Acoustics

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Acoustics
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Sound

• mechanical oscillation
• 20Hz - 20kHz audible sound
• below 20Hz infrasound
• above 20kHz ultrasound

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Speed of sound

• E Youngs modulus of elasticity
• (steel approx. 5100 m/s)
• K volume stress modulus
• (water approx. 1500 m/s)

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Speed of sound in various media
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Speed of sound in air
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Acoustic particle displacement, speed and pressure
a amax.sin (?.t) amax.sin (2p.f.t) v da/dt
amax.2p.f.cos (2p.f.t) vmax.cos
(2p.f.t) pmax ?.c.vmax Total pressure in
one point atmopheric pressure acoustic pressure
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Effective (RMS) acoustic speed and pressure
vef vmax/v2 pef pmax/v2 pef ?.c.vef
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Acoustic impedance
Analogy to el. parameters Z Uef/Ief gt Z
pef/vef Z c . ? Acoustic impedance is
characteristic parameter for each ambient and
affects quantum of acoustic energy rebounded on
transition between two ambient with different
acoustic impedance.
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Sound intensity
I P/S W/m2 I ½ . pmax.vmax ½ . vmax2.?.c
½ . pmax2/(?.c) I pef.vef vef2.?.c
pef2/(?.c) Io 10-12 W/m2
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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
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Acoustic pressure in sound
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Ear
Incus
Malleus
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Outer ear

• Lobe gristle (direction of acoustic oscillation
  to ear canal)
• Ear canal gristle and bone, 3cm (sound -gt
  tympanum)
• Ear drum (tympanic membrane) tissue membrane,
  thickness 0.1mm, area 50-90 mm2

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Middle ear

• Air filled antrum
• Earbones
• Malleus
• Incus
• Stapes (area 3 mm2)
• Eustachian tube pressure balancing

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Inner ear

• Cochlea liquid filled (perilymph)
• Cortis organ
• Hair cells (25000)
• Audible nerve

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Auditory field
threshold of pain
acoustic pressure dB
auditory field
threshold of hearing
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Loudness level
Loudness level Ph
Acoustic pressure level dB
FrequencyHz
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Weighted filters
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Hearing disorders

• Conductive hearing
• Otitis
• Otosclerosis
• Sensorineural loss
• Meniers disease
• Neurinom

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Diagnostics methodes

• Audiometry

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Kochlear reserve
Tone audiometry conductive hearing on right side
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Tone audiometry sensorineural loss on left side
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Kochlear reserve
Tone audiometry mixed loss on left side
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Diagnostics methods

• Tympanometry
• Diagnostic of middle ear
• Enables to examine
• Reflexes
• m.stapedius
• m.tensor tympani
• Decay test
• Volume
• ear canal (only with undemaged ear drum)
• ear canal and mastoideal chambers ( perforated
  ear drum)

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Tympanometry curve A physiological status
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Tympanometry curve C dysfunction of ET
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Tympanometry curve B high rigidity (liquid
in middle ear myringosclerosis)
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Diagnostics methods

• Otoacoustic emission
• Spontaneous (SOAEs)
• Evoke (tone, broad frequency spectrum)
• For internal ear
• For newborn

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Hearing compensation

• Hearing aid

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Hearing compensation

• Cochlear neuroprotesis
• Microphone
• Speech processor
• Transmitter
• Receiver
• Stimulator
• Electrodes