How Does the Ear Work

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How Does the Ear Work?
Animation 1
Animation 2
Animation 3
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How Does Sound Travel?

• Sound is produced by a vibrating source.
• Sound is a longitudinal, mechanical wave.
• Sound requires a medium through which to travel.

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How Does Sound Travel?

• Sound waves are transferred through a medium from
  particle to particle.
• The particles, vibrate back and forth, but do not
  move with the wave.
• Energy is transferred through the particles.
• Much like dominoes falling.

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How Does Sound Travel?

• The medium does NOT move with the sound wave
  only the energy moves.
• Look at the longitudinal wave below.
• Particles appear to be moving, but look closely,
  they are simply vibrating back and forth.

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Parts of a Sound Wave

• Compression
• Pulse of compressed matter, high pressure region.
• Rarefaction
• Disturbance in matter where pressure is lowered.

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Transverse Wave on Website
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Frequency

• Determined by rate at which source vibrates.
• A higher frequency of vibration produces a higher
  pitch.
• Pitch is the subjective impression of how high or
  low a sound appears to be.

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Frequency

• Young people can hear frequencies between
  20-20,000Hz
• As you age, your ability to hear high frequency
  sound decreases.
• You cannot hear waves outside of this range
• Infrasonic frequencies below 20Hz
• Ultrasonic frequencies above 20,000Hz
• Dogs can hear frequencies that range from
  67-45,000Hz

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Applications

• Ultrasound
• Animation 1
• Animation 2
• Sonar
• SOund Navigation And Ranging
• Website
• Radar (uses electromagnetic, not
  sound waves)
• RAdio Detection And Ranging
• Website

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Stealth Technology

• Airplane shaped so radar reflects away from radar
  equipment.
• Cover in material that absorbs radar signals

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Media That Transmit Sound

• Sound waves can travel through solids, liquids,
  or gases.
• The speed of sound depends on the medium through
  which it travels.
• Fastest in solids, then
• liquids, slowest in gases.
• 15x faster in steel than air
• 4x faster in water than air

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Speed of Sound

• Also depends on properties of the medium
• temperature
• elasticity
• ability of a material to change shape in response
  to an applied force and resume initial shape once
  distorting force is removed.

Sound waves used to determine depth of water?
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Speed of Sound in Air

• At 00C, sound travels at 330m/s.
• For every increase of 10C, the speed of sound
  increases by 0.6m/s
• V 330m/s (0.6m/s)T
• Warm air contains more
  humidity and faster
  moving molecules

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Speed of Sound Examples

• What is the speed of sound when the temperature
  is
• 500C
• 250C
• -150C
• 980C

? 360m/s
? 345m/s
? 321m/s
? 388.8m/s
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Decibels

• Sound level is measured in units of Decibels (dB)
• This is a logarithmic scale.
• An increase of 10dB represents a ten-fold
  increase in sound intensity.
• Each increase in loudness represents what change
  in intensity?
• 10dB
• 30dB
• 50dB
• -20dB

?10x
?1,000x
?100,000x
?.01x
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How Loud Is It?

• Loudness is determined by the amplitude
  of a wave.
• Loudness is described using the term intensity.
• Intensity
• The physiological perception of sound as sensed
  by the brain this differs from person to person.

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Common Sources of Sound

• Jet Engine 140dB
• Threshold of pain 120dB
• Loud Rock Music 110dB
• Subway Train 100dB
• Busy Street Traffic 70dB

• Normal Speech 60dB
• Library 40dB
• Close Whisper 20dB
• Normal Breathing 10dB
• Hearing Threshold 0dB

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Effect of Frequency On Perception of Loudness
Effect of frequency on perceived loudness
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Forced Vibration

• One object made to vibrate by sound waves
  produced by another vibrating object near by or
  in contact.
• Sounding board of musical instrument
• guitar, violin, tuning fork on table

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Natural Frequency

• The frequency at which an elastic object, once
  energized, will vibrate.
• Resonant Frequency.
• Every object has a natural frequency.
• Depends on
• elasticity
• shape of object

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Resonance

• When the frequency of forced vibrations on an
  object matches the objects natural frequency, a
  dramatic increase in amplitude results.
• resound, sound again
• Examples
• pumping/pushing a swing
• radio
• Tacoma Narrows Bridge

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Resonance

• In order to resonate, an object must be
  elasticable to vibrate.
• There must be enough force to pull the object
  back to the starting position and enough energy
  to keep it vibrating.

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Interference

• Types
• Constructive
• Destructive
• Results/uses
• Dead spots
• Anti-noise devices/
  noise cancellation
• Beats

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Beats

• Throbbing variation in loudness of sound caused
  by interference when two tones of slightly
  different frequencies are sounded together.

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Beats

• Produces a tremolo effect
• Beat frequency is equal to the difference between
  the two frequencies being combined.
• If a 440Hz and a 445Hz tuning fork are sounded
  together, what will be the beat frequency?

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Doppler Effect

• The change in frequency of a wave due to relative
  motion between the source and the receiver.
• Link to Doppler Animation 1
• Link to Doppler Animation 2
• Link to Doppler Animation 3

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Doppler Effect

• As the source of a sound moves towards you, the
  perceived frequency is greater than the actual
  frequency
• Each successive crest has a shorter distance to
  travel because the source moves forward between
  crests.
• Waves arrive at your ear more frequently than if
  they were emitted by a stationary source.

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Doppler Effect

• As the source of a sound moves away from you, the
  perceived frequency is less than the actual
  frequency
• Each successive crest has a longer distance to
  travel because the source moves back between
  crests.
• Waves arrive at your ear less frequently than if
  they were emitted by a stationary source.

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Doppler Effect
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Doppler Effect