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 zvuku AmbientSpeed of sound c (m/s) Air 0°C332 Air 20°C344 Hydrogen1270 Water 13°C1441 Water 20°C1484 Ice 0°C3200 Rubber1440 Steel5000 Glass6000

Speed of sound in air Effect of temperature tempetarute [°C]c in m·s-1ρ in kg·m-3Z in N·s·m-3 − −

Acoustic particle displacement, speed and pressure a = a max.sin (ω.t) = a max.sin (2π.f.t) v = da/dt = a max. 2π.f.cos (2π.f.t) = v max.cos (2π.f.t) p max = ρ.c.v max Total pressure in one point: atmopheric pressure + acoustic pressure

Efective acoustic speed and pressure v ef = v max /√2 p ef = p max /√2 p ef = ρ.c.v ef

Acoustic impedance Analogy to el. parameters: Z = U ef /I ef => Z = p ef /v ef 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/m 2 ] I = ½. p max.v max = ½. v max 2.ρ.c = ½. p max 2 /(ρ.c) I = p ef.v ef = v ef 2.ρ.c = p ef 2 /(ρ.c) I o = W/m 2

Sound intensity level L (B) =log (I/I o ) [B] L( dB ) = 10.log (I/I o ) [dB] L( dB ) = 10.log (I/I o ) = 10.log (p ef /p o ) 2 = = 20.log (p ef /p o ) p 0 = Pa

Acoustic pressure in sound Source of soundSound pressureSound pressure level[6] pascaldB re 20 μPa Theoretical limit for undistorted sound at101,325 Pa dB Krakatoa explosion at 100 miles (160 km) in air20,000 Pa[2] 180 dB Simple open-ended thermoacoustic device [7] 12,000 Pa176 dB M1 Garand being fired at 1 m5,000 Pa168 dB Jet engine at 30 m630 Pa150 dB Rifle being fired at 1 m200 Pa140 dB Threshold of pain100 Pa130 dB Hearing damage (due to short-term exposure)20 Paapprox. 120 dB Jet at 100 m6 – 200 Pa110 – 140 dB Jack hammer at 1 m2 Paapprox. 100 dB Hearing damage (due to long-term exposure)6×10 −1 Paapprox. 85 dB Major road at 10 m2×10 −1 – 6×10 −1 Pa80 – 90 dB Passenger car at 10 m2×10 −2 – 2×10 −1 Pa60 – 80 dB TV (set at home level) at 1 m2×10 −2 Paapprox. 60 dB Normal talking at 1 m2×10 −3 – 2×10 −2 Pa40 – 60 dB Very calm room2×10 −4 – 6×10 −4 Pa20 – 30 dB Leaves rustling, calm breathing6×10 −5 Pa10 dB Auditory threshold at 2 kHz2×10 −5 Pa0 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 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 Microfon Speech processor Transmitter Receiver Stimulator Electrodes