PHY2011 Lecture 15: Week 6 L1 (T4aL2) -Hearing
20 Jun 2018
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Week 6 L1 (No Wk5L3 b/c good Friday) (T4aL2) -Hearing
Sound
oa wave of pressure travelling through an elastic medium (air/water) by mechanical
disturbance (vibration) of molecules of the medium
othe speed of sound depends on the elasticity and density of the medium
air: 340m/s
water: 1500m/s
Tones
oPure tone =sine wave
oDefined by:
Frequency (pitch) -number of cycles per unit time (Hertz = cycles per sec)
- Humans: 20Hz to 20kHz
Amplitude (loudness) -size of pressure variations (SPL (sound pressure
variation) in Pascals (Pa))
- Decibel measure of SPL (dB)
- Humans: -10dB to 120dB
- Note: 0dB means there is no change in pressure, not that there is no
sound
Structures of the peripheral auditory system
oStimulus acts directly on receptor cells to cause the opening of ion channels
oPath of sound to the inner ear:
External ear canal eardrum malleus incus stapes cochlea
oMiddle ear: air filled cavity behind ear drum
Contains Ossicles and Eustachian tube
oCochlea: bony, fluid filled structure with two “windows”
Holes that enable the stapes to push into the cochlea and transmit the
pressure difference to the liquid
Windows are covered by membranes
find more resources at oneclass.com
find more resources at oneclass.com
oExternal and middle ear are accessories that help get sound energy to cochlea
efficiently
External ear:
oCone shape -funnels sound waves into ear
oFolds and irregular shape – modifies sounds to help identify directionality
(front/behind us)
Middle ear -amplifies sound
oMovement of the eardrum causes movement in each of the three middle ear bones
respectively
oStaples then pushes into the fluid, which causes you to hear sound
oWhy not remove all these structures and let the pressure move the fluid? Because it
is easier to compress air particles than fluid particles -not as efficient
oHow does the amplification happen?
1. Area of Tympanum > area of stapes foot plate
- Apply force on a larger area and forcing it upon a smaller area (Pin
vs thumb tac)
2. The ossicles move like a lever
- Small movement in one end causes a large movement in the other
end
The eardrum vibrates in a complex fashion
- Doesn’t just move like a plate
oEar wax and water reduce amplification because it’s harder for pressure to move
through these mediums before they get amplified by the middle ear structures
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Week 6 l1 (no wk5l3 b/c good friday) (t4al2) -hearing. Sound: a wave of pressure travelling through an elastic medium (air/water) by mechanical disturbance (vibration) of molecules of the medium, the speed of sound depends on the elasticity and density of the medium air: 340m/s. Tones: pure tone =sine wave, defined by: Frequency (pitch) -number of cycles per unit time (hertz = cycles per sec) Amplitude (loudness) -size of pressure variations (spl (sound pressure variation) in pascals (pa)) Note: 0db means there is no change in pressure, not that there is no sound. Structures of the peripheral auditory system: stimulus acts directly on receptor cells to cause the opening of ion channels, path of sound to the inner ear: External ear canal eardrum malleus incus stapes cochlea: middle ear: air filled cavity behind ear drum. Contains ossicles and eustachian tube: cochlea: bony, fluid filled structure with two windows .
