### Cochlear mechanics

```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 ?
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 ?
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
-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
gehoorgang = open orgelpijp
(1, 3, 5 enz.) x ¼
27 mm = ¼
= 108 mm
f = 3100 Hz
resonantiegebied = 2000- 5000 Hz
transition air - liquid
acoustic impedance Z = p / u (in Rayleigh like Ohm)
p: pressure needed
u: velocity
impedance endolympfe 56000
impedance 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
Helicotrema (verbinding
Scala vestibuli en Scala
tympani)
http://www.iurc.montp.inserm.fr/cric/audition/start.htm
Ronde venster
- 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 lattice
leading 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
```