Transcript 09 Sound And The Ear

SOUND & THE EAR
Sound and the Ear
1. Sound Waves
A. Frequency: Pitch, Pure Tone.
B. Intensity
C. Complex Waves and Harmonic Frequencies
2. The Ear
A. The Outer Ear
B. The Middle Ear
C. The Inner Ear
i. The Cochlear Membrane
ii. Sound Transduction
iii. Hearing Loss Anthony J Greene
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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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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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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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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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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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Sound Waves
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Direction of Sound
Air Molecules
Speaker
Compression
Rarefaction
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Harmonics & Fourier Analysis
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Harmonic Frequencies
1f
• 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
2f
1 octave
3f
4f
2 octaves
8f
3 octaves
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Length of string or pipe
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Harmonic Frequencies
1f
+
3f
+
5f
+
7f
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9f
+ …
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Harmonics & Fourier Analysis
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Harmonics & Fourier Analysis
Complex 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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Harmonics & Fourier Analysis
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The
Ear
Outer Ear
Middle Inner Ear
Ear
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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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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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Inner Ear
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Inner Ear
1.
2.
•
•
Semi-Circular
Canals
The Cochlea
Oval Window the connection
point from the
stirrup to the
inner ear
Round Window
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Inner Ear
1.
2.
•
•
Semi-Circular
Canals
The Cochlea
Oval Window the connection
point from the
stirrup to the
inner ear
Round Window
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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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The Cochlea
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The Cochlea
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The Cochlea
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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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Bassilar
Membrane
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Basilar Membrane
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Exposure to Loud Noise
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Summary
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