Hearing Mechanism <ul><li>Extremely sensitive microphone with selective frequency analysis </li></ul><ul><li>Detects parti...
 
Outer Ear <ul><li>Auditory canal: 0.7 to 2.5 cm in length </li></ul><ul><li>Behaves like a pipe closed at one end with an ...
 
Middle Ear <ul><li>Three supported bones: hammer, incus and stapes </li></ul><ul><li>Transfers vibrations from drum membra...
<ul><li>Volume 1-2 cc </li></ul><ul><li>Natural frequency of vibration 800 -1500 Hz </li></ul><ul><li>Dampens prolonged tr...
Inner Ear <ul><li>Comprises the vestibule, semicircular canal and cochlea </li></ul><ul><li>Vestibule connects the middle ...
Thresholds of the Ear <ul><li>Barely detected acoustic intensity at any particular frequency </li></ul><ul><li>Other: age ...
 
<ul><li>Greatest variation between listeners is observed over 30 yrs of age at higher frequencies </li></ul><ul><li>Age in...
<ul><li>Intensity of ~120 dB produces a tickling sensation </li></ul><ul><li>Prolonged exposure to 120 dB causes permanent...
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Acoustics of the Ear: The Hearing Mechanism

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Acoustics of the Ear: The Hearing Mechanism

  1. 1. Hearing Mechanism <ul><li>Extremely sensitive microphone with selective frequency analysis </li></ul><ul><li>Detects particular frequencies in backgrounds of wide band noise </li></ul><ul><li>Continuous band pass filter </li></ul>
  2. 3. Outer Ear <ul><li>Auditory canal: 0.7 to 2.5 cm in length </li></ul><ul><li>Behaves like a pipe closed at one end with an end correction of 0.85 times the radius </li></ul><ul><li>Resonance at 343m/s is 3kHz </li></ul><ul><li>At resonance pressure at drum membrane is about 10 dB higher than at the Pinna </li></ul><ul><li>Wide resonance curve: appreciable gain between 2-6kHz diffraction being taken into account </li></ul>
  3. 5. Middle Ear <ul><li>Three supported bones: hammer, incus and stapes </li></ul><ul><li>Transfers vibrations from drum membrane to the footplate of stapes that covers the oval window </li></ul><ul><li>Oval window connects middle ear and inner ear </li></ul><ul><li>Footplate oscillates and transmits pressure waves to the liquid filling of inner ear </li></ul><ul><li>Eustachian tube (normally closed) maintains pressure equilibrium between middle and outer ear </li></ul>
  4. 6. <ul><li>Volume 1-2 cc </li></ul><ul><li>Natural frequency of vibration 800 -1500 Hz </li></ul><ul><li>Dampens prolonged transient vibrations </li></ul><ul><li>Drum membrane area to oval window area ratio 30:1 </li></ul><ul><li>The ratio in conjunction with bone linkages provides necessary impedance matching between auditory canal (air) and the inner ear liquid filled </li></ul>
  5. 7. Inner Ear <ul><li>Comprises the vestibule, semicircular canal and cochlea </li></ul><ul><li>Vestibule connects the middle ear with the inner ear through two sealed windows - the oval window and the round window </li></ul><ul><li>Semicircular canals have no auditory function – instead they maintain a sense of balance </li></ul><ul><li>Cochlea is a wound structure with a roughly circular cross section 3.1 cm long with a 1.55 mm diameter </li></ul>
  6. 8. Thresholds of the Ear <ul><li>Barely detected acoustic intensity at any particular frequency </li></ul><ul><li>Other: age of the subject, direction of incidence </li></ul><ul><li>Resonance ~3000 Hz; 0 dB at 1 KHz; rises regularly with decreasing and rapidly with increasing frequency </li></ul><ul><li>Power required at 50 Hz is about 10 6 times that required at 300 Hz </li></ul>
  7. 10. <ul><li>Greatest variation between listeners is observed over 30 yrs of age at higher frequencies </li></ul><ul><li>Age independent below 1 kHz </li></ul><ul><li>Minimum perceptible pressures between 1-5 kHz are 2x10- 4 microbar </li></ul><ul><li>Amplitude of vibration of drum membrane is 10 -9 cm </li></ul>
  8. 11. <ul><li>Intensity of ~120 dB produces a tickling sensation </li></ul><ul><li>Prolonged exposure to 120 dB causes permanent damage </li></ul><ul><li>Tickling sensation graduates into a sensation of pain at 140 dB </li></ul><ul><li>Immediate damage is caused when > 160 dB </li></ul>

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