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Acoustics

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  1. Acoustics

  2. Sound • mechanical oscillation • 20Hz - 20kHz – audible sound • 0,7Hz - 20Hz – infrasound • 20kHz – hundreds of MHz- ultrasound

  3. Speed of sound E … Young’s modulus of elasticity (stell cca 5100 m/s) K … volume stress modulus (water cca 1500 m/s)

  4. Rychlost šíření zvuku

  5. Speed of sound in air

  6. 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 + acousticpressure

  7. Efective acousticspeed andpressure vef = vmax/√2 pef = pmax/√2 pef = ρ.c.vef

  8. Acoustic impedance Analogyto el. parameters: Z = Uef/Ief=> Z = pef/vef Z = c . ρ Acoustic impedance is characteristic parameter for Each ambient andaffectsquantum of acoustic energy rebounded on transition between two ambient with different acoustic impedance.

  9. 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

  10. 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

  11. Acoustic pressure in sound

  12. Ear

  13. Outer ear • Lobe – gristle (direction of acoustic oscillationtoear canal) • Ear canal – gristle andbone, 3cm (sound->tymapnum) • Ear drum – tissue membrane, 0,1mm

  14. Middle ear • Air filled antrum • Earbones • Malleus • Ambos • Stapes • Eustachian tube – pressure balancing

  15. Internal ear • Cochlea– liquid filled • Corti’s organ • Hair cells • Audible nerve

  16. Auditory field

  17. Loudness level

  18. Weighted filters

  19. Hearing disorders • Conductivehearing • Otitis • Otosclerosis • Sensorineural loss • Menier’sdisease • Neurinom

  20. Diagnostics methodes • Audiometry

  21. Kochlear reserve Tone audiometry: conductive hearing on right side

  22. Tone audiometry: sensorineural loss on leftside

  23. Kochlear reserve Tone audiometry: mixedlosson left side

  24. Diagnostics methods • Tympanometry • Diagnostic of middle ear Umožňuje vyšetřit: • Reflexies: • m.stapedius • m.tensor tympani • Decay test • Volume: • ear canal (only with undemagedear drum) • ear canal and mastoideal chambers ( perforatedear drum)

  25. Tympanometry: curve A = physiologicalstatus

  26. Tympanometry: curve C = dysfunction of ET

  27. Tympanometry: curve B = highrigidity (liquid in middle ear – myringosclerosis…)

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

  29. Hearing compensation • Hearing aid

  30. Hearing compensation • Cochlear neuroprotesis • Microfon • Speech processor • Transmitter • Receiver • Stimulator • Electrodes