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 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 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 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 . pmax

2/(ρ.c)

I = pef.vef = vef2.ρ.c = pef

2/(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 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

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

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