sound and auditory mechanics

impact loud speaker upon particle distribution in the air

sound amplitude depends on variation of sound pressure

modulation of atmospheric pressure = 100.000 Pascal

peff = (½ √2) pmax

hearing threshold = 0.00002 Pa

SPL (dB) = 20×log (p/pref)

reference 2.10-5 Pa

pref, 0 dB SPL

SPL = 20×log (p/pref)

when you double sound pressure, sound intensity increases with ?

when you double sound pressure, sound intensity increases with 6 dB

20 log p1/p2 = 20 log 2 = 20×0.3 = 6

Question

When two students talk non-synchroneously with a sound intensity of 60 dB SPL each, what do they produce together ?

Answer

When two students talk non-synchroneously with a sound intensity of 60 dB SPL each, they produce together 2 times more energy = 63 dB total

when you double sound pressure, sound intensity increases with 6 dB

20 log p1/p2 = 20 log 2 = 20×0.3 = 6

but energy increases with 3 dB

10 log e1/e2 = 10 log 2 = 10×0.3 = 3

Question

When two students talk synchroneously with a sound intensity of 60 dB SPL each, what do they produce together ?

Answer

When two students talk synchroneously with a sound intensity of 60 dB SPL each, they produce together 66 dB total

Question

What is the total sound intensity in a room with- A radio 70 dB SPL- Two students speaking asynchronous, each 60 dBSPL- one plane flying over with 80 dB SPL perceived in the room

Question

What is the total sound intensity in a room with- A radio 70 dB SPL- Two students speaking asynchronous, each 60 dBSPL- one plane with 80 dB SPL

First transfer into energies, then sum and transfer in dB again.Result = 80.1 dB

sound intensity decreases with r²

 Normal hearing threshold 1000Hz  0 dB SPL

 Falling leaves  10 dB SPL

 Whispering  20 dB SPL

 Very soft talking in a room  40 dB SPL

 Normal speact 1at 1 m  60 dB SPL

 Loud conservation with shouting  80 dB SPL

 Pneumatic hammer  100 dB SPL

 Disco  110 dB SPL

 Very loud sound speaker  120 dB SPL

 Starting airplane at 20 m.  130 à 140 dB SPL

 Pain threshold  130 à 140 dB SPL

resonance and impedance

auditory canal = open pipe

(1, 3, 5 enz.) x ¼

27 mm = ¼

(1, 3, 5 enz.) x ¼

27 mm = ¼

= 108 mm f = 3100 Hz

gehoorgang = open orgelpijp

resonantiegebied = 2000- 5000 Hz

transition air - liquid

acoustic impedance Z = p / u (in Rayleigh like Ohm)

p: pressure neededu: velocity

impedance endolympfe 56000impedance air = 410

factor 135: 97% reflection: therefore ossicles

resonance including ossicular chain: 1000 Hz

impedance

1. resistence: frequency independent transfer sound energy in heat

2. stifness= elasticity that decreases with frequency

3. inertia increases with frequency

compliance (in ml) = 1 / impedance

Hefboomwerking Middenoor

17x

1.3x 2x

17x1.3x2=44.2 pressure gain

10 log(44.22) = 33 dB theoretical gain

measured: ≤ 30 dB

function inner ear

- mechanical-electricial transition by the inner hair cells

- frequency analysis by macromechanics of the basilar membrane

- increasing sensitivity by micro-mechanics by the outer hair cells

Cochlear model

Ovale venster

Ronde venster

Helicotrema (verbindingScala vestibuli en Scalatympani)

http://www.iurc.montp.inserm.fr/cric/audition/start.htm

- mechanical-electricial transition by the inner hair cells tip link – Hudspeth spring model

- increasing sensitivity by micro-mechanics by the outer hair cells: the cochlear amplifier

- deflecion towards kinociulim decreases receptor potential results in: mechanical deformation of the cortical latticeleading to a shortening in cell body length and increase in diameter

moving the basilary membrane further away from the kinocilium

Mechanics outer hair cells + membrane: second resonator and cochlear amplifier

Animation : http://cc.usu.edu/~dgsinex/courses/SHS311_notes/2-ear/corti.htm

Efferent innervation: function selective hearing

Micro mechanics adds energy to the tranverse wave