Acoustics
Sound 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 zvukuAmbient Speed of sound c (m/s)Air 0°C 332Air 20°C 344Hydrogen 1270Water 13°C 1441Water 20°C 1484Ice 0°C 3200Rubber 1440Steel 5000Glass 6000
Speed of sound in airEffect of temperature
tempetarute [°C] c in m·s-1 ρ in kg·m-3 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 impedanceAnalogy 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 intensityI = P/S [W/m2]
I = ½ . pmax.vmax = ½ . vmax2.ρ.c = ½ . pmax
2/(ρ.c)
I = pef.vef = vef2.ρ.c = pef
2/(ρ.c)
Io = 10-12 W/m2
Sound intensity levelL(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 soundSource of sound Sound pressure Sound pressure level[6]
pascal dB re 20 μPa
Theoretical limit for undistorted sound at 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
M1 Garand being fired at 1 m 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
Hearing damage (due to short-term exposure) 20 Pa approx. 120 dB
Jet at 100 m 6 – 200 Pa 110 – 140 dB
Jack hammer at 1 m 2 Pa approx. 100 dB
Hearing damage (due to long-term exposure) 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
TV (set at home level) at 1 m 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
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
Hearing disorders Conductive hearing
Otitis Otosclerosis
Sensorineural loss Menier’s disease Neurinom
Diagnostics methodes Audiometry
Tone audiometry: conductive hearing on right side
Kochlear reserve
Tone audiometry: sensorineural loss on left side
Tone audiometry: mixed loss on left side
Kochlear reserve
Diagnostics methods Tympanometry
Diagnostic of middle earUmožňuje 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
Microfon Speech processor Transmitter Receiver Stimulator Electrodes