Acoustics Dissertation

DISSERTATION ON “ARCHITECTURAL ACOUSTICS AND ITS

TREATMENT”

Submitted by: SAIF SIDDIQUI 091110025

Under the guidance of Dr. ANUPAMA SHARMA

DEPARTMENT OF ARCHITECTURE AND PLANNING Maulana Azad National Institute of Technology, Bhopal

APRIL 2013

MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY, BHOPAL DEPARTMENT OF ARCHITECTURE AND PLANNING

DECLARATION

This Dissertation in subject AR 494, entitled “ARCHITECTURAL ACOUSTICS AND ITS TREATMENT”  is being submitted as part of requirement for eighth

semester of Bachelor of Architecture by the undersigned for evaluation. The matter embodied in this dissertation is either my own work or compilation of others’ work, acknowledged properly. If, in future, it is found that the above statement

is false, then I have no objection in withdrawal of my Dissertation and any other action taken by the Institute.

Date: SAIF SIDDIQUI 091110025

1

APRIL 2013

MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY, BHOPAL DEPARTMENT OF ARCHITECTURE AND PLANNING

DECLARATION

This Dissertation in subject AR 494, entitled “ARCHITECTURAL ACOUSTICS AND ITS TREATMENT”  is being submitted as part of requirement for eighth

semester of Bachelor of Architecture by the undersigned for evaluation. The matter embodied in this dissertation is either my own work or compilation of others’ work, acknowledged properly. If, in future, it is found that the above statement

is false, then I have no objection in withdrawal of my Dissertation and any other action taken by the Institute.

Date: SAIF SIDDIQUI 091110025

1

MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY, BHOPAL

DEPARTMENT OF ARCHITECTURE AND PLANNING

CERTIFICATE

This is to certify that the Dissertation entitle “ARCHITECTURAL ACOUSTICS AND ITS TREATMENT” is a piece of research work done by Saif Siddiqui  under my guidance and supervision and to the best of my

knowledge and belief that this dissertation is:

(i)

Embodies the work of the candidate himself;

(ii)

has duly been completed;

(iii)

Up to the standard both in respect of contents and language for

 being  bein g referred ref erred to the th e examiner exa miner..

Recommended

Dr. Anupama Sharma Associate Professor, Department of Architecture and Planning MANIT, Bhopal. Date

2

ACKNOWLEDGEMENT

I deemed it my privilege to extend my profound gratitude and appreciation to all those who have directly or indirectly involved themselves in helping me to proceed with the Dissertation work. My sincere appreciation and thanks to Supervisor/guide Dr. Anupama Sharma for their diligent attention towards the dissertation throughout all stages of work. Their comments and criticism have been invaluable. I am thankful to all faculty members for their inspiration, without which it was impossible to finish the task. The writing of this dissertation has been one of the most significant academic challenges I have ever taken. Though the following dissertation is an individual work, I could never have reached the heights or explored the depths without the help of  books published by various authors, the e-books available on the internet and websites  providing information related to my dissertation topic.

SAIF SIDDIQUI 091110025

3

Table of Content Declaration .................................................................Error! Bookmark not defined.  Acknowledgement ......................................................Error! Bookmark not defined. Table of Content .................................................................................................... 4 Chapter-1.

Synopsis .......................................................................................... 7 

1.1

Title ................................................................................................................. 7

1.2

Needs and Concerns......................................................................................... 8

1.3

Aim ................................................................................................................. 8

1.4

Objectives........................................................................................................ 8

1.5

Scope ..............................................................................................................8

Chapter-2.

Introduction .................................................................................... 9 Error! Bookmark not defined.

2.1

Acoustics ...............................................................

2.2

History of Acoustics ....................................................................................... 10

2.3

Sound and its Mechanism .............................................................................. 16

2.4

Noise .....................................................................

Chapter-3.

Error! Bookmark not defined.

 Acoustical Treatment Of Various Spaces ........................................ 35

3.1

Classrooms .................................................................................................... 35

3.2

Concert Hall ................................................................................................... 36

3.3

Office ............................................................................................................ 38

3.4

Studio ............................................................................................................ 39

3.4

Theatre.......................................................................................................... 40

Chapter-4.

 Acoustic Materials ........................................................................ 41

Chapter-5.

 Acoustical Treatments................................................................... 42

5.1 Common Construction Materials .......................................................................... 42

4

5.2

Specialtiy Construction Materials ................................................................... 44

5.3

Floors ............................................................................................................ 46

5.4

Stringers ........................................................................................................ 4 9

5.2

Ceilings .......................................................................................................... 50

5.3

Walls ............................................................................................................. 52

5.4

Doors ............................................................................................................ 54

5.5

Windows ....................................................................................................... 5 7

Chapter-6.

Conclusion .................................................................................... 60 

Chapter-7. References ......................................................................................... 60 

5

6

Chapter-1. Synopsis 1.1 Title Architectural Acoustics And Its Treatment

1.2 Introduction Architectural acoustics refers to the control of sound and vibrations within buildings. Although architectural acoustics was first applied to opera houses and concert halls, this branch of acoustical engineering applies to any enclosed area, whether concert halls, office spaces, or ventilation ducts. The acoustics of rooms are often considered to ensure speech intelligibility and  privacy. One thing that can affect speech intelligibility is standing waves. A standing wave results from a sound wave reflected 180 degrees out of phase with its incident wave, which often occurs for at least one specific frequency when two walls are  placed parallel to each other. To avoid this, many rooms are designed with angled walls. A second potential cause of poor speech intelligibility is reverberation.  This effect can be reduced through porous absorbing materials. Examples of these include glass or mineral fibers, textiles, and polyurethane cell foams. Since the absorption of each material is different for different frequencies of sound, the materials used often vary based on the intended purpose of the room, though compound partitions, or layered combinations of different materials, make more effective absorbers. A third common technique for room acoustics is the use of masking. Masking is the canceling or drowning out of other sounds. Although this raises the overall sound pressure, masking can make irritating noises less distracting and add speech privacy As these examples highlight, room acoustics are a regular part of architectural design. Reducing ventilation noise serves as another example of applied architectural acoustics. Many heating, ventilation, and air conditioning systems have silencers. Silencers can actively cancel noise by electronic feed forward and feedback techniques, or muffle the sound by either having sudden changes in cross section or walls with absorbent linings.Architectural acoustics involves the control of sound for ventilation, rooms, and anything else indoors. .

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1.3 Needs and Concerns In today’s architectural environment, good acoustical design isn’t a luxury –  it’s a necessity. Acoustics impacts everything from employee productivity in office settings to performance quality in auditoriums to the market value of apartments, condominiums and single-family homes. While the science behind sound is well understood, using that science to create desired acoustical performance within a specific building or room is complex. There’s no single acoustical “solution” that can

 be universally applied to building design. Each built environment offers its own unique set of acoustical parameters. The acoustical design for a business conference room, for instance, differs greatly from the design needed for a kindergarten classroom. Understanding these differences and knowing how to utilize building materials, system design and technologies are key factors behind successful acoustical design. This research will provide basic background on the science and measurement of sound, as well as insights into some of the principles of architectural acoustical design.

1.4 Aim To study the architectural acoustical designing of spaces.

1.5 Objectives 

To study the sound and its mechanism



Study acoustics of an enclosure..



To study treatment of moise..

1.6 Scope Since this is an architectural report, the literature study will cover study of acoustics in an architectural space. This research will provide basic background on Introduction to sound, as well as insights into acoustical designing of spaces  principles and noise reduction techniques.

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1.7 Methodology 

Literature survey 1. Basics of acoustics 2. Various acoustical treatments 3. Relevant case studies.



study of the acoustical materials for treatments



acoustical measures for respective enclosures.

Chapter-2. Introduction 2.1 Acoustics Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical or audio engineer. The application of acoustics can be seen in almost all aspects of modern society with the most obvious being the audio and noise control industries.

The word "acoustic" is derived from the Greek word ακουστικός (akoustikos), meaning "of or for hearing, ready to hear" and that from ἀκουστός (akoustos), "heard, audible", which in turn derives from the verb ἀκούω (akouo), "I hear". The Latin synonym is "sonic", after which the term sonics used to be a synonym for acoustics and later a branch of acoustics. Frequencies above and below the audible range are called "ultrasonic" and "infrasonic", respectively.

Figure 3.1 Auditorium Stravinski, Montreux

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The acoustical environment of a workspace is typically given little or no attention during project planning and design. The functionality and aesthetics of the workspace are usually the primary focus of the designer. Too often overlooked, are the factors contributing to the productivity of employees occupying the workspace. Providing a comfortable environment for employees contributes significantly to their optimum  performance and reduced absenteeism. Workspace comfort is really a combination of factors that includes day lighting and electric lighting, indoor environmental quality, temperature, and acoustics. The assault on ears in the workplace can come from traffic noise outside, mechanical equipment in adjacent spaces, and copiers, phones, and voices within the workspace.

2.2 History of Acoustics The historical development of architectural acoustics is similar to other fields of  building design, in comprising two parallel strands of ideas  –   the science and mathematics of the subject on the one hand, leading to improved understanding of the  phenomena, and the methods used by designers when faced with the challenge of a new building on the other, especially when the task differs markedly from precedent. The two nineteenth-century classic works on the physics of acoustics (Helmholz 1863; Strutt 1877-78) hardly mentioned the acoustics of theatres or other rooms, and the science they contained only began to be used by architectural acousticians in the mid-twentieth century. While these two branches of knowledge are closely related, it was not a case of theory leading to practice, or vice versa: the two were symbiotic.

2.2.1 Acoustics in The Ancient World Vitruvius on acoustics and theatre design

The Roman engineer Vitruvius devoted several chapters of his book on building design and construction to the location and design of theatres (Vitruvius, Book V). He advised that they should be located away from winds and from “marshy districts and other unwholesome quarters” and also on their orientation with respect to the sun and

the surrounding terrain. He addressed key geometric issues such as the plan and section, sight lines, numbers and locations of entrances and exits, and finally considered the subject of acoustics. This highly theoretical section was not his own; he was repeating what he found in various Greek treatises on acoustics from two or

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three centuries earlier which, in turn, probably had their origins in Pythagoras who first developed the subject around 530 BC. Vitruvius dealt with acoustics from several  points of view. First he introduced harmonics –  “an  obscure and difficult branch of musical science, especially for those who do not know Greek”. This science explained

the pitch of notes and the intervals between them in the Greek musical scale, as well as why some combinations of notes are concordant and others discordant. Next Vitruvius discussed sound in the auditorium –   in particular the need for sound of all  pitches to travel from the stage to the ears of every member of the audience by a direct route, in the manner of waves created by a pebble thrown into water. This led logically to both raked seating and the semi-circular plan. He advised against vertical reflective surfaces that would prevent sound reaching the upper tiers of seats since this particularly impairs the intelligibility of word endings which, in Greek and Latin, are vital to comprehension. Such reflected waves, he wrote, can also interfere with the direct waves and distort sounds for the listener. These explanations differ remarkably little from how we would put it today. Thirdly, Vitruvius explained that the site of a theatre itself must be carefully selected taking account of acoustics: it must not have an echo, nor give reflections that can lead to direct (incident) and reflected sounds interfering. Vitruvius also discusses the use of sounding vessels  –   nowadays called Helmholz resonators, after the nineteenth-century German physicist who explained how they function  –   which, he says, reinforce certain frequencies of the human voice and can increase intelligibility. These open-ended vessels were made of bronze and tuned to six notes of the chromatic scale. Two sets of six were arranged beneath a tier of seats symmetrically either side of the centre line of the theatre. If the theatre were  particularly large, two additional sets of vessels should be installed in higher rows, each a few semi tones lower in pitch  –   a total of thirty six different notes. Vitruvius admits he knows of no theatres that had actually been built in Rome with sounding vessels. The reason, he explains, is that “the many theatres that are constructed in

Rome every year contain a good deal of wood which does not lead to the same  problems with reflections as stone”. Also, he says, the timber panels themselves can

resonate in a manner similar to the air in a sounding vessel and so improve intelligibility. As to the effectiveness of sounding vessels, they are known today not to improve intelligibility and that is probably why they were not used in Rome. Whether

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the Roman theatres were as good as the Greek ones, we do not know, but there is no doubt that both were designed with great understanding of acoustics and expertise in using this understanding to achieve demonstrably better results. One final recommendation from Vitruvius on acoustics was for a senate house. The height of a senate house should be half the width of the building, he says, and coronae, or cornices, made of woodwork or stucco, should be fixed half way up the inside faces of the walls around the entire room. Without these, he says, the voices of men engaged in discourse are lost in the high roof. With coronae, the sound of the voices is ‘detained before rising’ and so is more intelligible to the ear. Acoustics In The Mediaeval And Renaissance Eras

 No significant writings on the acoustics of buildings survive from mediaeval or Renaissance times (Hunt 1978). Vitruvius was published in the late 15th century and would have been known by most designers of large buildings. However, it is not  possible to identify precise ways in which his guidance was followed, either in cathedrals or, from the late Renaissance, in theatres. The development of music from the 12th century provides evidence of a good understanding of the acoustics of cathedrals; however, their legendary acoustic qualities are more indebted to the skill of composers and musicians than to the buildings themselves or their designers. They have long reverberation times because sound waves are reflected many times with little loss of intensity which means that musical rhythms have to be slow to be intelligible, and percussive instruments must not be used to avoid the inevitable machinegun effect of any echo. The acoustic of the space favours those instruments with a gradual attack to each note, and which sustain their notes –   for example the organ, flute, violin and the human voice. For speech, however, the long reverberation time is a disaster. As the distance between speaker and listener increases, so the sound reaching the ear directly is increasingly swamped by the reflected sounds arriving by indirect, longer sound paths. Speech is thus generally unintelligible at any distance greater than a few meters, which phenomenon has an interesting architectural effect. Since it is the longer wavelengths of lower notes that are more effectively reflected,  people talking in cathedrals are naturally and unconsciously inclined to whisper, irrespective of any reverence for the religious nature of the buildings they may feel,  because whispering removes the lower frequencies of the human voice.

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Early Modern Design Guidance –  Eighteenth Century

As in the ancient world of building described by Vitruvius, it was the intelligibility of speech that drew the attention of 17th and 18th century building designers to the acoustic performance of building interiors, especially in two types of building  –  theatres and the debating chambers used by politicians. During the eighteenth century the importance of room acoustics was further heightened with the invention of a number of musical instruments such as the harpsichord and fortepiano, and the growing popularity, in elite circles at least, of chamber music. The new instruments used ingenious mechanisms and large sounding boards to produce plucked and  percussive notes with unprecedented speed and at much greater volumes than earlier instruments such as the lute, harp and clavichord. When played in a room with a very live acoustic, the individual notes became indistinguishable and the objectives of the instrument makers and musicians were ruined. Throughout Europe the second half of the eighteenth century saw a boom in theatre  building in the major cities, and designers generally learned from the acoustic disasters of the early century. By the late eighteenth century it was common practice to use the ceiling or soffit above the front of the stage as a ‘sounding board’ (actually a reflector) and the ceiling over the orchestra pit to ‘throw the voice forward’ from the

stage to the back of the stalls and to the galleries. The first design guides for theatres discussed acoustics alongside the equally important issue of line-of-sight (Patte 1782, Saunders 1790, Rhode 1800, Langhans 1810). These and others followed Patte’s

example

in

showing

ray

diagrams

to

visualise

sound

paths.

Fig. 3.2 Ray diagrams for different theatre plans; (Patte 1782, Plate 1)

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Wallace Clement Sabine – “Father Of Architectural Acoustics”

The man who has no rival in being called “the father of architectural acoustics” was

Wallace Clement Sabine (1868-1919) (Sabine 1922; Beyer 1999, pp.186-191; Thompson 1992, 2002). Sabine was a lecturer in physics in the department of natural  philosophy at Harvard University and was approached in 1895 to advise on how to improve the poor acoustics of a new lecture theatre in the University’s Fogg Art Museum. This lecture theatre had been designed to emulate a classical Greek theatre and followed the same principles of acoustic design that Vitruvius had written down. These addressed the need of intelligibility by focusing mainly on maintaining the volume of the direct sound that reached the listener’s ear. The speaker was placed

above the level of the front row of the audience; the seating was raked upwards towards back of the auditorium; and a wall was placed behind the speaker to reflect sound into the auditorium. However, such principles were intended for open-air theatres and took no account of sound reflected from walls or the roof. In an enclosed room these reflected sounds also reach the listener’s ear and, since there will be many sounds, arriving at different times, the result is confusion with direct sound from a speaker competing with reflections of earlier sounds. Sabine realised this was how intelligibility was lost, like many before him. Being a physicist, however, his approach was to conduct experiments to measure how the loudness of the reflections was influenced by the reflecting surfaces in the lecture theatre. His aim was to discover the relationship between the dimensions of the room and the rate at which a sound became quieter and eventually became inaudible. He called this rate of decay the reverberation time and defined it as the time, in seconds, for a sound to decay to one millionth of its original loudness (a fall of 60dB). Sabine had to work at night to ensure all extraneous sounds were avoided. He used a single organ pipe with a frequency of 512 Herz (an octave above middle C). In 1895 there were no microphones or audio-electronics Proceedings of the Third International Congress on Construction History, May 2009 and the judgement as to when the sound was inaudible was made by the experimenter himself. An electric chronograph recorded the times to one-hundredth of a second. By covering more and more of the auditorium’s wooden se ats with soft cushions, he showed that the reverberation time

was inversely proportional to the number of seats covered with cushions. He repeated the experiments in eleven other rooms in the university, with volumes ranging from a

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lecture theatre of 9300 cubic metres down to an office of just 35 cubic metres. From the results he derived the equation for which his name is well-known giving the relationship between the reverberation time (RT), of a room, in seconds, its volume (V), in cubic metres, and the area (A), in square metres, of sound-absorbing surfaces in the room. (1) Sabine used this equation to give an objective means of comparing different auditoria and, in particular, to compare the proposed design for the new Boston Music Hall with the Leipzig Gewandhaus, on which its overall shape was  based, and the old Music Hall in Boston. He was able to specify, for the first time, the  precise degree of sound absorption in the interior of the new Boston hall needed to achieve the same reverberation time as the Leipzig Gewandhaus whose seating capacity it exceeded by 70%, and volume by 40%. Sabine’s predictions were accurate

and the acoustic of the new hall was widely praised. He had fulfilled his goal of overcoming the “unwarranted mysticism” that then surrou nded the subject of architectural acoustics and, most importantly, achieved “the calculation of reverberation in advance of construction”. Sabine was soon being approached by the

owners of various types of room to advise on how to rectify their acoustic problems. Often this followed the failed attempts by others to deal with the problems. Sabine noted the persistent use of a traditional but wholly ineffective remedy which involved stretching a grid of steel wires in the top of a church, theatre or court room which suffered too much reverberation on the mistaken believe that the wires would resonate and absorb sound. In New York and Boston he had seen theatres and churches with  just four or five wires stretched across the room while in other auditoria several miles of wire had been used, all without the slightest effect. As part of his diagnosis of acoustic problems he would sometimes plot a contour map showing the distribution of the sound intensity. This helped him identify the source of the worst sound reflections from the walls and ceiling and hence reduce them by using sound-absorbing panels or adding decorations that would break up strong reflections from large plane surfaces. Sabine also turned his attention to the design of new theatres and how best to create a near-uniform acoustic experience for every member of the audience. To help him in these studies he used the newly-perfected schlieren method of photography to show sound waves passing through air in twodimensional models of auditoria (Fig.2). He was thus able to show in plan and

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section, how sound waves were reflected and broken up as they emanated from the stage into the auditorium. Outside the field of building structures this was probably the first use of a scale model to investigate the engineering behaviour of a building.

Fig 3.3 Photographs showing the progress of sound waves through a model of a theatre.

The development of design methods for the acoustics of auditoria has followed the same pattern observed in other branches of building engineering design. Initially designers used their own experience to observe and improve their art and collected their experience in the form of simple design rules which could be passed on to other designers. In acoustics this approach was known in ancient times and has continued even into the twentieth century. The technical difficulty of measuring acoustic  phenomena delayed a truly scientific approach to understanding acoustics until the late eighteenth century (over a century later than for structural engineering). The first scientific concept in acoustics, defined in quantitative terms by Sabine in the 1890s, was the reverberation time whose relationship to the dimensions of a room was expressed as an empirical quantity known as the absorptivity of the surfaces of the room. This approach remains the most important in acoustic design today. The testing of scale models together with the use of non-dimensional constants was developed in acoustics simultaneously with their use in the design of building structures, first in the 1930s and more widely in the 1960s. Their use consolidated the understanding of acoustic phenomena and laid the foundation for creating mathematical models using computers.

2.3

Sound and its Mechanism

Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing. Sound also travels through plasma

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2.3.1

Propagation of sound

Sound is a sequence of waves of pressure that propagates through compressible media such as air or water. (Sound can propagate through solids as well, but there are additional modes of propagation). Sound that is perceptible by humans has frequencies from about 20 Hz to 20,000 Hz. In air at standard temperature and  pressure, the corresponding wavelengths of sound waves range from 17 m to 17 mm. During propagation, waves can be reflected, refracted, or attenuated by the medium.

Fig. 3.2 Travelling of sound waves

The behaviour of sound propagation is generally affected by three things: 





A relationship between density and pressure. This relationship, affected by temperature, determines the speed of sound within the medium. The propagation is also affected by the motion of the medium itself. For example, sound moving through wind. Independent of the motion of sound through the medium, if the medium is moving, the sound is further transported. The viscosity of the medium also affects the motion of sound waves. It determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible.

When sound is moving through a medium that does not have constant physical  properties, it may be refracted (either dispersed or focused).

2.3.2

Perception of Sound

The perception of sound in any organism is limited to a certain range of frequencies. For humans, hearing is normally limited to frequencies between about 20 Hzand 20,000 Hz (20 kHz),[3] although these limits are not definite. The upper limit generally decreases with age. Other  species have a different range of hearing. For example,

17

dogs can perceive vibrations higher than 20 kHz, but are deaf to anything below 40 Hz. As a signal perceived by one of the major  senses,  sound is used by many species for detecting danger, navigation, predation, and communication. Earth's atmosphere, water,

and

virtually

any physical

phenomenon,

such

as fire,

rain, wind, surf, or   earthquake,  produces (and is characterized by) its unique sounds. Many species, such as frogs, birds, marine and terrestrial mammals,  have also developed

special organs to

 produce song and speech. 

produce

sound.

In

Furthermore, humans have

some developed

species, culture

these and

technology (such as music, telephone and radio) that allows them to generate, record, transmit, and broadcast sound. The scientific study of human sound perception is known as psychoacoustics. 2.3.3

Physics of Sound

The mechanical vibrations that can be interpreted as sound are able to travel through all  forms of matter: gases, liquids, solids, and plasmas.  The matter that supports the sound is called the medium. Sound cannot travel through a vacuum. Longitudinal and transverse waves

Sound is transmitted through gases, plasma, and liquids as longitudinal waves,  also called compression waves. Through solids, however, it can be transmitted as both longitudinal waves and  transverse waves.  Longitudinal sound waves are waves of alternating pressure deviations from the equilibrium pressure, causing local regions of  compression and rarefaction,  while transverse waves (in solids) are waves of alternating shear stress at right angle to the direction of propagation. Matter in the medium is periodically displaced by a sound wave, and thus oscillates. The energy carried by the sound wave converts back and forth between the potential energy of the extra compression (in case of longitudinal waves) or lateral displacement strain (in case of transverse waves) of the matter and the kinetic energy of the oscillations of the medium. Sound wave properties and characteristics

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Figure 3.3  Sinusoidal waves of various frequencies; the bottom waves have higher frequencies than those above. The horizontal axis represents time.

Sound waves are often simplified to a description in terms of  sinusoidal plane waves, which are characterized by these generic properties: 

Frequency, or its inverse, the period



Wavelength



Wave number



Amplitude



Sound pressure



Sound intensity



Speed of sound



Direction

Sometimes speed and direction is combined as a velocity vector;  wave number and direction are combined as a wave vector. Transverse

waves, 

also

known

as shear waves,

have

the

additional

 property, polarization, and are not a characteristic of sound waves.

2.3.4 Speed of Sound The speed of sound depends on the medium the waves pass through, and is a fundamental property of the material. In general, the speed of sound is proportional to the square root of the ratio of the elastic modulus (stiffness) of the medium to its density.  Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in gases depends on temperature. In 20 °C (68 °F)  air at sea level,  the speed of sound is approximately 343 m/s (1,230 km/h; 767 mph) using the formula "v = (331 + 0.6 T) m/s". In fresh water, also at 20 °C, the speed of sound is approximately 1,482 m/s (5,335 km/h; 3,315 mph). In steel,  the speed of sound is about 5,960 m/s (21,460 km/h; 13,330 mph).[6] The speed of sound is also slightly sensitive (a second-order  anharmonic effect) to the sound amplitude, which means that there are nonlinear propagation effects, such as the production of harmonics and mixed tones not present in the original sound.

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2.3.5

Measurement of Sound

Sound is measured in dB (decibels). The decibel (dB) is a logarithmic unit that indicates the ratio of a physical quantity (usually power or  intensity)  relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to  base 10 of the ratio of two power quantities.[1] A decibel is one tenth of a bel, a seldom-used unit named in honor of  Alexander Graham Bell.

Fig. 3.4 Various sounds and their dB units.

2.3.6 Acoustic Terms Reverberation

enclosed space, when a sound source stops emitting it takes some time for the sound to become inaudible. This prolongation of the so

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room caused by continued multiple reflections is called reverberation. Re time plays a crucial role in the quality of music and the ability to understand s given space. When room surfaces are highly reflective, sound continues to reverberate. The effect of this condition is described as a live space with a long rev time. A high reverberation time will cause a build-up of the noise level in a space. of reverberation time on a given space are crucial to musical conditions and und speech. It is difficult to choose an optimum reverberation time in a multi-functio different uses require different reverberation times. A reverberation time that is op a music program could be disastrous to the intelligibility of the spoken word. Co reverberation time that is excellent for speech can cause music to sound dry and fla

Reflections

Reflected sound strikes a surface or several surfaces before receiver. These reflections can have unwanted or even consequences. Although reverberation is due to continued reflections, controlling the Reverberation Time in a space does space will be free from problems

reac

from

not r

Reflective corners or peaked ceilings can create a “megaphone” effect potentiall annoying reflections and loud spaces. Reflective parallel surfaces lend themselves t acoustical problem called standing waves, creating a “fluttering” of sound betwee surfaces.

Reflections can be attributed to the shape of the space as well as the material on th Domes and concave surfaces cause reflections to be focused rather than dispersed cause annoying sound reflections. Absorptive surface treatments can help to elim reverberation and reflection problems.

Noise Reduction Coefficient The  Noise Reduction Coefficient (NRC) is a single-number index for rating how ab  particular material is. Although the standard is often abused, it is simply the average o frequency sound absorption coefficients (250, 500, 1000 and 2000 Hertz rounded to t 5%). The NRC gives no information as to how absorptive a material is in the lo frequencies, nor does it have anything to do with the material’s barrier effect.

Sound Transmission Class (STC):

The Sound Transmission Class (STC) is a single-number rating of a material’s or assembly’s barrier effect. Higher STC values are more efficient for reducing sound transmission. For example, loud speech  be understood fairly well through an STC 30 wall but should not be audible through an STC 60 wall. The rating assesses the airborne

can

21

sound transmission performance at a range of frequencies from 125 Hertz to 4000 Hertz. This range is consistent with the frequency range of speech. The STC rating does not assess the low frequency sound transfer. Special consideration must be given to spaces where the noise transfer concern is other than speech, such as mechanical equipment or music. Even with a high STC rating, any penetration, air-gap, or “flanking” path can seriously degrade the isolation quality of a wall. Flanking paths are the means for sound to transfer from one space to another other than through the wall. Sound can flank over, under, or around a wall. Sound can also travel through common ductwork, plumbing or corridors.

2.4

Noise

Fig 3.5 graph showing noise levels

In relation to sound, noise is not necessarily random. Sounds, particularly loud ones, that disturb people or make it difficult to hear wanted sounds, are noise. For example, conversations of other people may be called noise by people not involved in any of them; any unwanted sound such as domesticated dogs barking, neighbours playing loud music,  portable mechanical saws, road traffic sounds, or a distant aircraft in quiet countryside, is called noise. Acoustic noise can be anything from quiet but annoying to loud and harmful. At one extreme users of   public transport sometimes complain about the faint and tinny sounds emanating from the headphones or  earbuds of somebody listening to a portable audio  player; at the other the sound of very loud music, a jet engine at close quarters, etc. can cause permanent irreversible hearing damage. Sound intensity follows an inverse square law with distance from the source; doubling the distance from a noise source reduces its intensity by a factor of four, or 6 dB.

22

2.4.1

Reverberation time

With this theory described, the reverberation time can be defined. It is the time for the

level of energy to decrease of 60 dB. It depends on the volume of the room V and the equivalent absorption area a :T60 =0.16V a Sabine formula This reverberation time is the fundamental parameter in room acoustics and depends trough the equivalent absorption area and the absorption coefficients on the frequency. It is used for several measurement : • Measurement of an absorption coefficient of a material • Measurement of the power of a source • Measurement of the transmission of a wall

2.4.2 Controlling Noise Controlling Noise Between Spaces

Controlling noise between spaces is frequently an issue in residential  projects and office spaces. Noise will travel between spaces at the weakest  points, such as through a door or outlet. There is no reason to spend money or effort to improve the walls until all the weak points are controlled. General rules of thumb for controlling noise between spaces: 













A wall must extend to the structural deck in order to achieve optimal isolation. Walls extending only to a dropped ceiling will result in inadequate isolation. Sound will travel through the weakest structural elements, which, many times, are the doors or electrical outlets. When the mass of a barrier is doubled, the isolation quality (or STC rating) increases by five, which is clearly noticeable. Installing insulation within a wall or floor/ceiling cavity will improve the STC rating by about 4-6 dB, which is clearly noticeable. Often times, specialty insulations do not perform any better than standard batt insulation. Metal studs perform better than wood studs. Staggering the studs or using dual studs can provide a substantial increase in isolation. Increasing air space in a wall or window assembly will improve isolation.

Case Study

23

Location: Area

of

Newspaper concern:

Space

between

office CEO

office

building and

boardroom

Additional information: Noise usually travels through spaces at several different points. Controlling only one point is like trying to save a sinking boat by patching only one hole when 10 holes exist. You must be thorough to ensure effective results. Questions to ask client:  

 

 

Please describe the problem. Does the wall go all the way up to the deck and is it sealed airtight? Does it just go up to the dropped ceiling? Are there any penetrations through the wall? Are there any penetrations through the wall? Could the noise be going around the wall? Are there any air gaps? Under the door? At the perimeter of the wall? At the window mullion? Etc? What materials are used in the space(s)? What are your confidentiality needs?

Client feedback: 

   



The CEO is distracted by noise from the boardroom when there are meetings in  progress. There are also confidentiality issues. The wall does not go up to the deck, it ends at the dropped ceiling. There are no penetrations other than the door. The noise could be going around the wall by means of the door. The materials used in this space are carpet, painted drywall and acoustic tile on the ceiling. There are two return air ducts about two feet apart, separated only by the wall. Confidentiality is an issue to some degree, but not a security problem.

Evaluation: In this particular project, there was a door and a window between the two spaces and the ceiling did not go up to the deck. To improve the acoustics, an upgraded sealer was added to the doors and a flexible, vinyl barrier was placed on top of the ceiling above the two spaces (since the wall could not be extended to the deck). Creating a completely confidential space is very difficult and extremely expensive. Since confidentiality was an issue, but not a security matter, this improvement proved successful. If further improvements were needed, the next step would be to install a sound masking

system.

Further comments: In another office space, where complete confidentiality was

24

essential, a very expensive door was installed. This door had an STC rating of 65, but the surrounding walls had an STC rating of 50. In this case, the walls served as the weakest point, rather than the door. It’s important to note that the isolation quality of

an assembly is dictated by the weakest element of the assembly.

Controlling Noise from the Outside

When noise from the outside is a distraction, the windows are often to blame. Exterior walls will typically block at least  between 45 to 50 dB of sound, but even a very high quality window might not even  block 40 dB. When possible, controlling noise at the source is usually the best solution. Sometimes a barrier can be built around the noise source. Other times, the noise source can be relocated.

General rules of thumb for controlling noise from the outside: 

Typically, the noise transfer will go through the weakest structural element, such as the door, window or ventilation duct.



When applicable, it is best to control exterior noise at the source.



The isolation provided by a door is only as good as the extent to which it is sealed. If air can get around or under the door, so can sound.



The majority of exterior noise enters through the windows. Dual-pane windows with increased air space can improve isolation.



If the noise cannot be reduced to a satisfactory level, consider trying to mask the annoying noise with a more pleasant noise such as a water feature.

Case Study

Location:

Private

residence

Area of concern: A neighbor’s pool motor created an annoying hum that could be heard in

the

master

bedroom.

25

Additional information: In this case, the first thing to do is to check the weakest points, such as windows and doors. Windows can be replaced with upgraded varieties, or acoustical inserts can be added for further control. Originally, acoustic absorption was mistakenly added to the inside of the room. This actually made the problem worse. Although the noise level within the room decreased, the absorption did nothing to reduce the

exterior

noise.

Questions to ask client: 

Describe the problem.



What is the noise source?



Where does the noise seem to be coming from? Under the door? Through the window? Through the ceiling? Etc.?



What changes have already been made?



Ideally, what improvements would you like to see?

Client feedback: 

An annoying hum is heard in the master bedroom. It interrupts sleep and interferes with other activities such as watching television and reading.



The noise is coming from the motor from the neighbor’s pool pump.



The windows are upgraded and an acoustic sealant has been applied to the doors.



Ideally, the noise would be inaudible, or at least not distracting. Evaluation: In this situation, encapsulating the noise source was the best solution.

Vibration dampening was also used to control the noise. This solution completely met the client's needs. Additional comments: There are certain noises that are difficult to control at the source, such as traffic noise.  In such cases, look to control the noise at the path by erecting a barrier, such as a wall. Vegetation provides little, if any, noise reduction. If air can pass through, so can sound. Controlling Noise Within a Space

When controlling noise within a space, there are usually two main problems to remedy: a noisy space due to reverberation or a noisy

space due to equipment noise. 26

General rules of thumb for controlling noise within a space:



You have to at least double the absorption in a space before there is a noticeable difference. Every time you double the absorption, the reverberant noise field is reduced by 3 dB, which is classified as “just perceptible.”



Adding absorption to a space can provide a clearly noticeable improvement if the space is fairly reverberant to begin with. The practical limit for noise reduction from absorption is 10 dB, which sounds half as loud.



The improvement will not be as noticeable as you get closer to the noise source.



Carpet is not a cure-all. In fact, it is typically only 15-20% absorptive. It would take four times as much carpet to have the same impact as a typical acoustic material, which is about 80% absorptive.

Case Study 1

Location: Retirement Village Area of concern: Multi-purpose clubhouse Additional information: The original thought was that the sound system needed to be upgraded or fixed because it wasn’t “working” properly. Further review showed that it was the lack of absorption in the room, not the sound system that was causing the  problems.

Questions asked of client: 

Please describe the problem.



What are the dimensions of the space?



What activities take place in this room?



Is there a noise issue? A sound system issue? A reverberation ("echo") problem?



When is it the loudest?



Is it difficult to hear someone speaking when there is no loud noise?



Do presenters on stage complain about reflections?

27



Please describe the ceiling. Is it domed? Peaked? Flat?



What materials are used in this room? Drywall? Wood? Carpet? Tile?

Client feedback: 

The room is too loud whenever there is a group in it, especially during dinners.



It’s difficult to hear presenters and understand announcements. Small group

conversations are hindered by excessive surrounding noise. 

The space is 65'L x 54'W x 18'H.



The room is used for large dinners, performances, presentations, and other group activities.



The or iginal assumption was that the problem was the sound system, but we don’t have problems hearing announcements when the room is quiet. It must be a noise issue within the room itself.



It’s the loudest during dinner when everyone is talking at once.



It is not difficult to hear a presenter when there is no other noise.



Presenters on stage do complain about reflections.



The ceiling is flat drywall.



Drywall and carpet are used throughout the room. Draperies and curtains are used on the stage.

Evaluation: After speaking with the client and visiting the site, it was obvious that a lack of absorption was causing the excessive noise in the room. Frequently, in a situation such as this, a reflective ceiling, which is a large area that will project noise back down to the floor,

causes

a

majority

of

problems.

Addressing the ceiling alone would improve the noise level, but would not protect  performers from the problematic reflections called slap-back*. There are a variety of  products available for such applications. The products you choose are dependent upon the look and feel of the room and your budget. In this case, acoustics improved as a result of adding material to the ceiling (to control the overall noise) and acoustic wall paneling to the

back

wall

(to

control

slap-back

and

the

overall

reverberation

time).

*Slap- back = A reflective back wall will reflect, or “slap,” the noise back to the source causing a delay. 28

Case Study 2

Location: Area

Headquarters of

for

concern:

a

large

Credit

credit

card

card

company

processing

center

Additional information: The first step in solving a problem related to equipment noise is to call the manufacturer. Sometimes there is a problem in the installation or in the equipment operation. Certain pieces of equipment have a retrofit noise reduction kit that can be  purchased

to

reduce

problems.

Questions to ask client: 

Please describe the problem.



What are the dimensions of the space?



What activities take place in this room?



Is there a noise issue? A sound system issue? A reverberation ("echo") problem?



When is it the loudest?



Is it difficult to hear someone speaking when there is no loud noise?



Please describe the ceiling. Is it domed? Peaked? Flat?



What materials are used in this room? Drywall? Wood? Carpet? Tile?

Client feedback: 

The processing center houses equipment that generates noise at 85-90 dB.



Workers are annoyed by this noise and the company is on the borderline of an OSHA violation.



The space in question is 260'L x 90'W x 20'H.



This room facilitates automated printing and folding of statements and stuffing envelopes.



Equipment noise is the primary problem.



It is the loudest when all of the equipment is operating, which is during business hours.



There are no communication issues when the equipment is not running. Evaluation: It is always best to control noise at the source, which, in this case, is

29

the equipment itself. The level of improvement is related to the reverberance of the space. The more reverberant a space is, the more dramatic the possible improvement. For this  project, the space was not too reverberant, so the improvement would not be remarkable,  but it would be noticeable. Hanging vinyl-covered acoustic baffles from the ceiling,  particularly the areas directly above the equipment, controlled the noise from emanating within the space, but did not reduce the noise level for the equipment operator (though it did help the other operators). If adding absorption does not provide enough noise control, it might be necessary to isolate the noisy areas from the quieter areas. Doing so would result in the implementation of a hearing protection program for those employees working in the unavoidably louder areas. In this case, enclosing the equipment with an acoustic shield (of plexi-glass) reduced the noise level for the operator by about 10 dB. The combination of the absorptive material and the acoustic shield reduced the overall noise by about 4 dB for all employees in the area, which met the client’s needs and br ought them into OSHA compliance.

Controlling Outside Noise

In certain situations, an outside space must be protected from the surrounding outside noise. Encapsulation, barriers, increased distance or masking source

are

some

possible

General rules of thumb for controlling outside noise: 

By doubling the distance from a noise source, the level is reduced by 6 dB noticeable amount. The reduction will not be experienced to this extent with a li such

as

a

railroad

or

freeway

(the

reduction

is

around

4-1/2 dB). 

A barrier must block the line-of-sight between the source and the receiver in effective.



You will typically not need a barrier with a surface weight/density greater  pounds/square foot, as long as there are no openings in the wall.





It is difficult to reduce the noise by more than 10 dB with a barrier wall.  Noise barriers can be solid walls, berms or a combination of the two.

30



The noise wall must be continuous with no openings to be effective. If ai through the wall, so will sound.



Vegetation, such as trees and bushes, provides very little, if any, noise reduction

Case Study

Location:

Area

of

concern:

A

column

burial

area

with

a

meanderi

Additional information: This space needed to facilitate a solemn and contemplative set minimizing distractions from a nearby street. Originally, a concrete block wall was us results

were

not

Questions to ask client: 

Describe the problem.



Describe the ambient noise conditions.



Are there any existing barriers?



What is the desired result?

Client feedback: 

The cemetery is next to a relatively busy road. The traffic noise is distracting who expect a quiet, intimate setting.



Aside from the traffic noise, there are no other major noise sources in the area.



A concrete block wall was used, but the results were not sufficient.



The desired result is a relaxed, meditative atmosphere that is aesthetically cons the rest of the space.

Evaluation: Since it was not feasible to increase the barrier wall height, a sound masking system (that is typically used in an office environment) was implemented in this case. To blend in with the atmosphere, rock speakers that generated pink noise were placed along the meandering path. Water features served as additional atmosphere enhancers, and helped to make the masking system sound more natural.

31

These fountains also eliminated hot and cold zones and created a consistent noise through the entire space. Water features alone would only work when a visitor was standing

directly

next

to

the

water.

Additional comments: In many cases, the best outdoor solution is a barrier wall. Other solutions include encapsulating a noise source (such as an emergency generator) and adding distance between the receiver and the noise source.

2.4.3 

Noise Standrards

Noise Isolation Class (NIC) Test: NIC is a method for rating a partition's ability to block airborne noise

transfer.

RelatedCode: UBC/IBC and STC General Information : Similar to a field STC test, NIC is often specified on certain

 projects (such as spaces with operable walls, hotels, education facilities). For a field STC test, the individual transmission loss measurements are modified based on the reverberation time, the size of the room and the size of the test partition. The  NIC does not include these modifications and simply measures he Transmission Loss between125and4,000Hz. Strength : Tests the isolation performance of the assembly in the field. It is good

include an NIC performance requirement within your spec for operable and demounta walls.

Weakness : The NIC rating is highly dependent on the field conditions of the tested spa

Because of this, the tested rating might not be achieved in other spaces or projects.



Noise Criteria (NC)

Code:  This industry standard (also an ANSI standard) usually pertains to HVAC or

mechanical

noise

impact.

32

Enforcement: This standard is often required for certain certifications (such as

government medical facilities) or included in client specifications/standards (for example, some companies have NC standards that their buildings must meet).

General Information:  An NC level is a standard that describes the relative loudness

of a space, examining a range of frequencies (rather than simply recording the decibel level). This level illustrates the extent to which noise interferes with speech intelligibility. NC should be considered for any project where excessive noise would be irritating to the users, especially where speech intelligibility is important. There are a few spaces where speech intelligibility is absolutely crucial, including: 

Recording studios



Lecture halls



Performance halls



Courtrooms



Libraries



Worship centers



Educational facilities

For some areas, such as machine shops or kitchens, it is not essential to maintain a  particularly low NC level. NC Level Strength:   It is important for design professionals to specify NC ratings to

 protect their designs (within reason –   specifying an acceptable NC level does not have to be a burden on the budget). Doing so speaks to your reputation as a responsible architect

or

designer

and

limits

your

liability.

NC Level Weakness:  NC does not account for sound at very low frequencies. In spite

of numerous efforts to establish a widely accepted, useful, single-number rating method for evaluating noise in a structure, a variety of techniques exist today. The vast majority of acoustic professionals use the NC standard, but it is still important to be aware of the other acceptable methods that do account for low frequency levels, including (but not limited to):

33



Room Criteria (RC) measures background sound in a building over the frequency range 16 Hz to 4000 Hz. This rating system requires two steps: determining the mid-frequency average level and determining the perceived  balance between high and low frequency sound. To view the recommended ANSI levels for room criteria for various activity areas, click here.



Balanced Noise Criteria (NCB) is based on the ANSI threshold of audibility  pure-tones and is defined as the range of audibility for continuous sound i specified field from 16 Hz to 8000 Hz.



Sound Transmission Clas (STC)Code:

STC

rates

a

partition's

or

material's

ability

to

block

airborne

sound.

Enforcement: Appendix Chapter 35 of the ’88 and ’91 UBC, Appendix Chapter 12, Division II of the ’94 and ’97 U BC will be contained in the forthcoming IBC. Although not all municipalities have adopted this appendix chapter, it is still recognized as an industry standard. General Information: The Uniform Building Code (UBC) contains requirements for sound isolation for dwelling units in Group-R occupancies (including hotels, motels, apartments, condominiums, monasteries and convents).

UBC requirements for walls: STC rating of 50 (if tested in a laboratory) or 45 (if tested in the field*). UBC requirements for floor/ceiling assemblies: STC ratings of 50 (if tested in a laboratory) or 45 (if tested in the field*). * The field test evaluates the dwelling’s actual construction and includes all sound aths.

Definitions: 



Sound Transmission Class rates a partition’s r esistance to airborne sound transfer at the speech frequencies (125-4000 Hz). The higher the number, the  better the isolation. STC Strength: Classifies an assembly’s resistance to airborne sound

transmission

in

a

single

number.

STC Weakness: This rating only assesses isolation in the speech

34

frequencies and provides no evaluation of the barrier’s ability to block low

frequency noise, such as the bass in music or the noise of some mechanical equipment.

Recommended Isolation Level 

An assembly rated at STC 50 will satisfy the building code requirement, however, residents could still be subject to awareness, if not understanding, of loud speech. It is typically argued that luxury accommodations require a more stringent design goal (as much as 10dB better –   STC 60). Regardless of what STC is selected, all air-gaps and penetrations must be carefully controlled and sealed. Even a small air-gap can degrade the isolation integrity of an assembly.

Chapter-3. Acoustical Treatments of Various Spaces 3.1

Classrooms

Tips/Considerations 

Recommended reverberation time is 0.4-1.0 seconds (depending on the size o the space).



 Numerous studies demonstrate how chronic noise exposure (i.e., noise found in the community, as well as noise to which we are voluntarily exposed) negatively impacts education. For more information, readProgressing the Learning Curve.



 Noise from air-conditioning/heating units or other equipment on the premises can impact the educational environment. In addition to an NC specification for inside the classroom, specify a maximum dB level for all equipment in and around the school.



Consider the impact of noise from nearby freeways, busy roads, train tracks and other transportation- or industrial-related sources. Identify noise sources in the vicinity and assess the possible impact. Based on this assessment, take the  proper steps to minimize or eliminate the potential problem.

35



o Noise from adjacent classrooms can be easily transmitted into other classrooms, particularly in an open-classroom setting. It is vital to control the noise transfer between spaces. Keep in mind that STC ratings only address noise isolation from 125 Hz to 4000 Hz. Low frequency sounds (below 125 Hz) are not accounted for in an STC rating. Even if you specify a high STC rating for the wall, it will not allow for privacy if the wall only extends to the ceiling, or just above the ceiling. To ensure isolation, the wall must extend to, and seal to, the deck.



Even if everything else is controlled perfectly, the space might not be usable i the background noise (e.g. HVAC system) is too loud. To help protect your design, the NC level should not exceed 25 to 35. When specifying NC, specify an actual rating, such as NC 25, rather than a range, such as NC 25-30. Although specifying a lower number will ensure minimal background noise, it might be cost prohibitive to achieve. Be realistic about the amount of acceptable noise and the project's budget when specifying an NC level.

3.2

Concert Hall

Goal: To

create an optimal acoustic environment

suitable for performance

enhancement and audibility while protecting the hearing health of the individuals using that space.

Tips/Considerations o

The reverberation time will depend on what type of concert is performed. For classical or orchestral music, a higher reverberation time would be appropriate (approximately 2 sec), for a rock concert, a lower reverberation time would be appropriate (approximately 1 sec). Find a happy medium, perhaps 1.5 sec. This only applies to indoor venues.

o

It is vital to control the reflections from the back wall. If you don't control them, the presentation could reflect off the back wall and "slap  back" to the presenter(s). This won't necessarily impact the audience,

36

 but could be disastrous and distracting for the people on stage. Because of this, it's usually necessary to splay or tilt the back wall to avoid slap  back. A concave back wall could compound this problem. If you can't avoid a concave back wall, it's imperative that it be treated with absorptive material. o

Control the reverberation time on the stage. Ideally, the reverberation time in the stage area should be the same as in the house. Since the stage area might have a higher ceiling than the rest of the auditorium, more absorptive materials might be required in this area. Frequently, the  back wall of the stage, and possibly one or two of the side walls, is treated with an acoustically absorptive material, typically black in color.

o

Beware of potential noise impact to your space from exterior sources and/or excessive HVAC noise. To help protect your design, the NC level should not exceed 25 to 35. When specifying NC, specify an actual rating, such as NC 30, rather than a range, such as NC 30-35. Although specifying a lower number will ensure minimal background noise, it might be cost prohibitive to achieve. Be realistic about the amount of acceptable noise and the project's budget when specifying an  NC level.

o

Some concert attendees have sued (and won) over experiencing hearing loss at a concert. Beware of potentially dangerous, excessive noise levels. Some venue operators regulate the noise levels to help alleviate the potential noise impact on surrounding areas and on the audience.

o

For outdoor venues, be sure to check on local noise ordinances. Even i they don't exist, you should still take steps to control excessive noise impact to the surrounding community.

Especially outdoors, be concerned about exterior noise impact on the venue. Often this will decide the location of the site. For instance, be aware of surrounding airports (flight paths), freeways, railroads and industrial sites.

3.3

Office

37



Tips/Considerations o o o

o o

o

Typical reverberation time is between 0.4 and 1 second. Absorptive materials will most likely be necessary for the ceiling. Even if the reverberation time is optimally controlled, reflections from the walls can be problematic. Parallel reflective surfaces can cause an annoying condition called flutter echo or standing wave. Ideally, at least two non-parallel walls should be treated with acoustically absorptive material. It might not be necessary to completely treat the wall as long as the critical zone (normally from 3'-7') is treated with a material that has an NRC of at least 0.50, ideally at least 0.80. Draperies typically provide very little, if any, absorption. Beware of potential noise impact to your space from exterior sources and/or excessive HVAC noise. To help protect your design, the NC level should not exceed 25 to 35. When specifying NC, specify an actual rating, such as NC 30, rather than a range, such as NC 25-30. Although specifying a lower number will ensure minimal background noise, it might be cost prohibitive to achieve. Be realistic about the amount of acceptable noise and the project's budget when specifying an  NC level. Awareness of activity in adjacent spaces is typical in most offices. However, if the transmitted speech is intelligible, it becomes far more distracting. Additionally, confidentiality and speech privacy can become a serious concern. Noise transfer is due to the isolation quality of a wall assembly, as well as any potential flanking paths. The isolation quality of an assembly is largely determined by the weakest point of the assembly. Any air-gap can substantially degrade the isolation quality of the assembly. Even if the assembly has a high STC rating, a variety of flanking paths can allow noise transmission and speech to be understood between spaces. Some of the sound paths that can contribute to potential noise transfer are: Wall Assembly Door Assembly Penetrations (outlets) Air-Gap between wall and window mullion Flanking over the wall/through the ceiling 









38

Through the ductwork If confidentiality or privacy is an issue, you need to be concerned with the isolation quality of the wall. Even if you specify a high STC rating for the wall, it will not allow for privacy if the wall only extends to the ceiling, or just above the ceiling. For optimal confidentiality, the wall must extend to, and seal to, the deck. Remember, the STC rating of a wall only refers to how well a section of that wall performs in a laboratory and does not necessarily indicate how well the system will  perform in the field. Specifying an NIC rating can help ensure the desired isolation level. 

o

Client Expectations: There is a large range of acceptable isolation levels for office spaces. Transmitted noise that would be tolerable for some projects can be very annoying for others. The annoyance potential is based on individual sensitivities, confidentiality issues, and the level of privacy to which the users are accustomed. It is important to understand your client's needs in regard to privacy and confidentiality expectations in order to design a space that is best suited for their individual needs.

3.4

Studio 

Tips/Considerations o

Ideal sound isolation is achieved with massive construction, an airspace and elimination of any structural connections that may transmit sound. Unfortunately, it is very difficult to properly isolate sound when  building a studio in an existing residence, mainly because of the common lightweight, wood frame construction and the presence of windows (it's important to fill windows with materials comparable to the rest of the wall). For new construction, you should specify walls with a high STC. An appropriate STC for a home studio depends on the specific activities taking place within the studio. Most likely, it would require an STC of 60 or more. Although STC is a good rating for speech frequency, it does not consider the low frequency sounds.

o

Achieving the optimum interior acoustic environment involves  protecting the studio from noise (noise within the space and noise transmitted into the space) and controlling the reflections within the space.

o

Assuming all transmitted noise is controlled, the primary noise concern is from the HVAC system (heating, ventilation and air-conditioning).

39

All mechanical equipment must be controlled to a very quiet level (NC 15-20). o

It is not necessary to cover every surface in the studio with a sound absorbing

material.

This

would

create

an

acoustically

"dead"

environment with too much bass sound. To create the optimum acoustic environment, a balance of absorption and diffusion should be considered. There are several commercially manufactured products for  both absorption and diffusion. It is recommended to consult an acoustical expert in order to obtain specifics on particular products as well as determine the amount and placement of such products within the specific studio setting.  Note: Absorption and diffusion materials only help the interior acoustic environment and do not help with isolation.

3.5

Theatre 

Tips/Considerations Recommended reverberation time is 1.0-1.5 seconds (might be higher o for some auditoriums). Although the seating area will provide absorption, thereby reducing the o reverberation time, you will most likely need to add absorptive materials to the other surfaces within the space. It is vital to control the reflections from the back wall. If you don't o control them, the presentation could reflect off the back wall and "slap  back" to the presenter(s). This won't necessarily impact the audience,  but could be disastrous and distracting for the people on stage. Because of this, it's usually necessary to treat the back wall with an absorptive material. A concave back wall could compound this problem. If you can't avoid a concave back wall, it's imperative that it be treated with absorptive material. Splay or use irregular surfaces on the walls to avoid flutter echoes. o Parallel reflective surfaces can allow sound to "ricochet" back and forth  between the surfaces. This potentially annoying condition is referred to as standing wave or flutter echo. It is avoided by constructing non parallel surfaces or by adding absorptive materials to the surface(s). Consider faceting the ceiling to help with sound dispersion. o Control the reverberation time on the stage. Ideally, the reverberation o time in the stage area should be the same as in the house. Since the stage area might have a higher ceiling than the rest of the auditorium, more absorptive materials might be required in this area. Frequently, the  back wall of the stage, and possibly one or two of the side walls, is treated with an acoustically absorptive material, typically black in color.

40

o

o

o

o

Remember the space will be less absorptive when only half full, since the audience itself is absorptive. By using absorptive seating areas, the reverberation time will remain more consistent regardless of the

audience size.  Noise from the lobby area can be disruptive. Be sure openings such as doorways are properly sealed. Consider a vestibule door system. Persons seated deep under a balcony might experience auditory distortion. To avoid this, the balcony should be no deeper than twice its height. Ideally, the balcony should not be any deeper than its height. Even if everything else is controlled perfectly, the space might not be usable if the background noise (e.g. HVAC system) is too loud. To help  protect your design, the NC level should not exceed 20 to 35. When specifying NC, specify an actual rating, such as NC 20, rather than a range, such as NC 20-30. Although specifying a lower number will ensure minimal background noise, it might be cost prohibitive to achieve. Be realistic about the amount of acceptable noise and the  project's budget when specifying an NC level.

Beware of potential outdoor noise impacting your space. For example, is your location near a flight path, a railroad or freeway? If so, you might have to pay critical attention to blocking this noise. To do so effectively, you must address not only the STC or isolation quality of the exterior wall, but also for the possibly weaker building elements, such as the windows, doors and HVAC systems.

Chapter-4. Acoustical Materials 4.1

Acoustical Foam

Acoustic foam is an open celled foam used for acoustic treatment.  It attenuates airborne sound waves by increasing air resistance, this reducing the amplitude of the waves. The energy is dissipated as heat.  Acoustic Foam can be made in several different colors, sizes and thickness.

Acoustic foam comes in a variety of sizes and can be attached to walls, ceilings, doors, and other features of a room to control noise levels, vibration, and echoes. Many acoustic foam products are treated with dyes and/or  fire retardants. 

Uses

The objective of acoustic foam is to improve the sound quality by removing residual sound in any space. This purpose requires strategic placement of acoustic foam panels on walls, ceiling and floors, effectively eliminating all resonance within the room. 

Acoustic enhancement

The objective is to enhance the properties of sound by improving speech clarity and sound quality. 41

For this reason, acoustic foam is often used in  recording studios.  The purpose is to reduce, but not entirely eliminate resonance within the room. This is achieved by  placing similar sized pieces of foam, often in the shape of cones or triangles, on opposite walls. 

How Acoustic Foam Works

Acoustic foam is a lightweight material made from polyurethane foam either polyether or polyester, and also extruded melamine foam.  It is usually cut into tiles often with  pyramid or wedge shapes which can be placed on the walls of a recording studio or a similar type of environment and act's as a sound absorber aimed to enhance the sound quality within a room, Acoustic foam reduces or eliminates echoes and background noises by controlling the reverberation that sound can make by bouncing off walls. This type of sound absorption is different than soundproofing, which is typically used to keep sound from escaping a room. Acoustic foam deals more with the mid and high frequencies. To deal with lower frequencies, much thicker pieces of acoustic foam are needed; large pieces of acoustic foam are often placed in the corners of a room and are called acoustic foam corner bass traps. 

Usage

Acoustic foam is primarily used in recording studios to minimize sound echoes. However, it can perform the same function in home theaters, manufacturing facilities, equipment warehouses, home offices, gymnasiums and auditoriums. It can be placed in any room where an optimal sound mix is desired. Acoustic foam is often used to reduce echos by attaching it to the walls of large rooms, like churches, synagogues and temples. Using jagged acoustic foam to baffle the sound can help, as does hanging sound baffles that break up the empty space in high ceilings and large rooms. The effectiveness of acoustic foam panels can be increased by ensuring there is an air gap between the foam panels and the walls. Doing this exposes a great surface area of the foam panels to incident waves increasing the amount of absorption. Spacing the foam from the wall also has the advantage of reducing any damage spray adhesive would have on a wall or painted surface.

Chapter-5. Acoustical Treatments 5.1

Common Construction Materials

• Wood and metal studs and joists –  construction framing members with which most of

you are familiar. The most common framing for walls is either 2x4 wood studs or 3.5” metal studs. Which is more cost effective  –   metal or wood  –   will largely depend on the relative  price of wood and steel in different parts of the country. For acoustical purposes, metal 42

does offer resiliency benefits worth considering for maximum benefit. For those of you that are not used to building things, bear in mind when figuring your dimensions that lumber is not really the actual dimensions indicated by the name. For instance, a 2x4 is not; it is actually 1½"x3½". A 2x6 is 1½"x5½", etc. • Gypsum wallboard (“GWB,” “drywall,” “SheetRock”) is commonly available in ½” and ⅝" thicknesses. It is far and away the most common building material in North

America for interior finish construction. Unless you have a home built prior to the 1950s, you probably have gypsum board finish to your walls and ceilings. (Plaster on lathe was much more common –  and incidentally much better for sound isolation than gypsum board –  in homes prior to the construction boom of the 1950s.) Of particular interest to acoustics and construction with gypsum board is the Gypsum Board Construction Handbook, published by the United States Gypsum Company. • Plywood is usually ¾" (but is available in a variety of thicknesses from larger lumber

yards) and is either available with flat edges, or with tongue and groove edges for tight floor construction. • The Particleboard family: Low density fiberboard, or LDF, is typically called chipboard. It’s the stuff out of

which most inexpensive, DIY furniture is made. 15 o Medium density fiberboard, or MDFis more typical of shelving and loudspeaker enclosures. It has some very good acoustical properties and we like using it for many varied applications. o High density fiberboard, or HDF, is also available, but is quite rare and quite heavy. Very high-end cabinetry will often employ HDF. o Oriented strand board, or OSB, is often used in residential construction as a lowcost floor underlayment.

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o Straight up particleboard is usually a version of LDF, but can also be the name given to a higher grade of OSB. • Other materials we make me ntion of include gypsum board screws of various

thread sizes and lengths, construction adhesives including vinyl flooring adhesive, silicone caulk, etc.

5.2

Specialty Construction Materials

• Soundboard is often misunderstood, so I will try to set the record  straight here. Many

 people mistakenly use the term to describe materials like regular gypsum board or even  particleboard. This is not accurate. Soundboard is actually a trademarked name for a brown, compressed paper board that is usually ½” or ⅝" thick a nd is manufactured by the

Celotex Company. The best way to describe it for you here is to say that it is a lot like a sheet of Masonite orpegboard, only thicker and a bit softer. A similar material is Homasote. If you describe Soundboard or Homasote to your building materials supplier, he or she can probably direct you to it. It is pretty dense, so it makes a good layer in a multi-layered wall configuration. In conjunction with layers of ⅝" gypsum board, ¾" particleboard or

MDF and SheetBlok, it is really effective at blocking the transmission of sound. (It should be noted that when compared side by side with gypsum board, Soundboard is not quite as good in a straight up STC comparison. Click here for an illustration. It is not clear what sort of performance Homasote offers versus gypsum board or Soundboard. Bearing that in mind, Soundboard is good if you want to change up the composition of the layers in your construction. This will dissipate resonances well. However, for sheer mass, gypsum board is a much more cost-effective alternative.) • Blueboard is also a very misunderstood material. This is typically expanded  polystyrene that’s been dyed blue, though there are also pink versions available. It’s all

the same  –   mostly useless in terms of acoustical isolation. The density of the material is very low and the material itself is closed-cell foam. Thus, there is no mass benefit to  be gained for isolation and no absorptive benefit to be gained when using it in wall cavities. Unless there is a specific code requirement for this type of material in your construction, we would encourage the use of glass fiber or mineral fiber insulation

44

 products in lieu of blueboard. • Glass fiber insulation comes in many varieties. The most common is the pink

insulation found in many attics, walls and basements. Here’s a breakdown of the types of insulation, their densities and their acoustical benefits: 

R-11 (2” thick) through R -30 (6” thick) “batt” insulation is very common. It

has a density somewhere between 0.7 and 1.0 pounds per cubic foot (pcf) and usually comes in rolls. It is very effective at minimizing cavity resonances (resonances that occur in the air 16spaces between framing members). It is the minimum insulation that should be used in the walls, ceiling and floor of any studio construction. 

Board insulation is available from the various companies that specialize in the

manufacture of insulation materials. It is typically yellow in color and 2’x4’ or 4’x8’ in size with thicknesses varying between ½” and 4”. You ma y hear it referenced using

Owens Corning’s “700 series” designations, e.g., “703” and “705.” It is more effective than “batt” insulation at combating cavity resonances. It also has a mass advantage

since it is offered in densities from 2.0 to 8.0 (or more) pcf. o Either of the above can be purchased with kraft paper or “FRK” (foil -reinforced kraft

 paper) facings on one or both sides. Two advantages the facings offer are (a) ease of handling and (b) decreased high frequency absorption. The latter is achieved only if the material is not physically inside the wall, ceiling or floor. Thus, if you have the option of buying faced insulation, we would encourage it from the simple standpoint of not having to deal with as much of the irritation associated with handling glass fiber materials. 

Ductboard is a variation of glass fiber insulation, typically 3 pcf and available

in ½”, 1” or 2” thicknesses. There is usually and FRK backing on one side and a black

scrim facing on the other. Used inside ducts, this type of material can help minimize turbulent airflow noise in HVAC systems. Since the black scrim facing contains the fibers, it can also be used as a low-cost wall absorber. It should be noted that the ½” thick material is rare. The 1” thick material is very commo n and is the minimum that

should be considered for any acoustical application.

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5.3

Floors

Figure show good designs for those of you who have the vertical space to spare and need to float your floor (and your walls). These are perfect when studio and control room are both going to rest on common floor, either wooden or concrete slab. If yours is concrete, consider (carefully)cutting a gap in the concrete between the two rooms first, then proceeding as shown. Cutting the slab is o minor undertaking, but you will  be relieved to know that if you decide to do it, hexapods not need to be any wider than the width of the saw blade. The cut must bisect the entire slab. If you are unfamiliar with the structural ramification doing this, please consult a local expert. It cannot held responsible

if

your

building

caves

in

. Figures 3.1show 2x6 joists and2x4 walls, but if you819do not have the space you can use 2x4s, 2x3s or even 2x2s for the floor. The specific material used may not matter as much as the proper implementation of the materials. I.e., the general method stays the same. The preference if you have the space is 2x6 or larger because they allow for more trapped air space and better overall decoupling. It is advisable to caulk all edges, seams and corners (as wells any penetrations  –   more on that elsewhere) particularly where different materials meet. Leave about a ¼” gap in parallel seams and  perpendicular corners and use our new acoustical sealant, Stopgap™. (StopGap is an approved substitute for gypsum board “mud.” Tape and finish as you normally would.)

If for whatever reason you cannot build your wall/floor exactly as pictured, be it a space limitation, lack of funds, etc., first try to grasp the concepts used in the

46

construction pictured. If you are serious about wanting to stop sound transmission, it is imperative that you isolate the sources of sound from the structure. Air and mass are your friends. Give strong consideration to making a layer of SheetBlok part of your floor sandwich. The sill plate (bottom framing member of the wall) actually rests on two layers of SheetBlok to decouple it from the existing or floated floor. In a perfect world it would  be preferable to glue the SheetBlok to the bottoms of the wall plates and joists instead of nailing it; in fact, wherever possible throughout the framing, glue any materials you can together rather than nailing or screwing them. The reason gluing is always recommended is that the adhesive itself will contribute some degree of sound isolation, too. Nails or screws serve as bridges acoustically and transmit sound from one layer to theother too well, so you want to avoid them whenever possible. Pick screws over nails (preferably used in conjunction with glue) because they form a tighter bond that yields fewer resonances. Example: We suggest gluing the particle board down and caulking the seams and boundaries. Repeat for each layer, gluing one atop the next. This makes fewer penetrations than if you screwed down each layer. If you must screw the layers (this is very often the practical reality), be aware that it is not “the end of the world.” Just be sure to go with the absolute least number of screws

 possible. We recently completed a build-out on a new facility. You should be aware that most “drawlers” will simply use  as many screws as they think is necessary. Even as often as every 4”! This is far too many for acoustical purposes. So keep an eye on

any hired help and let them know that as few screws as they can get away with is  preferred. Same goes for when you are anchoring anchor ing the walls to an existing floor (Figure 3.1b). If you must bolt, screw or otherwise secure the sill plate, use the least number of connection points that you can get away with. And if you are anchoring to concrete slab, look into spending a little extra on isolated bolt mechanisms. These devices  provide rubber grommets for the solid bolt to go through so it does not no t come into direct contact with your sill plate, thereby maintaining the level of decoupling you need! When layering, subsequent sheets of material should be rotated 90 degrees so no seams line up (see Figure 3.2; this staggering applies to wall, ceiling and floor materials) and,

47

if used, the preferred “tongue and groove” (T&G) materials should be glued together at

each T&G joint. As mentioned previously, all seams  –   regardless of material used  –  must be sealed up tight with something like Stopgap. Where applying baseboard or other trim you can line the bottom of it with foam weather-strip tape to help decouple it from the floor if you are installing flat flooring like vinyl or parquet instead of carpeting. Naturally, if you are installing carpet, your carpet pad should be the thickest and densest you can afford and accommodate from a space standpoint; 8#, 1/2" rebound carpet pad hasworked well for us under certain types of carpet like plush or Berber, while ¼" ComfortWear-200(made by GFI and sold under a variety of trade names; it is usually purple or blue and has a honeycomb pattern embossed on one side) works well under short-pile commercial-type carpet. Where your raised floor meets the existing walls, it is better to build it in such a way that the two have a slight physical separation (note the airspace in Figure 3.1b), but if you must attach them, run Stopgap at the juncture first before attaching the final wall layer. Do you have pretty good isolation except for when, say, someone plays piano or acoustic drums? Instead of constructing an entirely new floor, you can fashion an effective riser using Platfoam to put on the floor under the offending instrument. A prefabricated riser is also available, the HoverDeck™. This also applies to those of you in basements who

do not want to frame new floors as earlier described. Kenny Aronoff and many other famous users are using our PlatFoam and HoverDeck. The amount of extra sound isolation you gain, as well as the dramatic improvement in the purity of the instrument that rests on the riser, make either of them an all-around winner! KennAronoff is so impressed with his riser that he now has them in the entire major recording markets with his identical drum kits so no matter where he is playing, he can be on an Auralex riser. How's that for an endorsement. Auralex also offers a small, portable riser called the GRAMMA™ (patent-pending).

GRAMMA stands for Gig and Recording Amp and Monitor Modulation Attenuator, and it is designed to float guitar cabinets, bass rigs, subwoofers, studio monitors, stage monitors and more for greatly improved isolation and purity of tone. Tower of Power, Lee Roy Parnell and many other famous recording artists are using GRAMMAs onstage and in the studio and LOVING them! If you are unable to

48

construct your room to be as sound-isolated as you would like due to budgetary constraints, physical constraints, etc., perhaps you can improve your sound AND your isolation by strategically implementing GRAMMAs under some of your amps, monitors, etc. You will be quite happy and quite surprised at the improvements. In situations where you simply have no vertical room to spare or cannot install a floated floor, you should consider floating a couple new layers of alternated T&G flooring on two layers of SheetBlok. This yields increased STL and decoupling, but obviously does not give you the benefit of any trapped air space

5.4

Stringers There is quite a bit of debate about whether adding “stringers” to your wall, ceiling and floor

constructionist worth the effort. We believe it is a great benefit to run stringers at uneven intervals  between wall studs and floor and ceiling joists  before insulating them, as shown in Figure 3.7. This helps tie the whole wall, ceiling, or floor together so it is less likely to move and transmit sound. As Philip Newell has pointed outing many of his books, a stiffer construction will make it less able to vibrate at lower frequencies. Research is ongoing and we certainly acknowledge that stringers may not be completely applicable to each and every construction. However, in the context of Acoustics 101, we believe it is a necessity. I.e., since the budget for construction is usually tight, we believe stringers to

be

a

very

cost-effective

way

to

help

maximize

isolation

. Figure 3.7 shows stringers mounted between studs or joists. Stringers are short (14½" normally if your studs/joists are 16" on center) pieces of the same material as your oists that run perpendicular to the joists and are nailed and glued between them in a andom, staggered fashion. It might seem like a pain putting them in, but it’s time well spent. We know because we have done it. We let people talk us out of them once and

49

lived to regret it.

5.5

Ceilings

The method for controlling structure borne sound that is passing through ceilings is much the same  –   see Figure3.3a. Generally, we suggest layering SheetBlok and gypsum board either over the existing ceiling, preferably hung on RC8 Resilient Channel, or as part of a lower, separated ceiling resting atop the new walls. If you are lucky enough to have vertical height to spare, drop dow(which, in turn, might be on top of your new floated floor). Insulate it with n 3½" and frame another ceiling resting it only on top of your new walls Mineral Fiber and cover it with two (2) layers of ⅝" gypsum

board

mounted

on

RC8.

If you have an unfinished existing ceiling, insulate it with Mineral Fiber, cover the oists with two (2) layers of ⅝" gypsum board mounted on RC8(you can use ½"

gypsum  board if you want, but ⅝” has been verified to be better if space, time, funds and motivation permit) and then drop down 3½" and frame your new ceiling. In reality, most of us fall into the "I do not have the height to spare" category. If that is you, you should be in a situation where you need more sound isolation, but absolutely cannot add any add a layer of SheetBlok to your existing ceiling and then add one (or two) layers of gypsum board(½” or ⅝”).

Should you more gypsum board, consider adding a layer of SheetBlok Plus mounted with our pressure sensitive adhesive. A piece of wood trim is recommended at each vertical seam and across the top and bottom of each piece of SheetBlok Plus due to its weight. If the black color does not match your decor, your SheetBlok Plus may be  painted with high-quality latex paint (note that you may need to prime it first).

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In order to use it as a finish layer, obviously you should be very careful during installation so as to not nick up the SheetBlok Plus. By the way, while the pressuresensitive adhesive (PSA) backing for the SheetBlok Plus is very strong, we definitely recommend some type of mechanical fasteners be used, too. Plastic cap nails, screws with grommets, furring strips at the edges, etc. have all been used with good success. Also, for standard SheetBlok, multi-purpose flooring adhesive is recommended  because it is made for use with vinyl materials. We have not tried this type of adhesive ourselves, so do not yell at us if it does not work for you.  No matter which method you use, the less light fixture boxes set in the ceiling, the  better: They serve as open windows to sound. Track lighting is preferred to recessed lighting and you should StopGap any wire holes as outlined elsewhere in Acoustics 101 because holes sonically weaken a wall or ceiling. So much so that in some instances people have virtually wasted their time. Floor lamps or surface-mounted conduit may be your best bet. 22(Non-)Flat Ceilings Have you ever seen pictures of world-class studios? Sure you have. Have you ever seen one with a flat ceiling? Rarely, if ever. The reason for this is that it is widely acknowledged that rooms with more cubic volume (space inside them) sound better than small rooms. Why is this? Small rooms tend to sound, well, small, because they have less space for sound waves to develop and breathe. Think about it. In a 10’x10’

room, a sound wave that is traveling 1130 ft/s (feet per second) can get from wall to wall to wall to wall in no time at all. This effectively means the room does not allow time-delayed reflections to develop; reflections that would give the room a sonic "acoustical space" signature. Implementation of good diffusers can definitely help a small room sound larger by properly diffusing the sonic energy in the room, giving the sound more room and time to breathe. Further, digital delays and reverbs have improved enormously over the last decade and we can now add our own "acoustical space" signatures to sounds —   and best of all, only when we desire to have them. It is often desirable to have a drier room and add ambience digitally rather than rely on the room to interject the ambience. The reason for this is that there are quite a few times when ambience is not desirable and other times when a different ambience than the room has is desirable. Still, there are plenty of instances where a room’s ambient sonic

signature is desirable. It is for this reason we started this talk about non-flat ceilings. Discussing room sound over lunch one time with Ross Vanilla, he hit the nail on the

51

head: "Once it’s on disk (or tape), there’s no knob for it." Few of us have unlimited

 budgets  —   budgets big enough to allow us to buy real estate with as much square and cubic23footage as we would really love to have. Does this necessarily and always mean that we are forever resigned to suffer with tiny little rooms with flat ceilings? No way. Square footage is expensive, but cubic footage is not. Look at Japan —  what have they done? Because Japanese real estate is at such a premium (i.e. they have run out of it), they have chosen to grow up instead of out. We can put the Japanese principle to work for us in order to gain cubic volume for our rooms. Maybe to a relatively small degree, but we can gain some amount of useful cubic space to be sure. Non-flat ceilings are an easy way to do so. See Figures 3.3b-c for some examples of good (and  bad) ceiling designs. Also not that “cathedral” or “A-frame” ceilings can be quite

helpful in live rooms. (They are generally discouraged in control rooms due to focusing effects.)

5.6

Walls

Unfortunately, the basic walls built in most homes and businesses are simply not dense enough or thick enough to be good barriers to neighboring sound. This page will show you proven methods for adding additional layers of materials to your existing walls to make the most of them. For those of you doing new construction, these tips are applicable as well. The choice of how to retrofit your existing walls, ceiling, etc. is entirely

up

to

you,

your

ears

and

your

pocketbook.

Existing Walls First, determine as best you can what the materials are which comprise your existing walls. You hope you find out that you have 2x6 walls, heavily insulated and caulked, floated on SheetBlok, then covered with a layer of ⅝" gypsum board, a

layer of SheetBlok, a layer of ½" gypsum board and surface treated with Studiofoam.

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If so, go directly to Park Place, collect $200 and have dinner at a fancy restaurant. If not, read on. If your problem sounds severe to you and you learn that the existing wall has no insulation in it, it is advisable to install Auralex Mineral Fiber in it by removing the gypsum board and  placing the Mineral Fiber between the wall studs. Alternatively, you can look into  blowing insulation into the wall with a machine (see your local hardware store for details). Having done that, the more closely you can retrofit your wall to resemble the one shown in Figure 3.5 above, the better off you will be. You can choose to alter materials or leave off layers, but the performance of the wall may be lessened, so delete or change at your own risk. Naturally, you should use good construction techniques, taping, mudding and caulking seams all the way, making sure to stagger all seams and rotate adjoining layers 90° from each other. If you determine your problem to be relatively minor, you might be able to get by with as little as adding one (1) more layer of gypsum board. If you previously found out your existing wall is one layer of ½" gypsum board or plaster on lathe (older homes), add a layer of SheetBlok and then another layer of ⅝" gypsum board. Do you want to go to the trouble to fur out from

your existing wall to hang your new wall boards on? We think so. It is neither a waste of time nor money and, if you have both, we would encourage it...but with a twist. At least cover the faces of the furring strips with strips of SheetBlok (it is considerably more effective to actually mount a layer of SheetBlok across the faces of the furring strips versus just putting strips of SheetBlok on the furring strips' faces, but it also costs more). Then mount RC8 across the furring strips. Then mount a layer of ⅝” gypsum  board to the channels. Construction If you have the opportunity to build your space taller, allowing for a false/lowered ceiling and giving your studio more cubic space, then you are indeed lucky. If that’s the case,   there are a few things to note that you might implement to improve on the wall/ceiling described above. • You should

definitely build a "room within a room," meaning that there is air space and no  physical contact between the exterior walls and the new walls of your studio! There is no substitute for doing it this way. You can build just one wall and can add layers to the wall until you are blue in the face and poor as Patty’s pig, but chances are that you

will never achieve the level of sound transmission control you will if you go the extra mile and build a room within a room. You know what they say about an ounce of  prevention being worth a pound of cure? In the practice of acoustics, an ounce of

53

 prevention is worth considerably more than a pound of cure. • Sound can slip through very tiny gaps (1/32” and smaller) which might seem to you

to be insignificant. So it is of extreme importance to construct your place as airtight as humanly possible. When humanly possible is not good enough, StopGap can be of great benefit. The specific gaps we are talking about here are, e.g., the gaps around electrical boxes (remove the outlet and switch plates to find them), underneath door trim, baseboard, crown-molding, around HVAC vents (remove the grilles to find them), and so on. This is all part of the attention to detail we’ve been talking about • Never mount electrical boxes or connector panels back to back; always stagger them

as shown in the Seal the holes your wires go through, or (preferably) run wire through conduit, stuffing foam or insulation in the ends to help seal it. Isolating the conduit from the structure with SheetBlok or hanging it with resilient hangers can really offer some improved isolation. Remember: Sound control is a game of inches. Of course, the less wires and boxes you have poking holes in your walls, the less chances sound has to get through where you do not want it. It may be prettier having all your boxes flush mounted, but there is a lot to be said for surface mounting your phone cables and jacks, audio connector boxes, light switches, etc. Not only does this method yield better isolation, your artsy friends might consider you "retro", "industrial" and just plain "cool." Studiofoam and other treatments applied to room surfaces can often mask surface-mounted goodies. • It is always better to keep wires away from each other than in big globs; especially

audio, video, data and phone lines that might be in proximity to electrical wires. If wires have to cross, doing so at a right angle lessens the chance of interference occurring. Otherwise, keep all the different types of wires at least 12” away from each other and use shielded cable wherever possible.

5.7

Doors

Isolation The best common doors to use are exterior grade, solid-core wood (“slab”) doors that are flat, without moldings. Also common, but more expensive, are commercial and/or exterior grade insulated steel doors. You can add SheetBlok to one or both sides of either type of door before installing the knob to provide additional transmission loss, then Studiofoam over the SheetBlok. If you have the inclination, you 54

can make a door sandwich out of two (2) solid-core doors and a couple layers of SheetBlok in the middle (this is the sort of thing Eddie Van Halen did at his 5150 studio). If you desire to have the ability to lock your door, be sure you can find a knob/lock that will work with your thicker-than-normal door. Double doors (backto back) are of some benefit if they are (a) attached to physically separate door jambs that are floated, and (b) are as far apart as possible given the constraints of your framing structure.

Build your walls and double doors in such a way as to give you as much dead air space between the doors as possible.Figure 4.1 shows methods of installing back-to back doors for single and double framed walls. Alternate your door knobs and hinges left to right. You can add surface moldings to your slab doors if you want to dress them up. Install Studiofoam on your doors  –   especially the sides that face each other. This absorbs any resonance that might occur between them. The biggest reason that doors are poor in the area of sound control often has little to do with the physical construction of the doors themselves (if you are using one of the types outlined above). The weakest link in most door systems is that they are not sealed well with the floor  below them or with the frame around them. You must use a compressed rubber threshold below your door and you must make sure that wherever the door shuts and would normally contact the door jamb it meets foam 2930 weatherstrip tape or a rubber

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gasket. Magnetic seals can also be used, like you would find on a refrigerator door. For those requiring the ultimate in door seals, you might contact Zero International. They specialize in door seals that do a fantastic job of blocking sound. If you are looking to save yourself a considerable amount of time (and headaches), you might consider simply specifying some sound-rated doors right into your studio. While they are expensive, sound-rated doors give you far superior performance to anything you could do with a single door on your own. Manufacturers of high-quality acoustical doors include:

• Industrial Acoustics Company • Overly Door and Window Company

At most, you can expect an STC-30 to 32 from even the best solid-core door. The best double-frame, back-to-back solid-core door arrangement rarely yields better than STC50. By contrast, typical single-leaf doors from the manufacturers above can yield ratings of STC-55 and higher. Worth considering if maximum sound isolation is your goal. Garage doors

The concept of the overlapping doors spoken of and diagrammed above is easily adapted to a solution for leaky garage doors, especially if you break down the solution into multiple "bi-fold" type doors that seal well where they meet. The better solution, however, is to build a false, floated wall next to the garage door that does not come into contact with it and is isolated as well as possible from the existing structure using the methods described . If your budget permits, placing a layer of SheetBlok over the interior face of the door before framing your new wall is advised. Most garage doors leak water, so you might want to raise the garage door the width of a 2x4 and then nail a treated, weather-resistant 2x4 under the garage door (floating the 2x4 with SheetBlok and sill seal, available at your hardware store) and caulking with StopGap where it meets the concrete, door frame, etc.). Having done that, lower the garage door down to it and nail up a 2x4 above the top interior edge of the garage door to keep it from being raised. You are then protected from water and thievery and everything you have done can easily be removed in the future should you or a subsequent property owner desire.

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Airlocks

Many of you will be building studios in your basement and sound traveling up your stairwell may prove to be a problem. If possible, enclose your stairway and put a good, solid-core door at the bottom to keep most of your sound out of the stairwell. In addition, or if enclosing the stairway just is not feasible, apply as much 4" Studiofoam in the stairwell as possible to absorb as much ambient sound as you can, thus making less sound available to travel upstairs. Stairwells tend to resonate quite a bit, so if you are enclosing and adding a door, do everything you can to float or at least really bulk up your new construction. If building an airlock or “sound -lock” (a small room

separating one sound-critical space from another and into which each of those rooms’ doors opens), float everything you can, use SheetBlok copiously and treat the walls and ceiling with the thickest Studiofoam you can afford. If you have the know-how to build a window into the door –   or you can afford a sound-rated door with a window built-in  –  this sound-lock can often serve as a vocal or isolation booth.

5.8

Windows

5.8.1

Exterior

Often, it is relatively easy to add in a second window if you are already building a second wall.If you are going to do this, i.e., install a second pane of plate, insulated, or laminated glass,make sure the panes are as far apart as possible, are parallel to each other,

and

never

touch

wood

framing

of

your

new

wall.

The windows should only come into contact with SheetBlok, foam weatherstrip tape (FrostKing 3/4" wide by 7/16" thick, closed-cell, heavy-duty, interior/exterior recommended) or StopGap. You can either route out grooves for the glass to fit it or just block it in with small wood 57

slats. Line the frame of the air space with Studiofoam to absorb standing waves and throw some packets of silica gel in between the panes to absorb the condensation that invariably forms there. See the Interior section below for more information. Clear SheetBlok™ in use at Perfect Sound Studios

Examples of exterior window isolation: 1. We recently helped drummer-extraordinaire, Kenny Aronoff, design and construct his new studio. Kenny had already purchased and installed some decent windows, but was concerned that they might not be as soundproof as he needed them to be. We sent a couple members of our Engineering department down to Kenny's place and were  pleasantly surprised when his testing showed that the windows were "soundproof enough.”

2. Around the same time, we helped Joe Kasko with his new facility, Perfect Sound Studios. (As it turns out, Joe is actually a friend of Kenny's. Small world!) When we were brought into the project, conventional windows had already been installed. They were not quite good enough to prevent sound from leaking out and bothering the neighbors behind the studio. In lieu of trashing the windows and losing the investment that had already been made, personnel devised –   and Joe implemented –   some "plugs" for the window openings using Clear SheetBlok, 1x3s and other materials. The results were great and our testing showed that they cut the level of sound transmission dramatically. When installed, the window plugs still afford the ability to see outside as shown in Figure 4.2. (But not perfectly because Clear SheetBlok is not as perfectly clear as glass). [Worth noting is that Perfect Sound Studios has implemented the full Auralex arsenal from construction products to absorbers and diffusers (some of the coolest painted T'Fusors we have seen). The place looks and sounds awesome ] 5.8.2

Interior

A double window between a control room and a studio is often used because single paned windows are very poor at stopping sound. You want to try to keep the panes  parallel to each other to maximize the dead air space between them and you do not want to use three panes because using three panes actually lessens the contiguous dead air space. If you must angle your glass, angle only one pane, 31not both, and make it a slight angle going up. Note that if you cannot angle the glass by at least 8°, you are  probably wasting your time anyway. No matter how you decide to construct your

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window, a good way to really clean your glass prior to installation is to mix 1 drop Ivory

dish

soap

gently

with

one

(1)

gallon

distilled

water.

Or just use a Windex -type glass cleaner. Do a good job because you are going to have to live with any smudges for a long, long time! Wearing cotton or rubber gloves while installing the glass is recommended. Figure 4.3 shows the preferred method of constructing your double-paned window. Make sure glass never touches wood and float the whole construction on SheetBlok to isolate it from your control room and studio walls. Throw a couple packets of silica gel into the dead air space to absorb unwanted moisture that could fog your windows. Line the inside perimeter of the dead air space with Studiofoam to help cut down on resonance. And just so we are all on the same page in terms of the different types of glass: • Plate glass is simply a solid piece of glass. This type of gla ss typically has the worst

 performance in terms of sound isolation. • Insulated glass is actually two (2) thin pieces of plate glass separated by an airspace.

There is an airtight frame around the glass and this type of glass is a pretty good  performer in terms of isolation. You can also find insulated glass that fills the space  between with an inert gas like argon. This does offer you an advantage since the speed of sound in argon is different from that of air. This is known as an impedance mismatch and can give you a slightly better STC. • Finally, the best glass performer, in terms of sound isolation, tends to be laminated

glass. Laminated glass is much like insulated glass, except in lieu of a airspace, there is a laminate  –   i.e., a clear glue. This is an even better impedance mismatch than that  provided by the insulated glass. We strongly encourage the use of laminated glass for any studio. A final note about glass block: Glass block is often desirable when natural light is welcome, but prying eyes are not. Glass block tends to be a great sound 59

 performer. There are typically two varieties: Solid block and hollow block. The neat thing is there is not much of a performance difference between the two because the hollow block is actually evacuated. This happens when the two pieces of glass are superheated to fuse them together and form the hollow block. The air trapped inside the cavity is also at thousands of degrees when the block is formed. As it cools, the volume of the cavity is constant, but the temperature drops considerably. When this happens, the pressure drops to next-to-nothing (Boyle’s Law for you propeller -heads), which we call, for all intents and purposes, a vacuum. Since sound cannot pass through a vacuum, this is very advantageous for sound control.

Chapter-6. Conclusion Acoustics has become a very important part of our building envelopes. The total urban scenario has resulted in increased noise levels in the surrounding which lead to discomfort in one’s own shelter. Acoustic design shall be made mandato ry for

architects and constructionists for comfortable living of dwellers. Both and active and  passive acoustical techniques and treatments ranging from minimal to economical to luxurious are available depending upon the monitory investments. Acoustics should not be ignored while designing a building but it shall lead the designer to a better place of living.

Chapter-7. References 

http://www.measuretronix.com/files/news/Section_3_-_Building_Acoustics.pdf



http://en.wikipedia.org/wiki/Architectural_acoustics



http://www.acoustictrade.com/pdf/acoustictrade_brochure.pdf



http://www.jeacoustics.com/library/pdf/ConSpec_Apr90_Concert_Halls.pdf



http://www.kineticsnoise.com/interiors/pdf/Interior2.pdf



http://www.acousticsfirst.com/



http://www.thefreedictionary.com/noise



http://www.acoustics.org/archacouintrotoot.pdf



http://ebookbrowse.com/architectural-acoustics-0311-pdf-d97024642 60



http://www.acoustics.com/project_remedies.asp

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