Chapter 5 Notes

CHAPTER 5: THE AUDITORY SYSTEM – SOUND AND EAR Audition: The detection of sound and and ability to determine determine its source source -

Essentia Essentiall for for loacin loacing g food, food, nding nding mates mates and avoiding avoiding predato predators. rs. Audition Audition is a distant distant sense sense – stimul stimulus us can can be detected detected from from far away away Auditi Audition on opera operatio tions ns at the the fas fastes testt time time scale scale

The Physics of Sound  Essenti!" Re#ui$e%ents to he!$ sound: -

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Some Someth thin ing g tha thatt cr create eates s the the soun sound d Soun Sound d must must pro propa paga gate te thr throu ough gh a med mediu ium m o ell !ar e"periment# the sound produced by a bell becomes les audible if enclosed in a $ar in which air is slowly pumped out %echanis %echanism m to transla translate te sound sound energy energy into biolo biologica gicall signal signal to gener generate ate the the e"perien e"perience ce &nown as hearing

The C$e!tion of Sound -

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'ibratio 'ib rational nal (rop (ropertie erties s of )b$ects# )b$ects# *nertia *nertia + Elastic Elasticity ity  'ib 'ibratio rations ns o *nertia – an ob$ect will initially resist deformation, but once started it will continue until an opposing force acts on it o Elasticity – The opposing force that brings an ob$ect to its original state o i.e. using a tuning fork , vibrations of the prongs will create a simple harmonic motion represented motion represented by a sinusoidal function. *mpact *mpact of a Sound Sound Source Source on the the %edium# %edium# ompre ompressio ssion n and rarefact rarefaction ion of of air o ompression– *ncreased air pressure pressure bc of prongs moving outward pushing against it o /arefaction – 0ecrease air pressure bc of prongs moving inwards leaving a space o Sound wave – created by the propagation of the momentary compression  rarefaction of air

The P$o&e$ties of Sound -

Ampl Amplit itud ude e and and Soun Sound d *nte *ntens nsit ity# y# o Amplitude – pressure change from the baseline to the highest pea& 1measure in (a or &(a2 *ncrease in loudness of sound  *ncrease in amplitude o *ntensity – a word used to describe the loudness of sound *ntensity of an ob$ection is considered in relation to a reference point Refe$ence &oint   the lowest sound level that can be heard 1345(a2 *ntensity is represented by Deci'e"s (d)*+ A log scale where 64d  6bel and 6bel  log1* s*r2 SP,  Sound pressure level. d)SP,  the reference value use to calculate intensity is the lowest sound level that can be heard Sound Sound 7re8 7re8uenc uency y# 9 of comple complete te cycles cycles  second. second. %easu %easured red in :ert; :ert; 1:;2 1:;2 o :umans can only hear between 34-3444 :; o N!tu$!" (Reson!nt* -$e#uency – fre8uency of an ob$ect due to its mass and sti6.?ms @ 4 in A*/ o Speed is entirely dependent on the characteristics of the medium – inertia and elasticity o *nertia 1density2 of medium is related to speed inversely – increase density decrease speed o  Temperature – *ncrease temp  increases speed *ncreasing temperature causes e"pansion of molecules  decreases density  increase speed 6 increase  4.Bms increase in speed of sound o Elasticity of medium is related to speed directly – increase elasticity  increase speed i.e. sound actually travesl 6B" faster in steel than air bc of elasticity o

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Co%&"e. Sounds /

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omple" (eriodic Sounds# Chen the pattern of pressure change repeats itself at regular intervals over time o *t does not have a sinusoidal function DT its formed by adding multiple sinusoidal function with di