SOUND & THE EAR. Anthony J Greene2 Sound and the Ear 1.Sound Waves A.Frequency: Pitch, Pure Tone. B.Intensity C.Complex Waves and Harmonic Frequencies.

SOUND & THE EAR

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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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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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Compression Rarefaction

Direction of Sound Air Molecules Speaker

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Harmonics & Fourier Analysis

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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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Harmonic Frequencies

1f + 3f + 5f + 7f + 9f + …

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Harmonics & Fourier Analysis

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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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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. Semi-Circular Canals

2. The Cochlea• Oval Window -

the connection point from the stirrup to the inner ear

• Round Window

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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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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