Sound and the Ear
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Transcript of Sound and the Ear
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SOUND & THE EAR
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Anthony J Greene 2
Sound and the Ear1. Sound Waves
A. Frequency: Pitch, Pure Tone.
B. Intensity
C. Complex Waves and Harmonic Frequencies
2. The EarA. The Outer Ear
B. The Middle Ear
C. The Inner Eari. The Cochlear Membrane
ii. Sound Transduction
iii. Hearing Loss
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Anthony J Greene 3
Sound Waves
1. Frequency
• Wavelength - distance between peaks or compressions
• Hertz - cycles (1 compression & 1 rarefaction) per second - the major determinant of pitch
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Anthony J Greene 4
Sound Waves
• Pure Tones - simple waves
• Harmonics - complex waves consisting of combinations of pure tones (Fourier analysis) - the quality of tone or its timbre (i.e. the difference between a given note on a trumpet and the same note on a violin) is given by the harmonics
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Anthony J Greene 5
Sound Waves
• Pitch and fundamental frequency - in pure tones the pitch is the fundamental frequency - with harmonics added the fundamental frequency is the dominant pure tone
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Anthony J Greene 6
Sound Waves
2. Intensity• Amplitude is measured in Decibels (dB)-
the height of the peak, or the amount of compression - determines volume
• Loudness is the psychological aspect of sound related to perceived intensity or magnitude
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Anthony J Greene 7
Sound Waves• Humans can hear across a wide range of sound
intensities
– Ratio between faintest and loudest sounds is more than one to one million
– In order to describe differences in amplitude, sound levels are measured on a logarithmic scale, in units called decibels (dB)
– Relatively small decibel changes can correspond to large physical changes (e.g., increase of 6 dB corresponds to a doubling of the amount of pressure)
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Anthony J Greene 8
Sound Waves
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Anthony J Greene 9
Compression Rarefaction
Direction of Sound Air Molecules Speaker
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Anthony J Greene 10
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Anthony J Greene 11
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Anthony J Greene 12
Harmonics & Fourier Analysis
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Anthony J Greene 13
Harmonic Frequencies
• Strings or pipes (trombone, flute organ) all have resonant frequencies.
• They may vibrate at that frequency or some multiple of it
• All instruments and voices carry some harmonics and dampen others
Length of string or pipe
1f
2f1 octave
3f
4f2 octaves
8f3 octaves
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Anthony J Greene 14
Harmonic Frequencies
1f + 3f + 5f + 7f + 9f + …
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Anthony J Greene 15
Harmonics & Fourier Analysis
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Anthony J Greene 16
Harmonics & Fourier AnalysisComplex sounds can be described by Fourier analysis
A mathematical theorem by which any sound can be divided into a set of sine waves. Combining these sine waves will reproduce the original sound.
The fundamental frequency is the pitch, and the harmonic frequencies are the timbre.
Results can be summarized by a spectrum
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Anthony J Greene 17
Harmonics & Fourier Analysis
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Anthony J Greene 18
The Ear
Outer Ear Middle Inner Ear Ear
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Anthony J Greene 19
Outer Ear
• Pinna - the fleshy part of the ear
• Channels sound into the auditory canal - which carries the sound to the eardrum
• tympanic membrane - vibrates in response to vibrations in the air
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Anthony J Greene 20
Middle Ear• Ossicles - the three smallest bones in the
human body - malleus (hammer) incus (anvil ), stapes (stirrup ) - transmit sound to the inner ear
• Eustachian tubes - connects to throat and allows air to enter the middle ear - equalizes the pressure on both sides of the eardrum
Conduction Deafness
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Anthony J Greene 21
Inner Ear
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Anthony J Greene 22
Inner Ear
1. Semi-Circular Canals
2. The Cochlea• Oval Window -
the connection point from the stirrup to the inner ear
• Round Window
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Anthony J Greene 23
Inner Ear1. Semi-Circular
Canals2. The Cochlea• Oval Window -
the connection point from the stirrup to the inner ear
• Round Window
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Anthony J Greene 24
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The Cochlea• Vestibular canal - wave travels from the oval
window towards the end of the cochlea• Tympanic canal - wave travels from the end of the
cochlea to the round window• Reissner's Membrane - separates the vestibular canal
from the Cochlear Duct• Basilar membrane - vibrates in response to the wave
traveling around it - varies in thickness so some areas vibrate best to high pitches and some areas to low pitches
• Cochlear duct -the third section of the cochlea which contains the Organ of Corti
• Organ of Corti - the place where physical energy is converted to nerve energy
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Anthony J Greene 26
The Cochlea
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Anthony J Greene 27
The Cochlea
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Anthony J Greene 28
The Cochlea
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Anthony J Greene 29
Sound Transduction• A traveling wave is set up in the vestibular canal• The wave causes the Basilar membrane to vibrate
- each section is maximally stimulated by a different pitch - serves to sort out differing frequencies
• In the Organ of Corti hair cells vibrate in response to the vibrations of the Basilar membrane
• Hair cells transduce the energy into a neural impulse
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Anthony J Greene 30
Bassilar Membrane
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Anthony J Greene 31
Basilar Membrane
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Anthony J Greene 32
Exposure to Loud Noise
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Anthony J Greene 33
Summary