. High pressure, high velocity systemsneed more detailed calculation.

are set out in Table 3.8. The method of assessingcross-talkrequirements is given in Diagram 3.1. In office buildings, ceiling voidsor underfloorvoids are often used as supply or extract plenums, with air passage viagrilles andpossiblylightfittings.Suchsystemsin offices are more economic, saving on ductwork, but limit the scopeforattenuationand canlead to room-to-room crosstalk problems. requirements

Duct noise break-out To reduce fan noise break-out from ductwork, ducts can be lagged by a barrier mat (quiltwith lead foil interlayer), Keene's Cement (not now favoured) or studwork panel Table 3.7 Maximum recommended ductvelocities In-ductair velocity (mis)

N-R or NC design requirement 20 25 30 35 40

Main

Branch

Final run-outs

4.5 5.0 6.5 7.5 9.0

3.5 4.5 5.5 6.0 7.0

2.0 2.5 3.25 4.0 5.0

Regeneratednoise

The basic layout of the ductwork and the air velocity within it influences noise levels most. The optimal placement of attenuators and other in-line duct items is critical. Recommended maximum duct velocities are as shown in Table 3.7, for low velocity systems. The flow rate of air in a duct can be checked by a calibrated inlet device or by static suction in the early part of the system. Regeneratedduct noise can be created by:

•• bends transition pieces, (turningvanes alleviate noise),

Table 3.8

Cross-talk attenuation

Requirement in receiver room

NR 40 NR35 NR3O

NR25

Attenuator length (mm)

Noise reduction at 500 Hz (dB)

750

25 30 35 40

1000 1250 1500

Servicesnoiseand vibration

97

Determine Lw at grille in source room taking into account source room losses

A = area of grille

INo

Diagram 3.1 Method ofdetermining cross-talk casing. A layer of 12kg/rn2 lead on mineral wool will increase the sound reduction of the ductwork by 5 dB/ octave.

Duct shape influences in-duct noise and duct noise break-out characteristics. Circular ducts are more rigid andofminimum perimeterfora particularcross-sectional area thus reducingnoise transmitted into rooms or ceiling void. Hence circular ductwork is often preferred in exposed system installations within spaces. Rectangular ducts have less rigid wallsandthe flat metal is more easily excited, and although it may provide low-frequencyinduct attenuation, it allows more noise break-out at low within frequencies. This can lead to 'drumming' heard duct the room through which the passes. Builder's work ducts can be used for low velocity systems in, for example, auditoria. These are long plenum chambers formed in airtight masonry or plasterboard (Figure 3.9). The advantages are:

• lower cost than equivalent very large-scale metal • ducts, easier installation, use of • efficient

building's space.

The disadvantagesare:

• mixed responsibilities of main contractor and ductwork supplier, in avoiding pressure drop-off from a take • difficultiesend to one at the other, off at one • good workmanship is required to ensure an airtight chamber.

The builder'swork details at ductwork penetrationsof wall need careful attenuation (Figure 3.10). Riser ducts are a feature of the distribution from plant rooms in multi-storey buildings. They can be either masonry or dry construction. Access doors to high velocity riser ductwork should be acousticallyrated. Transfergrillesare frequently usedto save ductwork runs in ventilating adjoining small rooms, but negate acoustic separation. They may be used only for acoustically noncritical partitions or doors. Large public spaces

Large public spacespresent a conflict between large-scale air distribution and noise generation, particularly in large noise-sensitive volumes like auditoria. High occupancy

98

Acoustics in the Built Environment

In office buildings, ceiling voids or underfloor voids may be used as supply or extract plenums, with air passage via grilles andpossiblylightfittings. Such systems in offices are more economic, saving on ductwork, but limit the scope for attenuation (single-stage only) and lead to room-to-room cross-talk problems. Central and room units

Preference for centralized systems rather than room or sector ventilation units is based on ease of maintenance and separation of plant rooms from served spaces. However, there are now many good package units available and a sensible compromise which may be considered is to have centralized plant providing basic airhandlingto user areas, with an overlayof room units for specific high-load areas. This is often a solution for 'tenant's plant' installed as a fit-out contract to suppleFigure 3.9 Air plenum above recital hall ment the landlord'sserviced shell. Room units can be of different types: air-handling only, by a packaged unit recirculating air demands good ventilation but high ceilings mean long througha chamberwhereit is tempered chilled or 'throws' for ceiling-mounted supply systems against the heated pipework, and then mixed with abyproportion 'natural' convection currents. An alternative claimed to of fresh air make up; save half the cooling load on a recent theatre projectis the • air conditioning by wall-mountedunit, with a fan coil Europeancommonpractice oflow-level, underseatsupply on the room side and a condenserunit outside; and overhead extraction, all at low velocity (Figure fan coil units which recirculate and temper air, with 3.11). control by varying fan speed; Anotherissue in large low-velocity systems is the pointat induction units which by jet action move the air which it becomes more economic to go from complete within the space many times the supply air velocity; metal duct systems (which are the responsibility of the ducted air systems, as a scaled down version of a to a mix of engineeringsubcontractor), ducted systems centralized ventilation system; and 'builder's work' air-sealed plenum chambers for terminalunits, which alter 'mains' supply of ducted supply or extract (Figure 3.9). air locally.

•

• • • •

Services noise and vibration

Each system has a characteristic noise and, unlike centralized plant, the ventilation units are within the user space rather than segregated in a plant room. Fan coil units have a typicalsound power spectrum of around NR 50—55 profile, terminal units around NR 40—45. Some optional extraimprovement can be gained by selection of a quieter standard model, damping casing radiation, fitting attenuators (the back pressure implication needs checking), and acoustic lagging. Manufacturers of fan coil units and also grilles invariablyquote an achieved NRor NC level by their units based on an estimated room loss. This room loss is often 8 dB and assumes only one unit serving it, whereas the actual value could be 3—5dB thus underestimating the asinstalled noise levels situation. Plant rooms

Plant in older buildings was placed on the basis of 'boilers in the basement, tanks on the roof. Modern plant rooms house not only boilers and pumps but also

:1

-2 3

I

I

1. 2. 3.

Lintels over Mineral wool packing to keep cavity clear Dense mineral wool slabs to all sides of duct Mortar pointing between slabs and brickwork reveals Metal flanges bedded in non-setting mastic

air-handling units, lift motors, compressors, and open-toatmosphere chiller plant. Plant-room noise levels are 4. typically in the range NR 70—85 for boiler rooms, NR 60—75 for air-handling plant rooms. Masonry structures 5. — concrete floors, concrete, brick or blockwork walls — are essential, with metal acoustically-rated access doors. An SRI of 50dB (100—3150Hz) is a minimum require- Figure 3.10(a) Builder's work penetrations: duct through ment for walls and floors. Additional airborne attenua- wall tion through the floor can be achieved by the introduc1. Oversize stubmetaltube tion of a floating floor. 2. Preformed dense mineral The roof structuresound insulation will need considerwool 3. Pipe throughwall, not ing in the case of roof-mounted freestanding air-handling units often used on commercial, retail or multiplex mechanically fixed at the wall cinemas projects. 4. Hole filled with mortar Absorptionin plant rooms may reducereverberant sound pressure levels by about 5 dB but it is usually more cost effective to have noise control at source or increase the sound insulation of the plant-room structure. If possible, expensive shrouds to units should be avoided as after initial maintenance there is a tendency to leave enclosure panels loose or detached altogether.

Plantroom structure Once the location of plant or plant rooms is fixed, consideration needs to be given to providing an adequate plant room structure. In addition to determining the appropriatemain construction which is typically masonry, any openings and penetrations by ductwork or pipework

have to be carefully designed. Acousticdoorsets may have to be specified. Metal doorsets are capable of achievinga highersoundinsulation than a timber type. In specif'ingacoustic doorsets, care must be taken in selecting the appropriate performance from manufacturers' data. Figure 3.10(b) Builder's work penetrations: pipe through Ventilationopeningswill normally need to be acoustically wall controlled by attenuatorunits or acoustic louvres. Service penetrations will need to be effectively sealed. or openings into fully enclosed plant rooms — air inletsor Suitable details are given in Figure 3.10. exhausts, and plant room naturalventilation. Externalplant Condensers are often roof mounted and therefore do Noise to the outside can be from plantwhich by its nature not benefit from ground attenuation or natural screenneeds to be open to the atmosphere, screened areas or ings by proximity to walls. Suchunits often have to run at freestanding plant rooms holdinggenerators or chillers, night and so have to be considered relative to low

100

Acoustics

in the Built Environment Advantages Lower cost

•

Disadvantages fights natural convection underseast noise break-in weakness difficult to avoid draughts throw (and hence noise produced) too great for concert halls

• •

•• Overhead supply underseat to extract to plenum

• standard practice in quality •

halls: best system for concert halls and low-noise auditoria high degree of control of airflows

• higher cost • suits fixed seating only

Under seat supply, high level extract

• suitable forflexible seating halls • cluttered ceiling voidwith both (bleacher seating)

supplyand extract duct runs

with lighting bridges • clashing difficult to achieve 2.2 s? — Or is it moderately live, — —

1.5—2.2 s?

Sound systems —

Or is it acousticallyfairly dead, OW

-I-il

CL

OW .r1C Ui-I

4J WI

:1.

L

LO

Q4J U

0

jo

5

0

Difference Between Levels

(MB)

Figure 5.2 Adding noise sources

will be the A-weighted sound level if A-weighted.

L or P is

If the sourceradiates non-uniformly then the equations must be modified to =

— 20

X log10 r— 11 + DI dB

as, for example, when measuring sound intensity directly with an intensity probe. The sound intensity level should always be quotedwith a reference quantity, e.g. 120dB re 10_12 W/m2. Sound pressure level: The sound pressure level, L,, is defined as

or

L

= 10 X log10 P— 20 X log10 r+ 109 + DI dB

L,1

= 20 X log10 (p/p0) dB

where p is the sound pressure and p° is a reference where DI is the directivity index of the source in the pressure which for propagationin air has the value 2 X direction of i

Sound intensity level: The sound intensity level, IL, is defined as L1

= 10 X log10 (I/Is) dB

where I is the acoustic intensity which is defined as the power passing through a unit area perpendicular to the direction of travel of the power. Intensity, therefore, has units of watts per square metre (W/m2). is a reference intensitywhich forpropagation in air is chosen as 10_12 W/m2. In many cases the sound pressure level and the sound intensity level have the same numerical value for a given sound and they can be used synonymously. However, circumstances do exist where this equivalence does not hold andthus itis better if the sound intensity level is used exclusively fordescribing the ratiooftwo sound intensities

I

iO- Pa.

Hence,as 20 X log (2 X 10-/2 X 10) = 0, a sound pressure level ofzero dB is equivalent to a sound pressure

of2 X

i-

Pa.

Also, as 20 X log10 (20/2 X 10-s) = 120, a sound pressure level of 120 dB is equivalent to a sound pressure of20 Pa. The normal range ofhumanhearingthus covers the range 0 to 120dB. When a sound pressure level is given it should always have an associated reference quantity, e.g. 120dB re 2 X iO-5 Pa.

An increase of 3dB in the sound pressure level of a noise is thought to be the smallest change that is subjectively definitely noticeable under normal testing conditions. An increase of 10 dB on average represents a doublingin loudness of the noise. Sound level/noiselevel: Sound level and noise level are often used instead of sound pressure level.

136

Acoustics in the Built Environment

0 113

B

0

A.

C

C

0 .1.1

U CC-

0

C-)

0

0

(U

113

00

00

0 0 (U

113

0 0 0

00 0 (U

Frequency

(Hz)

00 0 113

00 00 1

00 00 (U

Figure 5.3 A—D weightings

instrumentbetween the microphone and the display. The A-weightingattenuateslow and high frequencies relative to 1000Hz. The standardA-weighting curve is shown in Figure 5.3 and detailed in Table 5.2. The A-weightingis where Pis the acoustic power of the source in watts (W), the most frequently-usedweighting network, especiallyfor and P0 is a reference sound power chosen in air to be rating environmental noise. 10-12 W As 10 X log10 (1/10_12) = 120, 1 acoustic watt is B-weighting:The B-weighting is similar to the A-weighting equivalent to a sound power level of 120dB re 10_12 W except that there is less attenuationat low frequencies as = shownin Figure 5.3 andTable 5.2. The B-weightingis little 10 X + dB log10 (P) 120 L. used. Source on a reflective plane:When a source, assumed to radiate uniformly is placed on a reflective plane, e.g. on a concretesurface, the energy radiatedabove the plane is C-weighting: The C-weighting is essentially flat except effectivelydoubled. The source directivity factoris 2 and below 50 Hz andabove 5000Hz as shown in Figure 5.3 and Table 5.2. It is not often used although it has been the directivitv index is 3dB. Hence, suggested that it should be usedto describe low-frequency short-duration events. L.=L—20 X log10 r—8dB Sound power level: The sound power level, LD is defined as = 10 X log10 (P/P0) dB

L

or Constant bandwidth filters: These are filters that have a bandwidth which is constant independent of the band Fora source at thejunction between two reflecting planes, centre frequency. e.g. a door in a wall on a hard ground, DI is 6dB. Digital filters: Digital filters are computer algorithms which filter digital signals in the same way that electrical Weightingnetworks andfrequency bands networks filter analogue signals. A-weighting: Human hearing is not equally sensitiveat all frequencies. In addition, the variation with frequency is a Fast Fourier transform: The Fourier transform is a functionof the sound pressure level. To try and account method for transposing information in the time domain for this variation when measuring sound, electronic to information in the frequency domain. The fast Fourweighting networks are incorporated in the measuring ier transform (FF1) is a computational algorithm which

L = 10 X log10 P— 20 X log10 r+ 112dB

137

Technical information

Table5.2 Specificationofweightingnetworks Frequency

(Hz) 10 12.5 16 20 25 31.5

40 50 63 80 100 125 160 200 250 315

400 500 630 800 1 000 1 250 1 600

2000 2500 3150 4000 5000 6300 8000 10000 12500 16000 20000

Curve A

CurveB

Curve C

(dB)

(dB)

(dB)

—70.4 —63.4 —56.7 —50.5 —44.7 —39.4 —34.6 —30.2 —26.2 —22.5

—38.2 —33.2 —28.5 —24.2 —20.4

—14.3 —11.2

—19.1 —16.1

—13.4 —10.9 —8.6 —6.6 —4.8 —3.2 —1.9 —0.8

0.0

0.6 1.0 1.2 1.3 1.2 1.0 0.5 —0.1 —1.1 —2.5 —4.3 —6.6 —9.3

—17.1 —14.2 —11.6 —9.3 —7.4 —5.6 —4.2 —3.0 —2.0 —1.3 —0.8 —0.5

—8.5 —6.2 —4.4 —3.0 —2.0 —1.3 —0.8 —0.5 —0.3 —0.2 —0.1

-.0.3

0.0 0.0 0.0 0.0 0.0

—0.1

0.0

0.0 0.0 0.0

0.0 0.0 0.0

0.0

-0.2

—0.1 —0.2 —0.3

-.0.4

-.0.5

—0.7 —1.2 —1.9 —2.9 —4.3 —6.1 —8.4 —11.1

—0.8 —1.3 —2.0 —3.0

—0.1

Octave band filter: An octave band filter is an electrical network which allows frequencies within the octaveto pass unattenuatedbut reducesfrequencies outsidethe octave Curve D to an insignificantlevel.Frequenciesjustbeyond the limits (dB) of the band are notalways reducedto a level atwhich they do notcontributeto the band. Theperformanceofa filter —27.6 in these regions will dependmuchon its design. Thereare —25.6 a number of different classes of filter with differing —23.5 attenuation rates at the filter limits. The octave band sound pressure level, L, can be —21.6 —19.6 obtained from the one-third octave level L)1, L2 and —17.6 by summing the levels as incoherent sources, i.e. —15.6 = 10 log [10LP1/1Q + 102110 + 103/10] dB —13.6 —11.6 or by adding the levels two at a time using Figure 5.2. —9.6 Octave band sound pressure level: The sound pressure —7.8 level measured when only frequencies within an octaveare —6.0 passed is known as the octave band sound pressurelevel. —4.4 Analysis of noise into octave bands is frequently used in —3.1 the assessment ofa noise climate.

L

—1.9 —1.0 —0.3

0.0 —0.1 —0.4

0.0 1.9 5.4 8.0 10.0 11.0 10.9

—4.4

10.0 8.5 6.0 3.0

—6.2 —8.5 —11.2

—0.4 —4.4 —8.1

Octave band spectrum:When the sound pressurelevels in adjacentoctaves are plottedagainst the centrefrequencies of the octave bands this is known as an octave band spectrum. It is accepted practice to plot the centre frequencies at equally-spaced intervals, i.e. on a loga-

rithmicscale.

One-third octave band: Two frequencies are said to be one-thirdoctave apart if the frequency of one is 1.26, or more precisely 10015, times the other. There are three one-third octaves in each octave band. The standard centre frequencies and bandwidths of one-third octaves are shown in Table 5.3. The width of a one-thirdoctave band is 23% of the band centre frequency. Environmental noise measures A-weighted sound pressure level: This is the sound pressurelevel measuredusing an A-weightingnetwork to filterthe sound. Thesoundpressure level has units ofdBA

so the soundlevel would be given, for example, as 80dBA or more correctly as 80 dBAre 2 X iO- Pa. The A-weighted sound pressure level is the basic used in most environmental noise assessment at much measure greater speeds. performs the transformation The FF1' will produce a frequency spectrum where the indices and schemes. frequency information is at fixed frequency intervals. Calculation of A-weighted sound pressure level from The frequency spacing depends upon the time intervals octave band sound pressure levels: The A-weighting between the original data samples and the total number attenuation for the centre frequency of each octave is of time domain samples. added arithmetically to the octave band sound pressure Linear-weighting There is no standard linear weighting. level andthe resulting levels are added togetherconsiderIn general it should have a flat unattenuated response ing them to be separate noise sources (see combination of sound from several sources), e.g. between 2Hz and 20 kHz. 125 250 500 1 k 2 k 4 k 8 k O.B.C.F (Hz) Octave band: Two frequencies are said to be an octave O.B. 80 80 80 80 80 80 80 if of one is or more twice, precisely L1, (dB) apart the frequency the of the other. 1003, A-weighting frequency —16.1 —8.6 —3.2 0 +1.2 +1.0 —1.1 (dB) Contiguous octavebandshave centre fre9uencies which The centre O.B. are also related by a factor of two (1003). A-weighted 63.9 71.4 76.8 80 81.2 81 78.9 L,,, (dB) frequencies andbandwidths ofstandard octave bandsare shown in Table 5.3. An octave bandwidth increases as the centre frequency ofthe band increases. Eachbandwidth is 70% of the band centre frequency.

10

A-weighted level = 10 X log (10639 + 10714 + 108 + 10812 + 108.1 + 10789)

A-weightedL.,, = 87dBA

+

138

Acoustics

in the Built Environment

Table 5.3 Octaveandone-third octavecentrefrequenciesand band limitfrequencies

Standardfrequencies (Hz) Octave

Band No.

Preferred centre frequency (Hz)

Third-octave

Band limits

Centre

Centre

22.39 14

25

15

31.5

16

40

17

50

18

63

19

80

20

100

21

125

22

160

23

200

24

250

25

315

26

400

27

500

28

630

29

800

30

1 000

31

1 250

32

1 600

33

2 000

34

2500

35

3 150

36

4000

37

5000

38

6 300

39

8 000

40

10 000

Band limits 22.39

25.12 28.18 31.62

31.62 35.48 39.81

44.67

44.67 50.12

56.23 63.10

63.10 70.79 79.43

89.13

89.13 100.00 112.20 125.89

125.89 141.25

158.49 177.83

177.83 199.53

251.19

251.19

223.87 281.84

316.23

354.81

354.81 398.11

446.68 501.19

501.19

562.34 630.96 707.95

707.95 794.33 1

000.00

891.25 1

000.00

1

258.93

1122.02 1 412.54

1 584.89 1 995.26

1 995.26

1 412.54 1 778.28

2 238.72 2511.89

2 818.38

3 162.28 3981.07

3981.07

5011.87

5 623.41

6 309.57 7 943.28

7 943.28 10 000.00

11 220.18

2 818.38 3 548.13

4 466.84

5 623.41 7 079.46 8 912.51 11 220.18

Technical information

139

Average sound level, L, This is the same as the For example, if a source of noise level 100dB is on for 0.5 h in 8 h its effective 8-h Leq will be equivalent continuous sound level Leq.

= Correctednoise level (CNL):This is the A-weighted sound Leq,81i 100 + 10 log 0.5/8 level which has been modified to take account of pressure = Leq,8h 88dB any distinguishable characteristics of the noise. It is defined in BS 4142. Remember tand Tmusthave the same units, whetherit is If the noise has a noticeable tonal component, e.g. a seconds, hours or days. whine or hiss, is impulsive or in any way is such that it The corrections to obtain the value can be obtained draws attention to itself, then 5 dBA is added to the from the chart shown in FigureLeq 5.4. measured sound level. If one or many distinguishing features exist, 5 dBA is only added once. Percentageon-time Day/night equivalent sound level, DNL (LON): This is a 0.1 0.5 5 10 50 100 rating, based on the equivalent continuous sound level 0 Leqwhich has its origins in the USA. The acoustic energy is averaged over a 24-h period but the noise level during the night-time period (22:00—07:00 hours) is penalized CC by the addition of 10dBA. 0a) 22 00 1 10LA/1O dt C LDN = 10 log [— I 0 [24

J7

r7

+

a)

+

1

'°"° dt

dBA

0

J

J22

where LA is the instantaneous A-weighted sound pressure level. For effectively constant noise levels an estimation of LDN can be made in the same way as the normal Leq 5

estimated (see above). LDN has found widespread acceptance in the USA for environmental noise assessment.

dB

noiselevel forpercentage Figure 5.4 Correctionto measured on-time

Ifthere are a numberofsources the corrections can be T (dB): The applied to each source in turn and then the total Equivalent continuous sound level, Leq i' continuous equivalent sound level, Leq,1' is a notional obtained decibel addition, by e.g. soundlevel. It is the soundlevel which ifmaintainedfor a On time Correction Corrected given length of time would produce the same acoustic Source Level level (dBA) (h) (dBA) as a noise over the same time energy fluctuating period. It is defined mathematically as 1 80 4 —3 77

L

L

Iii p2 (t) dtl1dB r=lOXlogI—l [Ti

j

2 3

85 77

2 8

—6

(10

0

10)

79 77 = 82.5dB

8-hour Leq = 10 log + iO'° + one use Alternatively, may Leq,8h = l0141,'10 x t1 + .. . + 10'-P"° — 10 log T L1 is soundpressurelevel which is on for time t1, etc. So, for the above example, the 8-hour Leq = 10 log (108 X 4 + 1085 X 2 + X 8) — 10 log 8 = 82.5dB.

wherep(t) is the acoustic pressure which varies with time; Tis the total time over which the Leq,TiS calculated; p° is 2 X iO Pa. If p(t) is A-weighted before the Leq,T15 calculated then the Leq.Twill have units of dBA. The above formula is implemented electronicallyin all good sound level meters and it is customary to measure rather than calculate the equivalent continuous sound The individual noises can be all on together, on level. It should be remembered that any value of Leq,r separately,or overlap.Itwill makeno difference to the Leq should be accompanied by the time over which it was level. measured. Leq, T is widely used to measure any environMaximum sound pressure level, This is the maxmental noise which varies considerably with time. imum value of the sound pressure level that occurs during Estimation of the equivalent continuous sound level: It is any given period.Itsvalue will depend upon the frequency possibleto estimate the equivalent continuous sound level weighting and meter time characteristic. The maximum for a source or numberof sources if theyhave effectively slowA-weightedsound level during an aircraft flyover is constantnoise levels over known periods of time. used in the assessment of aircraft noise (see 'perceived Ifa sourceofnoise level, L,, is on for a period of time noise level'). then the Leq value, over a period T where T is greater than or equal to t is Minimumsoundpressurelevel, This is the minimum soundlevel that occurs duringany given period.It is little = used in assessment procedures, comparedto L10. Leq, r L1, + 10 log t/TdB

iO

l.:

140

Acoustics in the Built Environment

Noise andnumber index, NNI: This is an indexwhich was where p(t) is the sound pressure which varies with time used in the UK for rating aircraft noise until 1990. It is over the period T The soundpressureis oftenA-weighted before the SEL is calculated. defined as The sound exposure level is related to continuous NNI = averagepeak perceived noise level + equivalent level by 15 logN-8O = SEL — 10 log T dB 1-Seq. where Nis the number of aircraft having a PNL greater where T is the time in seconds over which the Leq is than 80 PNdB in the specifiedperiod.The average PNL is required. given by If identical SEL values occur in the time 7 the Leq is N given by 1 10 log I— 4q,T = SEL — 10 log T+ 10 log NdB IloL/N I dB If the events are not identical then the 4q equivalent of each event must be found and then the total whereL is the peak value of PNL during the passage of calculated by adding the individual Leq values as decibels the ith aircraft. are added. NNI has been replaced by 'tq, P An approximate relationship between NNI and the 16-h Statistical level, L1: This is the sound pressure level that is A-weighted Leq is exceeded for 1% of the measurement time. It gives an indication of the maximum sound levels that occur. NNI 16-h Leq (dBA) 35 57 Statistical level, L10: This is the sound pressure level that is 45 63 exceeded for 10% of the measurement time. Conse55 69 quently it isindicative ofthe higher levels that occurin the Peak sound pressurelevel: This is the sound pressurelevel measurementperiod. In the UK the A-weightedL10 value is used to measure corresponding to the peak sound pressure that occurs in and assess traffic noise. For fairly noisy traffic anygiven period.Its valuewill dependuponthe frequency weighting and the time characteristics of the measuring Leq + 3dB

r

L

system.

It is often usedto quantif' short durationimpulses, e.g. gunfire, explosions and high level impact noise. To measure the true peak sound pressurelevel of an event, great care must be taken in the selection and use of microphone and measuring system.

Perceived noise level, PNIL: The perceived noise level is a rating for single aircraftflyovers based originally on jury judgements of perceived noisiness, but it is now commonly derived by an extensive calculation procedure. Formost generalpurposes the perceived noise level can be obtained from measurements of the maximum slow A-weighted sound level that occurs during a flyover. PNL = dBA + 13 PNdB.

L_:

SEL=lOXlogf

Jo

p2(t) dtdB 2 Po

L

Sound insulation Sound insulation: Airborne

sound insulation refers to the of a process separating, by physical barrier, a space to be

protected from a space containing a noise source. With noise insulation the sound is effectively prevented from travelling in a specific direction by an impervious barrier. The greater the surface mass of the barrier, the greater the insulation will generally be. Unlike soundabsorption, This is sound insulation does not remove energy from the sound

Single event noise exposure level, SENIELor equivalent to the sound exposure level. In the original definition it was assumed that the sound pressure was A-weighted andthat the integration was over the time that the signal was within 10 dB of the maximum value. Sound exposure level, SF1.. or The sound exposure level is a notional level. It is the sound level that if maintained constant for 1 s contains the same acoustic energy as a varying noise level. It is normally used to quantify short duration noise events such as aircraft flyover, single vehicle bypasses, impact or impulsive noise. It is defined mathematically as

L:

Statistical level, L90: This is the sound pressure level that is exceeded for 90% of the measurement time. Consequently it is indicative of the general ambient noise level in the absence of any higher level short-duration events that occur during the period. The A-weighted value is often used as a measurement of background noise in environmental assessment.

field; it merely redirects it.

Sound reduction index, Sm: The sound reduction index is the measurement generally used to express the insulation propertiesof a partitionin decibels. It is definedas SRI = 10 log10 (1/transmission coefficient) dB

The soundreduction indexis frequency dependentandis

usually measured in octave or one-third octave bands. If the transmission coefficient T = 0.01, i.e. 1% of the incidentsoundenergy is transmitted by the partition, then the sound reduction index is 20dB, while if'r = 0.001 the SRI is 30dB, etc. Hence for 50 dB insulation, which, for example, may represent a reasonable reduction between flats, the incidentintensity must be reduced by a factor of 0.000 01.

Technical infonnatio.i

The octave band soundreductionindex,R is obtained from the one-thirdoctave band indices R1, R2 and R3 as follows (see addition of attenuations, part (b)) R = 10 log 3 — 10 log [10_Riiio + 10o + 10/1oI dB R = 4.77 — 10 log[l0h/10 + 10?/o + l0-''°I dB

R = 4.77 + C

141

Sound level difference between two spaces: The sound

level difference between two spaces separated by a partitiondepends upon the value ofthe sound reduction index, the area of the partition and the acoustic properties of the two spaces. (a)

room-to-room

= L1 — R + 10 loglo (S/A) dB Lp2 Figure 5.1 can be used to find C. This addition assumes equal energy in all three octave (b) inside-to-outside bands. — R+ 10 log10 5—20 loglo r— 17 + L2 = Sound transmission coefficient, T: The sound transmission coefficient is a measure ofthe incidentsound energy DI dB that 'passes through' a wall, partitionor any barrier. The sound doesnot actuallypass through the barrier. Incident (c) outside-to-inside sound energy causes the barrier to vibrate and the = L1—R+10log10(S/A)—K+6dB vibrating barrier then radiates sound into the receiving as The sound transmission coefficient is defined is the soundpressure level on the sourceside (dB), space. is the sound pressure level on the receiver side L2 Intensity incident upon a partition (dB), S is the area of the partition (m2), Intensity transmitted by partition R is the sound reduction index of the partition (dB), Transmission loss A is the absorption in the receiving room (m2), Coincident effect critical frequenc When sound waves DI is the directivity index of the facade, strike a partition, bending waves are excited in it, the r is the distance of the receiver from the partition. velocity of which depends upon the frequency. As the K is a constant, the value of which depends on where, frequency of the bending wave increases, the bending external to the the sound partition, pressure level was wavevelocity increases and at some frequency, known as measured: the critical frequency,it is equal to thevelocityofsoundin air. At this frequency the wavelengthof the bendingwave K = 6 dB if measured very close to the partition, is equal to the wavelength of the sound in air and if the K = 2.5 dB if measurementposition is about 1 m, sound wave impinging on the partition is of the same K = 0 dB if measurement position is far from facade. frequency, resonant excitation can occur and the sound transmission of the panel is increased and the sound Sound transmission class, STC: This is a single figure reduction index decreased. descriptor used for rating the sound transmission of a of the at the critical Matching wavelengths frequency partition obtained by laboratory measurements. The occurs at grazing incidence and little energy is actually measured sound reduction indices in one-third octave transferred to the partition. However, as the frequency bands are comparedwith a set of standard curves and at increases above the critical frequency, matching occurs at each frequency the difference between the measured increasing angles ofincidence and energy transference to valuesand the standardcurve valuesis obtained. The STC the partitionis significantlyincreased. value corresponds to that curve for which the sum of the The reduction in performanceof the panel is known as deficiencies is less than or equal to 32 dB and the the coincidence effect and the performance of the maximum deficiency at any one frequency is less than partitioncan be significantlyreducedat frequencies in the 8dB. The reference curve for an STC value of 52 is regionofthe critical frequency althoughat an octaveorso beyond the critical frequency the panel will again Frequency (Hz) Level (dB) approachits expected performance. 36 125 Field sound transmission class, FSTC: This the STC 160 39 obtained from values of the sound reduction index 42 200 measuredunder field conditions. 250 45 315 48 The transmission of sound transmission: flanking energy 400 51 via paths which bypass a partition is known as flanking 500 52 transmission. 630 53 Noiseisolation class, MC: This is the STC obtainedfrom 800 54 values of the sound level differences measuredbetween 1 000 55 two spaces under laboratory conditions. 1 250 56 1 600 56 Normalizednoise isolation class, NNIC: This is the STC 2000 56 obtained from values of the sound level differences 2500 56 measured between two spacesunderfield conditions. The 56 sound levels in the receiving room are corrected to a 3150 4000 56 standardreverberation time of 0.5s.

142

Acoustics

in the Built Environment

The value of the STC is equal to the dB value of the curve correctedto a standard receiving room reverberation time at 500 Hz. Other standardcurves are obtainedby moving of 0.5 s. Hence this curve up or down in increments of 1 dB. DnT = measured level difference + 10 log T/0.5 dB SRIofcomposite construction: A composite construction T = reverberation time in receiving room. is one havingareas with different sound reduction indices, Structureborne sound: Sound which travels from one e.g. a wall with windows. space to another not through the air but through the For a facade consisting of areas S1, £2 with S fabric ofthe is known as structurebornesound. It sound reduction indices R1, R2 R,1, the value of the is one formbuilding of transmission. Structureborne flanking sound reduction index for the facade is given by sound can travel long distances with little attenuationand be re-radiated, causing problems far from the original + ... + S, S1 + source of noise. R= 10 log10 i x X + 1o-R10 S1 Lb0R1b0 £2 Transmission loss, TL: Transmission loss is an alternative name for the sound reduction index. +. + X Sn Weighted apparent sound reduction index, R: This is similar to R.but is usedifit is thoughtthat the value of The composite sound reduction index may also be was obtained with flankingtransmission. obtained using Figure 5.5, taking two areas at a time. sound level difference, D: The weightedlevel Small areas of very low insulation can drastically Weighted difference is obtainedfrom level differences, measured in reduce the overall performance of a facade, e.g. an one-third octave bands, in exactly the same way as the opening of area 0.1 m2 and SRI 0dB in a facade of area airborne sound insulation index rating, R, is obtained. 25 m2 and SRI 50 dB reduces the overall SRI value to 50 — 26 = 24dB. Weighted sound reduction index, R: This is a weighted single figure descriptor of the sound insulation performStandardized sound level difference, DflT: The standar- ance of a partition measured under laboratory condidized sound level difference is used to assess airborne tions. The sound reduction index in each of the onesound insulation between rooms in buildings. As the third octave bands from 100Hz to 3150Hz is compared sound level difference across a partitionwill depend upon with a standard set of curves. The value of I? for a given the absorption in the receiving room it is recommended partition is obtained from the standard curve which (BS 5821: 1984) that the measured level difference is when comparedwith the measured SRI values produces

.

60 50 0

.lJ

U

OH .IJW

40

43

JL

(flW

00)

30

0 4E 0

20

I

JIj

rl 0

>

1.0

0

0

Il

, ,z 1ii1: 20

10

30

40

50

Difference in Sound Reduction Indices (Higher — Lower)

Figure5.5 Sound reduction indices loss

60

1.0 1.

.1 .01. • 001

.0001

Technical information

143

an adverse deviation as close to —32dB as possible. Only Direct sound field: The direct sound field refers to the the SRI values which fall below a particular standard acoustic energy that arrives at a listener directly from the

curve are considered in the sum. Positive deviations source without any reflections from nearby surfaces or from the standardcurve are not taken into account. The objects. standardvalues for the curve corresponding to an R of Early decay time, EDT: This is the time in seconds, 52 are multiplied by six, which the sound in an enclosure takes to Reference value (dB) decay by 10dB from its equilibrium value. It is thoughtto Frequency (Hz) be important in determining the quality of auditoria, 100 33 especiallyfor music. The EDT is sometimes referred to as 125 36 the subjective reverberation time. 150 39 Noise reduction coefficient, NRC: This is the average, to 200 42 45 the nearest multiple of0.05, ofthe absorption coefficients 250 48 measured in the octave bands centred on 250, 500, 1000 315 400 500 630 800 1 000 1 250 1 600

51

and 2000Hz.

52 53

Normalroom modes: Sound waves in an enclosure travel around in all directions being reflected obliquely off the walls. Some paths repeat themselves continuously, formingwhat are known as normal modes. The normalmodesoccurat specificfrequencies related to the dimensions of the room. For a rectangular room the frequencies are given by

54 55

56 56 56 56 56

2000

2500 3150

The R value is the value in decibels of the reference curve at 500 Hz.

fn =

2

1/ V

(2 \1i (2 \'i +

+

(n2

,

\LLJ

where c= velocity ofsound (mis),

ç and are the room dimensions (m), and and n7 can independently n.7 have values 0, 1, 2, If the source containsfrequencies equal to the normal mode frequencies, resonances occurand large variations in sound level throughoutthe room can result especially at low frequencies. This is generally to be avoided. Norris—Eyringequation: Thisequationisamodified form of the Sabine equation and is suitable for use when the Sound in enclosedspaces average room absorption coefficient is greaterthan 0.1. Absorption: Absorption is the term applied to the process 0.161V by which energy is removed from a sound field. Most 5 materials will, to a greater or lesser extent, absorb sound, —2.3 X Slog10 (1 —) i.e. convert the acoustic energy into heat. However, to be a goodabsorber a material should generallyhave an open Reverberance: When a sound source, in an enclosure, is surface structure which allows sound to enter and turned off, the sound does not immediately stop but internally it should provide many interconnecting path- persists for a short time due to the reflection of energy ways through which the sound may pass to dissipate its from the walls ofthe enclosure. Similarly, it takes a finite energy. Good fibrous absorbents are glass fibre and time for sound to reach its equilibrium value after the source is turned on. This behaviour is known as reverbermineral wool. In acoustics absorption, A, has a morespecific meaning. ance andit is a majorfactorin determining the level and It is the product of the area, 5, of an absorbing material quality of sound in any enclosed space. and its absorption coefficient a. So Reverberant sound field: This is the sound fieldwithin an enclosure due to the continual reflections of the sound A = S X m2 or Sabines. from the walls of the enclosure. Air absorption: The absorption of sound by air is energy significant for propagation over long distances and in Reverberant sound pressurelevel: The steady value of the largeenclosures. High frequencies are absorbed the most sound pressure level through the body of an enclosure, and the absorption is dependent upon both temperature and away from the sound source, is referred to as the reverberantsoundpressurelevel,L.,.Its value will depend and humidity. the sound power, R of the source and the total Diffuse sound field: When the sound energy in an upon A, within the enclosure absorption, enclosure is uniform throughout the space, the sound = 10 log F— 10 log A + 126dB field is said to be diffuse. This is normally the case for 14,:,Ienclosures with conventional aspect ratios and small or absorption which is uniformly distributedthroughout the — 10 enclosure. log A + 6dB 1pr =

To obtain other reference curves the one-third octave band values are changedin 1 dB steps up or down. To obtaina Weightedstandardized level difference, single figure rating value from field measuredvalues of the standardized level difference, DT, the one-third octavevalues are weighted usingthe same methodused to obtain the airborne sound insulation indexrating, R.

n,

D:

a

L

Acoustics in the Built Environment

144

Reverberation time: The time which is taken for the reverberantsoundenergy in an enclosure to decay to one millionth of its equilibrium value, i.e. by 60dB, after the source is turned off, is known as the reverberation time. The reverberation time is frequency dependent and it is customary to measure its value in octave or one-third octave bands. There are a number ofsimple equations for predicting reverberation times. Room radius: For a source operating in an enclosure there are two soundfields, the reverberant and the direct, and the value of the sound pressure level at any point is the sum, that is the decibel sum, of the direct and reverberantsoundpressurelevels. Far from the source the reverberantfield will dominatewhile close to the source the direct field will be greatest. The distance, r, from the source where the direct and reverberant sound pressurelevels are equal is known as the room radius and it can be found from

r=-J

y l6lT

Sound absorption coefficient: The sound absorption coefficient is the quantity used to describe how well a particular material absorbs sound. It is denoted by a and is defined as Sound energy not reflected from material Sound energy incident upon material

For a perfect absorber a would have a value of 1 while for a perfect reflector a would equal zero. The absorption coefficient varies with frequency and also with the angleatwhich the sound strikes the material. Because ofthe angulardependenceit is usual to measure the absorption coefficient of materials in diffuse sound fields so that sound effectivelystrikes the material at all angles of incidence. The absorption coefficient measured under theseconditions is known as the randomincidence sound absorption coefficient and is denoted by It is usually measured in one-third octave or octave bands. There is no accepted way of obtaining the octave band value from the one-thirdoctave band values. The average of the three values or the highestvalue are both used.

.

where Q = source directivity factor, and A = room Assessinginternal spaces absorption. Articulation index, Al: The articulation index is a weighSabine equation: The Sabine equation gives the reverbera- ted fraction representing, for a given speech channeland tion time in terms of the room volume and total room noise condition, the effective proportion of the normal absorption as speech signal that is available to a listener for conveying speech intelligibility.It is obtainedfrom measurements or 0.161 V estimates of the speech spectrum and of the effective T= s A

if Vis in cubic metres and A in square metres.

The equation is valid for diffuse sound fields only and gives the best results when the average absorption coeffficient is less than 0.1. However,it is often usedwhen this condition is not met. For large enclosures air absorption is included so that T= where

0.161 V A + 4 mV

80

0'I x

70

UI

L 60 U)

m is a soundattenuation. Coefficient values for 4 m

as given

UI

a

in Table 5.4.

-l UI

50

> UI

I

Table 5.4 Air absorption (values of4mV in m2 unitsfor a volume of 100m3 at 20°C)

UI

40

L 3 UI UI UI

30

L

a

Relative humidity (%) Frequency

(Hz)

20

30

40

50

60

70

80

t 20 C 3

0

U)

125

250 500 1 000 2 000 4 000 8 000

0.06 0.14 0.25 0.57 1.78 6.21 19.00

0.05 0.13 0.25 0.47 1.21

4.09 14.29

0.04 0.12 0.26 0.46

10

0.04 0.03 0.03 0.02 0.11

0.10 0.26 0.26 0.46 0.48 1.00 0.90 0.88 3.10 2.60 2.27 11.00 8.95 7.61

0.09 0.25 0.50 0.88 2.08 6.69

0.08 0.25 0.51 0.88 1.95 6.04

UI

8 0 I')

ID

8 l fli

0 U)

0 0

(U

In

0

0 0 1

0 0 0

0 0 0

(U

'UI

Octave Band Centre Frequency Figure 5.6

Noue criterion curves

0 0 0

0 (Hz)

145

Technical information

masking spectrum of any noise which may be present along with the speech at the ear of the listener. If the Al is zero then there will be no understanding while if the AT is one there will be complete

-' 130

intelligibility.

0 'I

S3.5.

B

Balanced noise criterion curves, NCB: These are a set of curveswhich have been proposedas an update ofthe NC curves. They are not asyet generally accepted. Details can be found in a paper by Beranek, Balanced Noise Criterion Curves,j Acoust.Soc.Am., 86(2),August 1989,pp.650—664. Noisecriterion, NC: The conceptofthe noise criterionwas originally developed in the United States specificallyfor application in commercial buildings. Its calculation is based onan octaveband analysis ofa noise andreference is madeto a setofcurves whichare shown in Figure 5.6. The noise criterion is obtained by plotting the octave band soundpressurelevelsonto the reference curves and determining the lowest curve which is nowhere exceeded by the plotted octave band levels. Noise rating number, NR: The noise rating number is a single figure index obtainedfrom an octave band analysis of a noise. To obtain the NR number the octave band sound pressure levels are plotted onto a set of reference curves which are shown in Figures 5.7 and 5.8. The highestNRcurve that is intersected by the curve forming the plotted sound pressure levels gives the noise rating number. The octave band sound pressure levels are normallyjoined by straight lines.

ii L

Details ofthe calculation methodcan be found in ANSI

ci.

U

130 125

0

tao 115 ato 105

'C

I)

too

C.

.5

I0

U

go

e1

•0

I, >

75 70

.5

0

I

.5

I,

50 55 50 45 40 55 30 25 20

C-

U U

I' C.

a U

0

UI

15

U

to

0

5 0

—io, ,1 In

ID

(U

U

0)

0 Ii

0 0

i

00 0 (U

Octeve Sand Centre Frequency Figure 5.7 Noise rating curves (octave band)

0 00

0 00 5 (Hz)

110

100

S

( II

%

S

::: :::_ —

S

130

. —

c

S

—

—

S

S

30

S

S

S

20

JR too NA go

—

go

—

40

NA 105

—

•.

S

S

—

. —

c

NR 05 — —

•0

—

—

—

NA 55

-

-

—

—

,-.,4 50

-

- NA 45

: NI 40

0

U

to —10

.'.r 70

—

10 D

NA .5 •0 NP 75

—

..-,.

s _ .. S

—

—

is

M ItO

—

S

50

NA I

—

S

\ ,,,,

70

10 60 It

-- -.

;;—;

80 >

i30 NA 125

—

90 'S

to

'-I

•

'--

120

'C

•

a.

cli

140

) I

—

NA 35 NA 30 NA 25 NA 20 NA 15 NA 10 NA 5 NA 0

II•Eewoo'coe.,oopoonooonoooo L) (. II U U 0 II a.) a) 0 0 0 0 0 0 0 0 0 0 0 0 1 In

Third

Octave Band Centre Frequency

(Hz)

Figure 5.8 Noiserating curves (one-thirdoctave band)

Preferred noise criterion, PNC: The preferred noise criterionis very similar to the noise criterion in concept. However, the set of curves from which it is obtained extend to a lower frequency than that of the noise criterion curves and more emphasis is placed on low frequency noise. The curves for PNC are shown in Figure 5.9. PNC is not widely used, except for low-value curves e.g. in concert halls. RASTI: Rapid speech transmission index (RASTI) is a method for the objective measurement of the speech

transmission index. By restricting the number of noise bands to two and modulation frequencies to five in the calculation, rapid assessments of room speech intelligibility can be made; see Chapter 4. Room-noise criterion, RC: This is a single figure rating, used for assessing heating, ventilating and air-conditioning systems. The RCvalue is obtained by comparing noise levels, made in unoccupied rooms with all systems operating, with a set ofcurves. In additionthe RC number is classifiedinto four categories dependingon the overall shape of the spectrum. It is used as an alternative to NC. Details of how to calculate RC values can be found in the ASHRAE Handbook. Speech interferencelevel: Speech interference level is a simple-to-estimatemeasure of the masking of speech by noise. It is derived by taking the arithmetic average of the noise levels in the fouroctavebandscentred on 500, 1000, 2000 and 4000Hz.

146

Acousticsin the Built Environment

The standardcurves are identical to the Lw.. curves and the hG is equalto 110 minus the sound level at 500 Hz on the selected standard curve.

no a-

= 110 — JIG

0

.i 70 x 01

L 60 B C r1 a > a -J

50

II

'I

See ASTME E492—86and E989—84. PNC65 PNC no PNC 55 PNC

Impact noise level, L: This is the sound pressure level, measured in a one-third octave band, when a standard tapping machine is operating on the floor above the room.

Impact sound: Impact sound refers to sound produced when a short duration impulse, such as a footfall, acts

directly on a structure. The frequency content of the soundwill depend upon PNC 40 the duration of the impact; a short sharp event giving a broadband frequency content while a longer duration ao PNC n L event caused, for example, by having a resilient layerover a PNC 30 the structure, will contain mainly low frequency sound C C 20 and will be subjectivelyless disturbing. PNC25 0 U) Normalized impact noise level, L,: The impact noise level PNC20 as measured in the laboratory will depend upon the 10 PNC is C acoustic characteristics of the receiving room so to B normalize results the measured noise levels are corrected to a constant10 m2 of absorption. 0 Ui ('1 Ui 0 0 0 0 0 0 U) (U Ui 0 0 0 0 0 = L— 10 log A/A0 Hence .-I (U U) 0 0 0 0 •1 (1 B A = actual sound absorption in the receiving room in the Octave Band Centre Frequency (Hz) one-thirdoctave band under consideration. 5.9 noise criterion curves Figure Preferred A,1, = 10m2 L'0 is used if flanking transmission cannot be eliminated. Speech transmission index, STI: The speech transmission See BS 5821, Part2. indexquantifies the effect ofa sound transmission system on speech intelligibility.It is based upon an analysisof the Resonant frequency, J: The resonant frequency of an reduction in intensitymodulationofa signal which occurs isolator of stiffness K (Nm1) which supports a mass M along the transmission path from source to receiver. The (kg) is analysis is carriedout for 8 octavebands ofnoise, typically 125 Hz to 8kHz, and 14modulation frequencies. The .Hz results of this analysis are then combinedandnormalized 2'rr V M to give thespeech transmissionindexwhich hasavalue of1 for perfect transmission and a value of 0 for no signal This is often re-written as recognition. 15.8 Relationshipsexist between the STI values,the signal-tonoise ratio and the reverberation time of an enclosure, r fl\/ d allowing theoretical calculations to be made of the STI value. This is most useful at the design stage ofaproject. dbeing the static deflection (inmm) ofthe isolator when Details may be found in Bruel and Kjaer Technical the mass Mis placed on it. Review 3. For rubber isolators the constantbecomes 19.5. For an isolator to be effective its resonant frequency Impact soundand vibration must be at least three times lower than the lowest Impact insulation class, IIC: This is a single number frequency to be isolated. rating, used in the United States, which permits easy comparison of the impact isolation performanceoffloor/ Standardized impact sound level, LT: This is the impact ceiling assemblies. Impact sound levels normalized to a sound level measured between two rooms under field room absorption of 10 m2 are compared with a set of conditions and standardized to a reverberation time of standardcurves to producethe impactinsulation class. 0.5s, The calculation is exactlythe same as that described to T determine the weighted normalized impact sound presi.e. L'OT = L' — 10 log sure level, L,, except that in additionto the total adverse 0.5 deviation being less than or equal to 32dB, no one deviation must exceed 8 dB. L' = measured impact noise level. OJ

L

U:

40

l

(

I

f=—/—

Technical infonnation

See BS 5821, Part 2: 1986 and BS 2750, Parts 6 and 7: 1980.

Standard tappingmachine: A standardtapping machineis used to rate the impact noise isolation of floors. The machinehas five hammers, each of mass 0.5kg, equally spaced along a line. The hammers are dropped, from a height of 4cm, successively to give 10 impacts per second. Transmissibility:The effectivenessofa vibration isolator is measured in terms of its transmissibility. Two types of transmissibilityare generally defined: (1) Force transmissibility which is the ratio of the force transmitted by the isolator to the force applied to the structureon top ofit; (2) displacement transmissibilitywhich is the ratio of the displacement transmitted by the isolator to the displacement appliedat its base. In both cases the transmissibility, 7 is, for lightly dampedsystems, given by

Acceleration is what is commonly measured to quantifr the vibration of a surface. Vibration displacement, d: When an object vibrates, its surface will oscillate about its stationary position. These changes represent the vibration displacement. Vibration isolation: Vibration isolation is a means of reducingthe transmission of vibrating motions or forces from one structure to another. It is usually achieved by separating the two structures by an elastic element,known as a vibration isolator. Vibration velocity, v The velocityof a vibrating surface is related to the displacement by

v= v(m/s) = d(m) X o(rad/s) wherew = angular frequency.

T=

147

J(f/f)2 fis the frequency of vibrating motion andJr is the resonant frequency of the isolator together with the

I, L:

This is Weightednormalized impact sound level, a obtained from one-thirdoctave figure descriptor single where values of the normalized impact sound levels L, (laboratory) or L' (field). The normalized levels are compared structure mounted on it. The variation of the transmissi- with a set of weighting curves and the curve found for bility with frequency is shown in Figure 5.10. which the total adverse difference between the normalVibration acceleration, a: The acceleration of a vibrating ized levels and the curves is less than but as close to 32dB as possible. Adverse differences occur when the normalsurface is related to the displacement and velocityby ized levels fall above the rating curve. a = dw2 = The weighted normalized impact soundpressure level is the sound pressure level at 500 Hz on the standardcurve, which meets the above criterion. For an LNW or L'NW of 60 jo the curve is defined by >' 4J

5 2

m m

E m

1

C

ii

C.

I-

.5

C m

E U m

.2

ri

a U .1

.1

0 C

0 S

05

U

iJ \

C-

0 Li.

.02 .01

.1

______

.2

Ii

.5

1

2

Frequency

mm

N

.1 05 0

5

Ratto of Forcing Frequency to Natural Frequency Figure 5.10

Transmissibility

.5

10

100 125 160 200 250 315 400 500 630 800

Level (dB) 62 62 62 62 62 62 61

1250

60 59 58 57 54

ioo 1 600

51

2000

48

2500

45

3150

42

Other curves are obtainedby moving the one-third octave band values up or down in 1 dB steps. See BS 5821, Part 2 and BS 2750, Parts 6 and 7.

,

Weightedstandardized impact soundlevel, L',1. Thisis a single figure descriptor obtained from one-third octave band values of the standardized impact sound levels, L'IIT, w It is obtained in exactly the same way as the weighted normalized impact sound level, L.,. See BS 5821, Part 2 and BS 2750, Parts 6 and 7.

148

Acoustics

in the Built Environment

Equivalent Standards Assessinge,wironmental noise

BS 4142: 1990

ASTM E1014—84

BS 5228: 1984/1994

ISO 1966: 1986 ISO 2204: 1979 ISO/DP 7196

DIN 18005: 1987 DIN 45641: 1976/1987 DIN 45642: 1974 DIN 45643: 1984 DIN VDI 2714: 1988 DIN YDI 3723: 1982 DIN VDI 2718: 1975

NF S30—010: 1974 NF S30—008: 1984 NF S31—010: 1987 NF S31—050: 1987 NF S31—110: 1985

Rating ofperformance ofbuilding BS 5821: 1984 ASTM C1071—86

ANSI S3.23: 1980 ANSI S12.4: 1986

ISO 717: 1982

ASTM E413—73 ASTM E989—84 DIN 52210: 1984 NF P05—321: 1096 NF S31—057: 1982 Measurement ofimpactinsulation BS 2750: 1980 ASTM E492—77

ISO 140: 1980

ASTM E1007—84 DIN 52210: 1984 NF S31—052: 1979 NF 531—053: 1979 NF S31—056: 1982 Measurement ofsoundpower BS 4196: 1986

DIN 45635: 1985

ASTM E1124—86

ISO 3740: ISO 3741: ISO 3742: ISO 3743: ISO 3744: ISO 3745: ISO 3746: ISO 3747:

1980 1988 1988 1988 1981 1977 1979 1987

ANSI 81.23: 1976 ANSI 81.30: 1985 ANSI S1.31: 1986 ANSI S1.32: 1986 ANSI S1.33: 1982 ANSI S1.35: 1985 ANSI S1.36: 1979 ANSI S2.34: 1988

ISO 7779: 1988

ANSI S12.10: 1985

NF S31—025: 1977 NF S31—026: 1978 NF S31—027: 1977 NF S31—022: 1989 NF S31—024: 1989 NF 831—067: 1986

Noise emissionfrom computers and business machines ECMA 74: 1981 ECMA 109: 1985

DIN YDI 3729: 1982 Sound jorcementsystems BS 6259: 1982 BS 6840: 1987 DIN 45589: 1979

IEC 268: 1985

ISO 9296: 1988

Technical informabon

Speech andnoise ISO/TR 3352: 1974

DIN 18041: 1968 DIN 45621: 1973

ASTM E1041—85

ANSI S3.2: 1960 ANSI S3.5: 1969 ANSI S3.14: 1977

ASTM E1110—86 ASTM E1130—88

NF S31—047: 1975 NF S32—001:1975 NFXS5—108: 1987

IEC 84(CO)2: 1986

-

Vibration measurementandresponse BS 6177: 1982 BS 6472: 1984 BS 6841: 1987 BS 6611: 1985

ISO 2017: 1982 ISO 2631: 1985 ISO 5805: 1981 ISO 6897: 1984 ISO 7849: 1987 ISO 4866: 1986 ISO 8569: 1989

DIN 4150: 1986 DIN 45669: 1981/1989 Mechanical services BS 848: 1985 BS 4718: 1971

DIN 45646: 1988 DIN VDI 2081: 1983 DIN 45635: 1986 DIN VDI 3731: 1982

ANSI S3.18: 1979 ANSI S3.29: 1983 ANSI S3-W-39

VDI 2057: 1987 ASTM E477-84

NF E51—701:

1980

NF P50—402:

1985

ANSI S12.11: 1987

NF E51—706: 1988 NF S31—021: 1982 NF S31—046: 1988

Soundinsulation in buildings BS 8233: 1987 DIN 4109: 1989 DIN 18165: 1987 DIN VDI 2569: 1990 DIN VDI 2571: 1976 DIN VDI 2711: 1978 DIN VDI 2719: 1987 DIN VDI 3728: 1987

ISO/DIS 6242: 1989

Acousties qrbuildings

NF P90—207: 1987 Instrumentation BS 2475: 1964 BS 3593: 1986 BS 5969: 1981 BS 6698: 1986

DIN 45401: 1985 DIN 45651: 1964 DIN 45652: 1964 Terminology

BS4727: 1985

IEC 196: 1965 IEC 225: 1966 IEC 651: 1979 IEC 804:

ANSI ANSI ANSI ANSI ANSI ANSI

ISO 31—7: 1978 ISO 131: 1979

ANSI S3.32: 1982

1985

NF S30—002: 1972 NF S31—109: 1983

ASTM C634-86

BS 5775: 1979 DIN 1320: 1990 DIN 45630: 1971 DIN 52217: 1984

ISO 266: 1975

IEC 50(801): 1984

NF S30—004: 1966 NF S30—101: 1973

NF S30—102: NF S30—103: NF S30—106:

1973 1973 1975

NFXO2—207: 1985

S1.4: 1983 S1.4: 1985 S1.6: 1984 S1.11: 1986 S1.13: 1971 S1.42: 1986

150

Acousticsin the Built Environment

Measurement ofreverberation time

BS 5363: 1986 DIN 52216: 1965 Measurement

NF S31—012:

1973

ofabsorption coefflcientc

BS 3638: 1987 DIN 52212: 1961 DIN 525215: 1963 Measurement

Iso 3382: 1975

ASTM C423—89

ISO 354: 1985

NF S31—065: 1981

ofsound insulation

BS 2750: 1980

ASTM E90—83 ASTM E336-84 ASTM E596-78 ASTM E966-84 ASTM E1222—87

DIN 52210: 1984

NF S31—045: 1989 NF S31—051: 1985 NF S31—049: 1982 NF 534—054: 1982 NF S34—055: 1982

ISO 140: 1980

Internationalstandards

InternationalElectrotecilnicalCommission(IEC) lEG 50 Internationalelectrotechnical vocabulary. 801: 1984 Vocabulary: acoustics and electoacoustics. lEG 84 (GO) 2: 1986 sound system equipment; report on the RASTI

method for the objective rating of

speech intelligibilityin auditoria; (Central Office) 2.

lEG 196: 1965 lEG 225: 1966

lEG standard frequencies. Octave, half-octaveandthird octaveband filters intendedfor the analysis ofsoundsand vibrations.

lEG 268

Sound system equipment

Part 1: 1985 Part 2: 1971 Part 4: 1972 Part 5: 1989 Part 7: 1984 Part 16 Draft lEG 651: 1979 lEG 804: 1985

General Explanation of general terms Microphones Loudspeakers Headphones

Report on the RASTI auditoria. Soundlevel meters Integrating

—

ISOStandards ISO 31—7: 1978 ISO 131: 1979

Quantitites

ISO 140

Acoustics

Part 1: 1978 Part 2: 1978 Part 3: 1995 Part 4: 1978 Part 5: 1978 Part 6: 1978 Part 7: 1978 Part 8: 1978 Part 9: 1985

Acoustics air.

—

method

for the objective rating of speech intelligibility in

averaging sound level meters.

and units of acoustics. — expression of physical and subjective magnitudes of sound or noise in

— measurement of sound insulationin buildings and building elements. Requirements for laboratories. Statementof precision requirements. Laboratory measurements of airborne sound insulation of building elements. Field measurements of airbornesound insulation between rooms. Field measurements of airbornesound insulation of facade elements and facades. Laboratory measurements of impact sound insulationoffloors. Field measurements of impact sound insulation of floors. Laboratory measurements of the reduction of transmitted impact noise by floor coverings on a standard floor. Laboratory measurements ofroom-to-room airborne sound insulation ofsuspended ceiling with a plenum above it.

Technical information

Iso 266:

ISO 354: 1985

Acoustics — preferred frequenciesfor measurements. Acoustics — measurement of sound absorption in a reverberation room.

ISO 389: 1991

Acoustics:

1975

151

standard reference zero for the calibration of pure tone air conduction

audiometers.

— rating of sound insulation in buildings and of building elements. Airborne sound insulation in buildings and of interior building elements. Impactsound insulation. Airborne sound insulation of facade elements and facades.

ISO 717

Acoustics

ISO 1996

Acoustics — description and measurement Basic quantities and procedures.

Part 1: 1996 Part 2: 1996 Part 3: 1982 Part 1: 1982 Part 2: 1987 Part 3: 1987

of environmental noise.

ISO 2017: 1982

Acquisition of data pertinent to land use. Application to noise limits. Vibration and Shock — Isolators: procedurefor specifiing characteristics.

ISO 2204:

Acoustics

ISO 2631

Evaluation of human exposure to whole bodyvibration. General requirements. Evaluation of exposure to whole bodyz-axis verticalvibration in the frequency range 0.01 to 0.63Hz.

Part 1: 1985 Part 3: 1985 ISO/TR 3352: 1974 ISO 3382: 1975 ISO 3740: 1980

— guide to International Standards on the Measurement of airborne acoustical noise and evaluation of its effects on human beings.

Acoustics — assessment of noise with respect to its effect on the intelligibility of speech. Acoustics— measurement of reverberation time in auditoria. Acoustics— determination ofsound power levels of noise sources: guidelines for the use ofbasic standards and for the preparationof noise test codes.

ISO 3741: 1980

Acoustics — determination of sound power levels of noise sources: precision methods for broad band sources in reverberation rooms.

ISO 3742: 1988

Acoustics— determinationofsound power levels ofnoise sources:precision methods of discrete frequency and narrow band sources in reverberation rooms. Acoustics— determination ofsound power levelsofnoise sources:engineeringmethods for special reverberation test rooms. Acoustics— determination ofsound power levels ofnoise sources:engineeringmethods for free-field conditions over a reflecting plane. Acoustics — determinationof sound power levels of noise sources: precision methods for anechoic and semi-anechoic rooms.

Iso 3743: 1988 ISO 3744: 1981 ISO 3745: 1977 ISO 3746: 1979 ISO 3747: 1987

ISO/DIS4866: 1995 ISO 4871: 1984 (new version in preparation) ISO 5805: 1981

Acoustics— determination of sound power levels of noise sources: survey method. Acoustics— determination of sound power levels ofnoise sources: survey methodusing a reference sound source. Mechanical vibration and shock: measurementand evaluation ofvibration effects on buildings; guidelines for the use ofbasic standard methods. Noise labelling of machinery and equipment. Mechanical vibration and shock affecting man: vocabulary.

ISO 6897: 1984

Guidelines for the evaluation of the response of occupants of fixed structures, especially buildings and off-shore structures, to low frequency vibration horizontal motion (0.063 to 11 Hz).

ISO/DIS6243 Part 3: 1989

Building construction: expression ofusers' requirements. Acoustical requirements. Acoustics— measurement procedures for ductedsilencers.

ISO 7235: 1991 ISO 7779: 1988

Acoustics — measurement of airborne noise emitted by computer and business equipment.

152

Acoustics in the Built Environment

ISO/TR 7849: 1987

Iso 8569: 1989 ISO 9296: 1988

Acoustics — estimation of airborne noise emitted by machinery using vibration measurement. Mechanical vibration: shock-and-vibration-sensitiveelectronicequipment; methods of measurement and reportingdata of shock and vibration effects in buildings. Acoustics — declared noise emission values of computer and business equipment.

EuropeanComputer Manufadums Association ECMA 74: 1981 Measurement of airborne noise emitted by computers and business machines. ECMA 109: 1985

Declared noise emission values of computerand business equipment.

GemianNational Standards DIN 1320: 1990

Acoustics: terminology.

DIN 1800: 1987

DIN 1804: 1968 DIN 18165: 1987 DIN 4150: 1986 DIN 4109: 1989 Beiblatt 1 Beiblatt 2 DIN 45035: 1980 DIN 45401: 1985 DIN 45589: 1979 DIN 45621: 1973 DIN 45630: 1971 DIN 45635: 1985 DIN 45635: 1986 DIN 45635: 1985 DIN 45635: 1986

Teil 1. Noise abatementin town planning; calculation methods. Teil 1, Beiblatt 1. Noise abatement in town planning; acoustic orientationvalues in town planning. Acousticalquality in small to medium size rooms. Teil 2. Fibre insulatingbuilding materials: impact sound insulating materials. Teil 3. Structural vibration in buildings: effects on structures. Sound insulation in buildings: requirements and verifications. Soundinsulation in buildings: construction examples and calculation methods. Soundinsulation in buildings: guidelines for planningandexecution; proposals for increased sound insulation; recommendations for sound insulation in personalliving and working areas. Teil 14. Noise measurement on machines: airborne noise measurement, enveloping surfacemethod, air cooled heatexchangers (air coolers). Acoustic, electroacoustic: standard frequencies for measurements. Requirements for congress microphones. Teil 2. Word listsfor intelligibilitytest. Teil 2. Sentence lists for intelligibilitytest. Teil 1. Physical and subjective magnitudes of sound. Teil 3. Measurement of airborne noise emitted by machines: engineeringmethod for special reverberation test rooms. Teil 38. Measurement of noise emitted by machines; airborne noise emission; enveloping surface method, reverberation room method and indirect methods; fans. Teil 46. Measurement of noise emitted by machines; airborne noise emission; enveloping surface method; cooling towers. Teil 56. Measurement of noise emitted by machines; airborne noise emission; enveloping surface methodand indirectmethod;fan assistedwarmair generators, fan assisted air heaters and fan units of air handlingdevices.

DIN 45641: 1976 DIN 45641: 1987 DIN 45642: 1974

Averaging of time varying sound level; ratinglevels. Averaging of sound levels; single eventlevel. Measurement of traffic noise.

DIN 45643: 1984

Teil 1. Measurement and assessment of aircraft noise; quantities and parameters. Teil 3. Measurement andassessment of aircraft noise; determinationofrating level of aircraft noise exposure. Measurement procedures for ducted silencers; insertion loss, transmission loss, flow noise, total pressureloss. Octave filters for electroacoustical measurements. Third octave filters for electroacoustical measurements.

DIN 45646: 1988 DIN 45654: 1964 DIN 45652: 1964

Technical infonuation

DIN 45669: 1981 DIN 45669: 1989 DIN 52210: 1984

DIN 52210: 1987

DIN 52210: 1984 DIN 52210: 1985 DIN 52210: 1989 DIN 52210: 1989 DIN 52212: 1961 DIN 52215: 1963 DIN 52216: 1965 DIN 52217: 1984 VDI 2057 Blatt 4.1: 1987 VDI 2081: 1983 VDI 2566: 1988 VDI 2569: 1990 VDI 2571: 1976 VDI 2711: 1978 VDI 2714: 1988 VDI 2718: 1975 YDI 2719: 1987 VDI 3720 Blatt 1: 1980 VDI 3720 Blatt 2: 1982 BDI 2723 Blatt 1: 1982

153

Teil 1. Measurementof vibration emission; requirements on vibration meter. Teil 2. Measurement of vibration emissions; measuring method; amendment1. Teil 1. Tests in building acoustics; airborne and impact sound insulation; measuring methods. Teil 2. Tests in building acoustics; airborneand impact sound insulation; laboratories for measuring of the sound reduction of building elements. Teil 3. Testing of acoustics in buildings, airborne and impact sound insulation; laboratory measurements of sound insulation of building elements and field measurements between rooms. Teil 4. Tests in building acoustics;airborneand impact sound insulation; determination of single-number quantities. Teil 5. Testing in building acoustics; airborne and impact sound insulation; field measurements of airborne sound insulation of exterior building elements. Teil 6. Testsin building acoustics;airborneandimpactsound insulation; determination of the level difference. Teil 7. Tests in building acoustics; airborneandimpact sound insulation; determination of the lateral sound reduction index. Testing of architectural acoustics; measurement of sound absorption coefficient in a reverberation room. Testing of architectural acoustics; determinationof sound absorption coefficient and impedance in a tube. Testing of architectural acoustics; measurementof reverberation time in auditoria. Test in building acoustics; flanking transmission; terms and definitions. Effect of mechanical vibrations on human beings; measurements and assessment for workshop places in buildings. Noise generation and noise reduction in air-conditioning systems. Noise reduction on lifts. Sound protection and acoustical design in offices. Sound radiation from industrial buildings. Noise reduction by enclosures.

Outdoor soundpropagation. Noise abatementin town planning. Sound isolation of windowsand theirauxiliary equipment. Noise abatementby design; general fundamentals. Noise abatementby design; compilation of examples. Application of statistical methods for the description of variating ambient noise levels.

VDI 3728: 1987 VDI 3729 Blatt 1: 1982 VDI 3729 Blatt 2: 1982

Airborne sound isolation of doors and movable walls. Characteristic noise emissionvalues oftechnical sound sources; office machines; basic directions. Characteristic noise emission values of technical sound sources; office machines, typewriters.

VDI 3729 Blatt 3: 1982 VDI 3729 Blatt 5: 1982 VDI 3729 Blatt 6: 1990 VDI 3731 Blatt 1: 1982 VDI 3731 Blatt 2: 1988

Characteristic noise emission values of technical sound sources; office machines, duplicating machines and copiers. Characteristic noise emission values of technical sound sources; office machines; mail processing (preparation) machines. Characteristic noise emissionvalues of technical sound sources; computer andbusiness equipment; computer. Characteristic noise emission values of technical sound sources; compressors. Characteristic noise emission values of technical sound sources; fans.

154

Acoustics in the Built Environment

at pipes.

VDI 3733:1983

Noise

VDI 3744: 1983

Noise control

American National Standards Institute ANSI S1.4: 1983 Specification

ANSI Sl.4a: 1985 ANSI S1.6: 1984 ANSI S1.11: 1986 ANSI 51.13: 1971 (R 1986) ANSI 51.23: 1976 (R 1983) ANSI 51.30: 1979 (R 1985) ANSI 51.31: 1980 (R 1986) ANSI 51.32: 1980 (R 1986) ANSI S1.33: 1982 ANSI 51.35: 1979 (R 1985) ANSI S1.35: 1979 (R 1985) ANSI S1.42: 1986 ANSI S2.8: 1972 (R 1986) ANSI 53-W-39

ANSI S3.2: 1960 (R 1982) ANSI S3.5: 1969 (R 1986) ANSI S3.14: 1977 (R 1986) ANSI S3.18: 1979 (R 1986) ANSI S3.23: 1980 (R 1986) ANSI 53.29: 1983 ANSI 53.32: 1982 ANSI 512.4: 1986 ANSI 512.9: 1988

in hospitals and sanatoriums; instructions for planning.

for sound level meters.

Sound level meters. Preferredfrequencies and band numbersfor acoustical measurements. Octave-band and fractional octave-bandanalogand digital filters. Methods for the measurements of sound pressure levels. Method for the designation of sound power emitted by machinery and equipment. Guidelines for the use of sound power standards and the preparation of noise test codes. Broad-band noise sources in reverberation rooms. Precision methods for the determination ofsound power levels. Discrete-frequencyand narrow-band noise sources in reverberation rooms, precision methods for the determination of sound power levels. Engineering methods for the determinationof sound power levels of noise sources in a special reverberation test room. Determination of sound power levels of noise sources in anechoic and semi-anechoic rooms. Survey methods for the determinationof sound power levels of noise sources. Design response of weighting networks for acoustical measurements. Guide for describing the characteristics of resilient mountings. Effects of shock and vibration on man. (A special report — not a standard.) Method for measurement of monosyllabicword intelligibility. Methods for the calculation of the articulation index. Rating noise with respect to speech interference. Guide for the evaluation of human exposure to whole-bodyvibration. Sound level descriptors for determination of compatible land use. Guide to the evaluation of human exposure to vibration in buildings. Vibration and shock affecting man, mechanical-vocabulary. Method for assessment of high energy impulsive sound with respect to residential communities. Quantities and procedure for description and measurement of environmental sound

(part 1).

ANSI 512.10: 1985 ANSI 512.11: 1987 ANSI 512.34: 1988

Methods for the measurement and designation of noise emitted by computer and business equipment. Methods for the measurement of noise emitted by small air-movingdevices. Engineering methodsfor the determination ofsound powerlevels ofnoise sources for essentiallyfree field conditions over a reflecting plane.

American Society for Testing and Materials Standards ASTM C 384—88 Test method for impedance

ASTM C 423—89

and absorption of acoustical materials by the impedance tube method. Test method for sound absorption and sound absorption coefficients by the reverberation room method.

Technical infonnation

ASTM C 634-86 ASTM C 1070—86 ASTM E 90—87 ASTM E 336-84 ASTM E 413-87 ASTM E 477-84 ASTM E 492-86 ASTM E 497—87 ASTM E 596—88 ASTM

E 597—81 (1987)

ASTM E 795-83 ASTM E 966-84 ASTM E 1007—84 ASTM E 1014—84 ASTM E 1041—85 ASTM E 1110—86 ASTM E 1124—86 ASTM

E 1130—88

ASTM E 1222—87 French Standards NF E51—701: 1980

NF E51—706: 1988 NF P05—321: 1986 NF P50—402: 1985

155

Definitions of terms relatingto environmental acoustics. Standard specification for thermal and acoustic insulation (mineral fibre, duct lining material). Method for laboratory measurement of airborne sound transmission loss of building partitions. Test method for measurement of airborne sound insulation in buildings. Classification for determination of sound transmission class. Method oftesting duct liner materials and prefabricated silencers for acoustical and air flow performance. Method of laboratory measurementof impact sound transmission through floor— ceiling assemblies using the tapping machine. Practice for installing sound-isolating gypsumboard partitions. Method for laboratory measurement of the noise reduction of sound-isolating enclosures. Practice for determining a single-number ratingof airbornesound isolation for use in multi-unit building specifications. Practices for mountingtest specimens during sound absorption tests. Guide for field measurement of airborne sound insulation of building facades and facade elements. Test method for field measurementof tapping machine impact sound transmission through floor—ceiling assembliesand associated support structures. Guide for the measurementofoutdoor A-weightedsound levels. Guide for measurementof masking soundsin open offices. Classificationfor determiningof articulation class. Test method for field measurement of sound power level by the two-surface method. Test method for objective measurement of speech privacy in open offices using articulation index. Test method for laboratory measurement ofinsertionloss of pipe-lagging systems.

Controlledmechanical ventilation components. Code for aerodynamic and acoustic testing of extract air terminaldevices. Controlled mechanical ventilation components. Code for aerodynamic and acoustic testings of extraction units for private houses. Simple flux. Performance standardin building. Presentation of the performances of facades made ofcomponents from the samesource. Ventilation components. Code for aerodynamic and acoustic testing of facade air inlets.

NF P90—207: 1986 NF S30—002: 1972 NF S30—004: 1966

Sporthalls. Acoustics. Acoustics.Standard frequencies for acoustic measurement. Acoustics.Expressing the physical andpsychophysiologicalproperties of a sound or a noise.

NF S30—008: 1984 NF S30—010: 1974 NF S30—101: 1973 NF S30—102: 1973

Guide to standards on the measurement of airborne acoustical noise and evaluation of its effects on human beings. Acoustics. NR curve for the assessment of noise. Acoustics.Terminology: generaldefinitions. Acoustics. Terminology: transmission systems and transducers for sound and vibrations. Acoustics.

156

Acoustics

NF S30—103: 1973 NF S30—106: 1975 NF S31—O1O: 1987

NF S31—012: 1973 NF S31—021: 1982 NF S31—022: 1989 NF S31—025: 1977 NF S31—026: 1978 NF S31—027: 1977 NF S31—045: 1989

NF S31—047; 1975 NF S31—049: 1982 NF S31—050: 1979 NFS31—051: 1985

NF S31—052: 1979 NF S31—053: 1979 NF S31—054: 1982 NF S31—055: 1982

NF S31—056: 1982

NF S31—057: 1982 NF S31—059: 1983 NF S31—065: 1981 NF S31—067: 1986 NF S31—109: 1983 NFS31—11O: 1985

in the Built Environment Acoustics. Terminology: instruments. Acoustics vocabulary: architectural acoustics.

Acoustics. Description and measurement of environmental noise: investigation of complaints against noise in inhabited areas. Acoustics. Measuring the period ofreverberation in auditoria. Acoustics. Platform measurement of the noise emitted by ducted fans. Reduced chamberon discharge method. Acoustics.Determination ofsound power levels ofnoise sources. Precision methodsfor broad-band sources in reverberation rooms. Acoustics.Determination of sound powerlevels of noise sources. Part 4: Engineering method for free fieldconditions over a reflecting plane. Acoustics. Determination of the sound power emitted by noise sources. Part V: Laboratory methods in anechoic and semi-anechoic rooms. Acoustics.Determination ofthe level ofacoustic power emitted by noise source. Part6: Control method for on-site measurements. Acoustics. Measurement of the acoustic insulation of building and building components. Laboratory measurement of insulation against airborne noise of small sized building components. Acoustics.Assessmentof speech intelligibility distances in noisy conditions. Acoustics.Measurement of the acoustic insulation of buildings and building components. Precision specifications. Acoustics. Measurement of the acoustic insulation of building and building components. Specifications relatingto laboratories. Acoustics. Measurement of the acoustic insulation of buildings and building components. Laboratory measurement of insulation against airborne noise of building components. Acoustics. Measurement of the acoustic laboratorymeasurementof transmission of impact noise by floors. Acoustics. Measurement of the acoustic insulation of building and building components. Laboratory measurementof the reduction in transmission of impact noise due to floor covering and floating floors. Acoustics. Measurement of the acoustic insulation of buildings and building components. Investigatorymethod for the in-situ measurement ofairborne soundinsulation between rooms. Acoustics. Measurement of the acoustic insulation of buildings and building components. Investigatorymethod for the in-situ measurement ofairborne soundinsulation of rooms from road traffic noise. Acoustics. Measurement of the acoustic insulation of buildings and building components. Investigatory method for the in-situ measurement of impact sound transmission. Acoustics.Verificationof the acoustic quality of buildings. Acoustics.Test code for the measurementof noise emitted by bar guide tubes (screw cutting industry). Acoustics. Testing of architectural acoustics. Determination of sound absorption coefficient and impedance in a tube. Acoustics. Determination ofsound power levels ofnoise sources. Part 7: Surveymethod

usinga reference soundsource. Acoustics. Integrating sound level meters.

Acoustics.Description and measurement ofenvironmental noise. Basic quantities and general evaluation methods.

Technical Infonnation

NF S32—001: 1975

NF X02—207: 1985 NF X35—108, NF ISO 7731: 1987

British Standards

BS 648: 1964 BS 848

Part2: 1985 Part6: 1989

157

Acoustics.Soundsignal for emergency evacuation. Fundamental standards. Quantities, units and symbolsofacoustics.

Dangersignals for work places. Auditory danger signals.

Schedules ofweights ofbuilding materials. Fans for general purpose. Methods of noise testing. Methods of measurement offan vibration.

BS 1042

Part 1: Various dates by section 1981 to 1993

Pressure differential devices.

Specification for octave and one-thirdoctave band pass filters. Measurement ofsound insulation in buildings and of building elements. Recommendations for laboratories Determination, verification and application of precision data. Laboratory measurements of airborne sound insulation of building elements. Field measurements of airbornesound insulation between rooms. Field measurements of airbornesound insulation of facade elements and facades. Laboratory measurements ofimpact sound insulation of floors. Field measurements of impact sound insulation of floors. Laboratory measurements of the reduction of transmitted impact noise by floor coverings on a standardfloor. Method for laboratorymeasurementof room-to-room airborne sound insulation of Part 9: 1987 a suspended ceiling with a plenum above it. BS 3593: 1986 Recommendation on preferredfrequencies for acoustical measurements. BS 3638: 1987 Method for measurement of sound absorption in a reverberantroom. Acoustics —Determinationofsound power levels of noise sources usingsound pressure: BS EN ISO 3746: 1996 survey methodusing an enveloping measurement surface over a reflecting plane. BS4142: 1990 (under review) Method of rating industrial noise affecting mixed residential and industrial areas. BS 4196 Soundpower levels ofnoise sources. Part 0: 1986 Guide for the use ofbasic standards and for the preparationof noise test codes. Precision methodsfor determinationof sound power levels for broad-band sources Part 1: 1991 in reverberation rooms. Precision methods for determinationof sound power levels for discrete-frequency Part 2: 1991 and narrow-band sources in reverberation rooms. Part 3: 1991 Engineering methodsfor determination ofsound power levels for sources in special reverberation test rooms. Part 4: 1981 Engineering methods for determinationof sound power levels for sources in free field conditions over a reflecting plane. Part 5: 1981 Precision methods for determinationof sound power level for sources in anechoic and semi-anechoic rooms. Part7: 1988 Survey method for determination of sound power levels of noise sources using a reference sound source. Part8: 1991 Specificationfor the performance and calibration of reference sound sources. BS 4718: 1971 Methods of test for silencers for air distribution systems. BS 2475: 1996 BS 2750: Part 1: 1980 Part 2: 1993 Part 3: 1995 Part 4: 1980 Part 5: 1980 Part 6: 1980 Part 7: 1980 Part 8: 1980

BS 4727: Part 3 Group 08: 1985 BS 4773: 1989

Part 2: 1989 BS 4856

Part 4: 1978 Part 5: 1979

Acoustics and electroacoustics terminology. Methods for testing and rating air terminaldevices for air distribution systems. Acoustic testing. Methods for testing and rating fan coil units, unit heaters and unit coolers. Acousticperformance,withoutadditionalducting. Acousticperformance,with ducting.

158

BS

Acoustics

in the Built Environment

Iso 4869

Part 2: 1994 BS 4857

Part 2: 1978 (1983) BS 5108

Part 1: 1991 BS 5135: 1995 BS 5228

Part 1: 1997 Part 2: 1997 Part 3: 1997 Part 4: 1992

BS 5363: 1986 BS 5502: Part 32: 1996 BS 5727: 1979 BS 5775, Part 7: 1979 BS 5793

Part 8: 1991 BS 5821

Part 1: 1984 Part 2: 1984 Part 3: 1984

BS 5969: 1981 BS 6083

Part 3: 1991

BS 6177: 1982 BS 6259: 1997 BS 6472: 1992 BS 6611: 1985

Part 1: 1986 Part 2 Sect 2.1: 1990

Acoustics

—

Hearing protectors. Estimation of effective A — weighted sound pressure levels when hearing protectors are worn.

Methods for testing and rating terminalreheat units for air distribution systems. Acoustic testingand rating. Sound attenuationof hearing protectors. Determination of sound power levels of noise from air terminaldevices. Noise and vibration control on construction and open sites. Code of practice for basic information and procedures for noise and vibration control. Guide to noise and vibration control legislation for construction and demolition including road constructions and maintenance. Code of practice applicable to surface coal extraction by opencastmethods. Code of practice for noise control applicable to piling operations. Method for measurement of reverberation time in auditoria. Buildings and structures for agriculture: Guide to noise attenuation Method for describing aircraft noise heard on the ground. Specificationfor quantities, units and symbols: Acoustics. Industrial process control valves. Noise conditions. Methods for rating the sound insulation in buildings and of building elements. Methodfor rating theairbornesoundinsulation in buildings andofinteriorbuilding elements. (Superceded by BS ENISO 717/1 1997 at 1/9/1997) Method for rating the impact sound insulation. (Superceded by BS ENISO 717/2 1997 at 1/9/1997) Methodfor ratingthe airborne sound insulation offacade elements and facades. Specificationfor sound level meters.

Hearingaids. Methods for measurement of electroacoustical characteristics

of hearing

aid

equipment. Guide to selection and use of elastomeric bearings for vibration isolation of buildings. The design, planning, installation and maintenance of sound systems.

Guide to evaluation of human exposure to vibration in buildings (1Hz to 80 Hz). Guide to evaluation of the response of occupants of fixed structures, especially buildings and offshore structures, to low-frequencyhorizontal motion (0.063Hz to 1 Hz).

Methods for determination of airborne acoustical noise emitted by householdand similar electrical appliances.

Part2 Sect 2.2: 1990 Part2 Sect 2.3: 1991 BS 6698: 1986 Amd 1: 1991

Specification for integrating-averagingsound level meters.

BS 6840 Part 1: 1987

Sound system equipment. Methods for specifyingand measuring general characteristics used for equipment performance. Glossaryof general terms and calculation methods. Methods for specifring and measuring the characteristics of sound system amplifiers. Methods for specifyingand measuring the characteristics ofmicrophones. Methods for specifyingand measuring the characteristics ofloudspeakers.

Part 2: 1993 Part 3: 1989 Part 4: 1987 Part 5: 1995

Technical infonnation

Part 6: 1987

Part 8: 1988

159

Methods for specifying and measuring the characteristics of auxiliary passive elements. Methods for specifyingand measuring the characteristics of automatic gain control devices.

Methods for specifyingand measuring the characteristics of artificial reverberation, time delay and frequency shift equipment. Part 11: 1988 Specification for application of connectors for the interconnection of sound system components. Part 12: 1995 Specification for applications of connectors for broadcast and similar use. Part 13: 1987 Guide for listening tests on loudspeakers. Part 14: 1987 Guide for circularand elliptical loudspeakers; outer frame diameters andmounting dimensions. Part 15: 1988 Specification for matching values for the interconnection of sound system components. Part 16: 1989 Guide to the 'RASTI' method for the objective rating of speech intelligibility in auditoria. Part 18: 1996 Guide for digital peak level indicator. BS 6841: 1987 (under review) Guide to measurementand evaluation of human exposure to whole body mechanical vibration and repeated shock. BS 6912: Part 3: 1990 Safetyof earth-moving machinery — sound test methodfor machine-mounted forward and reverse warning signal. BS 6926: 1995 Determination of sound powerlevels of noise sources. BS 7385 Evaluation and measurement for vibration in buildings. Guide for measurement ofvibrations and evaluation of their effects on buildings. Part 1: 1990 Part 2: 1993 Guide to damage levels from groundbornevibration. BS 7443: 1991 Specificationfor sound systemsfor emergency purposes (IEC 849) (largely updatesBS 5839 'Fire detectionand alarm systems for buildings'). BS 7445 Description and measurementof environmental noise. Part 1: 1991 Guide to quantities and procedures. Part 2: 1991 Guide to the acquisition of data pertinent to land use. Part 3: 1991 Guide to the application to noise limits. Test code for the measurement of airborne noise emitted by rotating electrical BS 7458 machinery. Part 1: 1991 Engineeringmethod for the free-field conditions over a reflecting plane. Part 2: 1991 Survey method. Code of Practice for Audio-FrequencyInductionLoop Systems(AFILS). BS 7594: 1993 Shortened procedurefor type 2 sound level meters. BS 7580, Part 2: 1995 BS 7636: 1993 Method of determination of thresholds of hearingusing sound field audiometrywith pure tone and narrow-band test signals. BS 7643, Part 3: 1993 Building construction: expression of users' requirements: Acousticalrequirements. BS 7698, Part 9: 1996 Measurement and evaluation of mechanical vibrations. Acoustics — Determination of sound power levels of noise sources using sound BS 7703, Part 1: 1993

Part 9: 1987

intensity.

BS 7827: 1996 BS 8233: 1987 BS 8297: 1995

Code of Practice for designing, specifying, maintaining, and operating emergency sound systems at sports venues Code of Practice for sound insulation and noise reduction for buildings. Determination of sound power levels of multi-source industrial plants.

Page blank in original

Index

A-weighting, 136

Abatement notice, 27, 33 Absorbers, fibrous,50 Absorption, 48, 53, 54, 143 Absorption coefficients,50, 51—2 Acceleration, 29 Accelerometer, 12 Acoustic appraisal, 13 Acoustic canopies, 64 Acoustic curtains, 102 Acoustic doorsets, 99 Acoustic laboratories, 52 Acoustic louvres, 101, 102 Acoustic modeltesting, 66 Acoustic plaster, 52 Acoustical parameters, 118 Air-handlingunits, 91, 93, 104 Mr space, 48 Aircraft flight path, 22 Aircraft frequency spectra, 21 Aircraft noise, 11, 19, 21 Albert Hall, seeRoyal Albert Hall Ambient noise level, 120 American National Standards Institute, 154 American Societyfor Testingand MaterialsStandards (ASTMS), 154—5 American Societyof Heating, Refrigeration and Mr-Conditioning Engineers (ASHRAE), 87, 91, 92, 107 Amsterdam,Concertgebauw,57 Anechoic chambers, 53, 107 Annoyance, 78 Appraisals:

environmental, 7, 31 Articulation index, 128, 144 ArupAcoustics,54, 59 Assessment procedure: industrial noise, 28 Association ofNoise Consultants (ANC), 7, 109 Atkins,W. 5., 14 Atria, 75 Attenuation, 16, 22, 96 cross talk, 96 definition, 133 train noise, 18 Attenuators, 94, 100, 101, 107 Audience, 52 Audio Frequency Induction Loop System (AFILS), 125, 131 Auditoria modelling, 54 Auditorium ventilation, 100 Auralization, 54, 56 Authorities, regulatory, 3 Average sound insulation index ratingRw, 38 Axial fan, 92, 104 Background noise levels, 10, 26, 33, 45, 78, 88, 108, 116, 140 Balconyfronts, 81 Band limitfrequencies, 138 Banners, side wall absorbers,65 Barrier attenuation, 15 Barriers, 23 Bass traps, 52 BBC, 80 BDPAcoustics,55, 56 Belfast, Waterfront Hall, 58, 60, 61 Beranek and Ver, 5

Berlin Philharmonic, 58, 62, 64 Bestpractical means, 33 Blockwork, 39, 43 Boilers,92, 102 Brickwork, 43, 45 BridgewaterHail, Manchester,54, 58, 59 British Gypsum,43, 44, 45, 47, 56 British Standards, 157—9 British Standards Institution, 107 Broadcasting,64, 67 Broadcastingauthorities criteria, 88 Builder's work enclosure, 102 Builder's work penetrations, 97, 99, 102 Building control, 3 Building damage, 29, 30, 89 Building regulations, 3, 5, 24, 37, 48, 70 Building services, 26 Building vibration: humanresponse, 31 Cable routes, 115 Calculation ofrailway noise (Dept ofTransport), 18 Calculation ofroadtraffic noise (CORTN),14 Calibrator, 12 Cardiff, St David'sHall, 61 Cavitywalls, 41 Ceiling panels, soundreflecting, 72 Ceiling reflectors, 65 Ceiling tiles, 52 Ceiling voids, 43 Ceilings, 43, 51 suspended, 43, 44 Centralized plant, 98 Channel tunnel, 10 Chartered Institute ofBuilding ServicesEngineers (CIBSE),87, 91, 92,

94, 109

Cinemas,28, 56, 57 Cladding:

ductsand pipes, 40, 101

Clarity, 61

ClarityindexC50, 64 ClarityindexC80, 64 Clay pigeon shooting, 28, 29 Clubs, 28, 33 Coincidence, 35, 42, 48 Commissioning:4 sound systems, 116 Commissioningtests, 108 Compositeconstruction, 35, 42 Compression,119 Compressors,104, 105 Computer-aided theatre technique Computer rooms, 78 Concert halls, 30, 57—68 shape, 57 Concertgebauw,Amsterdam, 57 Condenser units, 91, 99 Conference rooms, 72, 73 Construction noise, 11, 13, 23—6 prediction of, 24 Construction plant noise, 23 Contours, 16 Control ofPollution Act, 23, 24 Conversions,57 Cooling towers, 91 Council chambers, 67, 72 Courtorder, 33 Cross-talk, 97, 93 Curtains, 51 Curtains, acoustic, 102 Damping, 89 Damping, edge, 48 Daytime, 10

'Deafaid loop systems, 125

(CAn),54

162

Index

Decibel, 134 Density, 42, 43 Department ofthe Environment, 23, 29 circular 1/85, 27 Department ofTransport, 17, 18, 20 Design acoustics, 5, 35—84 Design and build, 86 Design discipline, 4 Design stages, 2, 4 Deutlichkeit,64 Diesel engine noise, 23 Diffusion,54, 61 DIN (standards), 152 Directed sound,64 Directivity, 36, 38

factor, 134 index, 134

Discontinuity, 42

Discotheques,28, 29, 68 Docklands Light Railway, 17 Doors, 40, 45, 46 sliding,46 Doorsets, acoustics, 99 Double glazing,39 Double leaf, 40, 41 Dryconstruction, 41 Drylining, 45, 69 Ducts:

noise break-out,64, 96 regenerated noise, 96 riser, 97 shape, 97

systems, 42, 95, 133 velocities,96 Dwellings, 14 Dynamic range, 64

Early decay time, 61, 143 Early lateral energy traction, 63 Echoes, 116, 117, 126 Education buildings,69 Electroacoustics,81, 82, 110 Electroacousticssystems, 118 Electro-acousticsimulators for engineers (EASE), 54 Emissionlimits, 88 Enclosures,102, 103 Envelopment, 63 Environmental: acoustics, 5 assessments,

7, 31, 32 healthdepartment, 9, 33 officer,33, 88 noise, 1, 5 measures, 137 standards, 148 Protection Act, 26, 27, 28, 33 statement, 7, 31, 32 Equalization,120 Equipment, 11, 26, 104, 105,106 electrical, 85 locations and housing, 115 mechanical services, 190 rack, 124 refrigeration, 12, 92, 104 selection, 12 signal processing, 120 Equivalentcontinuous soundlevel, 139 Escalators,

94, 102

European BroadcastingUnion, 79, 88 Evening, 10 Facilities, airflow testing, 107 Fan coil units,99

Fan noise, calculation of, 90, 94, 95

Fan testing, 107 Fans:

axial, 92, 104 centrifugal, 92 Filter, octave band, 137 Finishes, 54 floor, 52

hard, 51 flanking: path, 35, 36 transmission, 141

flight path, 22 floors,40, 48

floating, 48, 50, 70 timber, 47, 48, 49, 50 Footfall, 89 noise, 64 Free-field measurements,9 French standards, 155—7 Frequency, 132 hand limit, 138 bands, 136 natural, 89, 90 range, 50 response, 64, 116, 117, 121, 126 spectra, 11, 12, 16, 20 aircraft, 21 fan noise, 91 train,00 Gas turbines, 93 Generators, 89, 92 German national standards, 152 Glass fibre, 51, 52 Glyndebourne Opera House, 66 Groundbournevibration,29 Halcrow Fox, 14 Hail shape, 57 Hangers, 106 Health buildings,69 Hearing: loss, 71, 132 risk, 68 Hclmholz resonators, 52 Hertz, 132 HFA noise (computer program), 14 Hospitals, 69 Hotels, 69 Hoursofoperation, 24, 28 Housing, 69

Ice rinks, 79, 110

Impact sound, 48, 107, 146 Impulsivevibration excitation,31 Independentlining, 43 Industrial buildings, 71 Industrial noise, 11, 32 assessmentprocedure, 28 Inertiablock, 105, 106 Insertion loss, 96 Institute ofAcoustics, 7 Instrumentation, standards for, 149 Insulation, 48 Intelligibility,73 speech, 82 International Organization for Standardization (ISO), 107 International standards, 150—7 Intensity level, 134 Inverse square law, 117

IR systems, 125 Isolation, 48 Isolators, 106

Index

Jordan Akustik,

57

LAb, 11, 13 LA90, 11, 26 LAeq, 11, 13, 20, 21, 26, 29

IAmax, 11 Laboratories,89 Laboratory tests, 107 Lamination, 48 Land Compensation Act, 13 Landfillsites, 27 Lateral efficiency, 59, 61 Law courts, 64, 67, 68 Lecture theatres, 67 Lecture rooms, 72 Legislation,2, 3, 17, 23, 26 Leisure noise, 28 Libraries,73 Lifts, 94, 102 Lighting, 94 LinkOping ConcertHaIl, 66

Local authority, 24, 26 Locomotives, 19, 20 Loudness, 116 Loudspeaker(s): coverage,121 line losses, 125 re-entrant horn, 121 signal distribution, 123 Louvres,acoustic,101, 102

Manchester,BridgewaterHall, 54, 58, 59 Masonry, 39, 41, 45 Mass, 43 Mass law, 35, 38, 41

Measurement: free-field,9 locations,9, 12 percentage alcons, 129 sound system intelligibility, 126 units, 11, 20, 23 vibration, 9, 11 Measurements,56 Mechanicalservices, standards, 149 Meeting rooms, 67 Metalfabrication, 26 Microphone, 10, 118, 119 height, 9 MIDAS, 59 Mineral extraction, 26, 27, 31 Mineral wool, 52 MinistryofDefence, 20 Model, physical, 54, 61 Monitoring, 10 vibration, 10 Mounts,antivibration, 104, 106 Multiplex cinemas,56, 57, 67 Multi-use, 64, 67 Museums, 73 Music noise, 29 Music practice rooms, 73, 74, 76, 77 Musicians, 64 Musikvereinsaal, Vienna, 57 National MeasurementAccreditation Service (NAMAS), 11, 46 Newdevelopments, 30 Night clubs, 28, 33 Night-time,10 NNI, see Noise and Number Index Noise:

abatement notice, 27, 33

Act 1996,

2

AdvisoryCouncil, 16, 29 air conditioning, 87

163

aircraft, 11, 19, 21 and NumberIndex (NNI), 20, 21, 140 and Statutory Nuisance Act, 26 at Work Regulations, 2 barriers, 22 break-in, 60 break-out, 38

duct, 64 climate,external, 38 construction, 11, 13, 23—6 control, 26, 28, 85 building services, 100, 101 criterion (NC), 87, 145 definition, 132 diesel engine, 23 exposure categories, 13, 18, 20 external, 88 fan, 90, 94 footfall, 64 industrial, 11, 32 assessmentprocedure, 28 insulation regulations, 13 Insulation (Railways and OtherGuided Transport Systems) Regulations1995, 17 intermittent, 89 levels:

averaging,133 boilerroom, 93 plant, 23 rail, 11, 17, 19 rail, calculation of, 18 ratingnumber (NR), 50, 145 ratings, 69, 87 regenerated, 94, 96 sensing, 120 services,5, 85—109 traffic, 12, 13, 14, 15 traffic, calculation (CORTN), 14 transportation,12 control of, 22 Norris—Eyring equation, 53, 143 Octave band, 137 Odense concerthall, 57 ODEON,54, 55, 59 Offices, 18, 75, 78, 89 open plan,77 Opera houses, 67, 80, 83 Orchestras, 52, 64, 68 pits, 67 Organization for Economic Co-operation and Development (OECD), 12

Overhead reflectors,61 Overhead soundabsorbers, 53

Panels, 51 Partitions, 35, 43 folding, 43 stud, 39 Pascal, 132 Pathdifference, 15, 22 Percentage alcons, 129, 131 Peutz and Associates BV, 56 Physical model, 54, 61 Piling, 23 Pistonphone, 12 Planning conditions, 27, 32 Planning permission,3, 13, 18 Plant: air-eonditioning,85 external, 99, 103 mobile, 25 noise, 23 stationary,25

164

Index

Plant rooms, 85, 99 absorption, 99 structure, 99 Plaster,acoustic,52 Plenum chambers, 98 Pop concerts, 29 Power amplifiers,120 Power train noise, 12 Pre-amplifsers, 19

Prediction: construction site noise, 24, 25 PreferredNoise Criterion (PNC), 145 Priorconsent, 24 Privacy, 69, 77, 78 Publications:reference, 3 Pumps, 104, 105 Pure tone audiometry, 71

Separation, 36 Servicepenetrations, 93, 99 Services:

noise, 5, 85—109 advice timing, 86 design criteria, 87 piped,85 Sheetmaterials, 39 Shopping malls,53 Signal:

direct-to-reverberant, 127 distribution, 123 Signal-to-noise ratio, 116, 117, 127 Silencers,28, 93, 96 Silencing,85 Single event roadvehicle noise, 16 Single glazing, 39 Site:

Quadratic residue sequence, 64 Quilt, 40

Radio facilities, 79 Rail noise, 11, 17, 19 attenuation, 18 Railway Noise Insulation Regulations, 17 Rapid Speech TransmissionIndex (RASTI), 54, 128, 130,131 definition, 145 Ratio of early to late energy, 63 Ratio of early to reverberant energy, 59 Real timeanalyser, 12 Recording, 64 Recording studios, 79 Reflection,54 Refrigeration equipment, 12, 92, 104 Regenerated noise, 94, 96 Regulatory authorities, 4 Renton Howard Wood Levin,59 Resilience, 104 Re-radiation, 42 Resonances,52, 104 partition, 35, 42 Resonant frequency, 40 definition, 146 Reverberation, 116, 117, 127 time, 52, 53, 59, 64, 67, 68, 77, 79, 120, 140 Riser ducts, 97 Roadnoise, 11, 12, 13, 14, 15, 22 computerprogram, 14 Robinson and Mcllwaine, 61 Rolling noise, 12 Roofs, 42 flat,43 lightweight,43 Room(s): acoustics, 36, 38, 54 radius, 144 reverberation, 107

units, 98 Royal Albert Hall London, 54, 63

St. David's Hall, Cardiff, 61

Sabine equation, 53, 144 Sabine RT, 61, 63 Sample periods, 12 Sandy Brown Associates, 60 Schools, 69

Screens, 102, 103 SEL (Sound exposure level), 11, 17, 20 Seating, 58, 64 vineyard,58, 62 Seats, 52, 65 SegestromHall, California,58, 66 Separating walls, 57, 70

boundary, 85 survey, 8, 12 Slant distance, 22 Sound, 1, 132 absorbers,overhead, 53 absorption, 48 coefficient,144 Attenuators Ltd, 48, 50 decay analysis, 55 exposure level, 17, 140 insulation, 35, 48, 140 standards for, 149 leaks, 42 level difference, 35, 37, 141 standardized, 142 power:

level, 136 measurement, standards for, 148 pressure level, 118, 133,135 maximum, 139 octave band, 137 peak, 140 reverberant, 53, 143 reduction index (SRI), 37, 39, 40, 140 composite construction, 142 reinforcement systems, 59, 110—13 standards for, 148 Research Laboratories,5, 68, 91 systemintelligibilitymeasurement, 126 systems, 5, 110—31 design checklist, 114 input requirements, 115 quality, 114 transmission class, 141 coefficient, 141 Spatial impression,63 Speech intelligibility, 82, 125 interference level, 145 privacy, 45, 88, 128 reinforcement, 68

transmission index, 146 transmission tests, 130 Sports stadia, 110 Standardized soundlevel difference DnT, 142 Standards, 148—59 American, 154—5 British, 157—69 French, 155—7 German, 152—4 International, 150—7 Standby diesels, 105 Static deflection, 90, 104, 106 Statutes, 3 Stiffness,35, 42, 48 Structureborne noise, 23, 25, 30, 89, 142 Studios, 30, 43, 52 modular, 80 production, 46 recording, 79

Index

commissioning,108 laboratory, 107 works, 107 Theatres, 67, 69, 80 Timber Research and DevelopmentAssociation (TRAI)A), 49 Trading rooms, 83

Ventilation noise, 57, 69, 94 Ventilation openings, 99 Vibration, 5, 85—109, 147 acceptable levels, 29 groundborne, 29 Vibration isolation,90, 93, 102, 104, 105, 106 Vibration levels, 30 Vibration measurement, 9, 11 standards for, 149 Vibration monitoring, 10 Vibration transmission,89, 93 Video conferencing, 73 Vienna, Musikvereinsaal, 57 Vineyard seating, 58, 62 Voids, ceiling, 43 Volume,58

noise, 12, 13, 14, 15 speed, 15 Trains, frequency spectra, 20

Walls, 43 Water-skiing, 29

Surfaces,reflecting, 72

Survey procedure, 9 Swimmingpools, 79, 110 Technical information, 132—59 Televisionfacilities,79 Temperature inversions, 11 Ten-pin bowling, 28, 33 Tests:

Traffic:

se€ also Rail

Units, measurements, 11, 13, 17, 20, 23, 28, 29

Waterfront Hall, Belfast, 58, 60, 61 Weather, 10, 11, 12 Weighted normalized impact soundlevel, 147 Weighted sound reduction indexRw, 142 Weighted standardized level difference (D,,T), 37, 143 Weightingnetworks, 136 specthcation, 137 Wellington TownHall, New Zealand, 63 Windfarms, 32 Windows,48, 69 Winds, 10 Wiring, 124 WycombeEntertainments Centre, 66

Valves, 94 Velocity, 29

Young's modulus, 42

Transfer grilles,97 Transformers, 105 Transmission:

flanking, 141 loss, 141 path, suites, 107 Transportation noise, controlof, 22 Treatments, 51

Ventilation,64, 108 auditorium, 100 natural, 2, 14, 75

Zoning, 78

165

ARCHITECTURE ACOUSTICS

Acoustics in the Built Environment is an invaluable work of reference for the building professional,covering all aspects

of acoustics. It is unique in its range of topics: the

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of current legislation for this second edition. The book presents information relevant to the day-to-day

work of project

design teams

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documents,which can be cited in performancespecifications.

Its broad range

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its ease of use make

Acoustics in the Built Environment an indispensable source of information acoustics,

for anyone

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whether they are architects, planners, engineers

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A qualified acoustician and architect of long experiences Duncan Templeton has co-written three other books on

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