Acoustics
Sound
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mechanical oscillation
20Hz - 20kHz – audible sound
0,7Hz - 20Hz – infrasound
20kHz – hundreds of MHz - ultrasound
Speed of sound
E … Young’s modulus of elasticity
(stell cca 5100 m/s)
K … volume stress modulus
(water cca 1500 m/s)
Rychlost šíření zvuku
Ambient
Speed of sound c (m/s)
Air 0°C
332
Air 20°C
344
Hydrogen
1270
Water 13°C
1441
Water 20°C
1484
Ice 0°C
3200
Rubber
1440
Steel
5000
Glass
6000
Speed of sound in air
Effect of temperature
tempetarute [°C]
ρ in kg·m-3
c in m·s-1
Z in N·s·m-3
−10
325.2
1.342
436.1
−5
328.3
1.317
432.0
0
331.3
1.292
428.4
5
334.3
1.269
424.3
10
337.3
1.247
420.6
15
340.3
1.225
416.8
20
343.2
1.204
413.2
25
346.1
1.184
409.8
30
349.0
1.165
406.3
Acoustic particle displacement,
speed and pressure
a = amax.sin (ω.t) = amax.sin (2π.f.t)
v = da/dt = amax.2π.f.cos (2π.f.t) = vmax.cos (2π.f.t)
pmax = ρ.c.vmax
Total pressure in one point: atmopheric pressure + acoustic pressure
Efective acoustic speed and pressure
vef = vmax/√2
pef = pmax/√2
pef = ρ.c.vef
Acoustic impedance
Analogy to el. parameters:
Z = Uef/Ief => Z = pef/vef
Z=c.ρ
Acoustic impedance is characteristic parameter for
Each ambient and affects quantum of acoustic energy
rebounded on transition between two ambient with
different acoustic impedance.
Sound intensity
I = P/S [W/m2]
I = ½ . pmax.vmax = ½ . vmax2.ρ.c = ½ . pmax2/(ρ.c)
I = pef.vef = vef2.ρ.c = pef2/(ρ.c)
Io = 10-12 W/m2
Sound intensity level
L(B)=log (I/Io) [B]
L(dB) = 10.log (I/Io) [dB]
L(dB) = 10.log (I/Io) = 10.log (pef/po)2 =
= 20.log (pef/po)
p0 = 2.10-5 Pa
Acoustic pressure in sound
Source of sound
Theoretical limit for undistorted sound at
Sound pressure
Sound pressure level[6]
pascal
dB re 20 μPa
101,325 Pa
194.0937 dB
Krakatoa explosion at 100 miles (160 km) in air
20,000 Pa
[2] 180 dB
Simple open-ended thermoacoustic device [7]
12,000 Pa
176 dB
5,000 Pa
168 dB
Jet engine at 30 m
630 Pa
150 dB
Rifle being fired at 1 m
200 Pa
140 dB
Threshold of pain
100 Pa
130 dB
20 Pa
approx. 120 dB
6 – 200 Pa
110 – 140 dB
2 Pa
approx. 100 dB
6×10−1 Pa
approx. 85 dB
Major road at 10 m
2×10−1 – 6×10−1 Pa
80 – 90 dB
Passenger car at 10 m
2×10−2 – 2×10−1 Pa
60 – 80 dB
2×10−2 Pa
approx. 60 dB
Normal talking at 1 m
2×10−3 – 2×10−2 Pa
40 – 60 dB
Very calm room
2×10−4 – 6×10−4 Pa
20 – 30 dB
Leaves rustling, calm breathing
6×10−5 Pa
10 dB
Auditory threshold at 2 kHz
2×10−5 Pa
0 dB
M1 Garand being fired at 1 m
Hearing damage (due to short-term exposure)
Jet at 100 m
Jack hammer at 1 m
Hearing damage (due to long-term exposure)
TV (set at home level) at 1 m
Ear
Outer ear
 Lobe – gristle (direction of acoustic
oscillation to ear canal)
 Ear canal – gristle and bone, 3cm
(sound -> tymapnum)
 Ear drum – tissue membrane, 0,1mm
Middle ear
 Air filled antrum
 Earbones
 Malleus
 Ambos
 Stapes
 Eustachian tube – pressure balancing
Internal ear
 Cochlea– liquid filled
 Corti’s organ
 Hair cells
 Audible nerve
Auditory field
Loudness level
Weighted filters
Hearing disorders
 Conductive hearing
 Otitis
 Otosclerosis
 Sensorineural loss
 Menier’s disease
 Neurinom
Diagnostics methodes
 Audiometry
Kochlear reserve
Tone audiometry: conductive hearing on right side
Tone audiometry: sensorineural loss on left side
Kochlear reserve
Tone audiometry: mixed loss on left side
Diagnostics methods
 Tympanometry
 Diagnostic of middle ear
Umožňuje vyšetřit:
 Reflexies:
 m.stapedius
 m.tensor tympani
 Decay test
 Volume:
 ear canal (only with undemaged ear drum)
 ear canal and mastoideal chambers (
perforated ear drum)
Tympanometry:
curve A = physiological status
Tympanometry:
curve C = dysfunction of ET
Tympanometry:
curve B = high rigidity
(liquid in middle ear –
myringosclerosis…)
Diagnostics methods
 Otoacoustic emission
 Spontaneous (SOAEs)
 Evoke (tone, broad frequency spectrum)
 For internal ear
 For newborn
Hearing compensation
 Hearing aid
Hearing compensation
 Cochlear neuroprotesis
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Microfon
Speech processor
Transmitter
Receiver
Stimulator
Electrodes