SOUND

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SOUND
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ORIGIN OF SOUND

• Vibrations of a material object
• Guitar string
• Reed
• Column of air
• Vocal chords

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Origin of Sound

• Original vibration will then stimulate something
  larger
• Sounding board of guitar

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Origin of Sound

• Original vibration will then stimulate something
  larger
• Air column within reed
• or wind instrument

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Origin of Sound

• Original vibration will then stimulate something
  larger
• Air in throat mouth of singer

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Origin of Sound

• Frequency of vibrating source equals frequency of
  sound waves produced
• Frequency of sound is called pitch

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Origin of Sound

• On average most people can hear pitches that
  range in frequency from
• 20,000 Hz
• 20 Hz

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Origin of Sound

• On average most people can hear pitches that
  range in frequency from
• 20 Hz - 20,000Hz
• As we grow older that range shrinks

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Origin of Sound

• Infrasonic
• below 20 Hz
• Ex Elephants communicate
• in this range
  
• Ultrasonic
• above 20,000Hz
• Ex Bats communicate or hunt in this range
• Super Sonic
• does not refer to pitch but rather speed faster
  than sound

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Origin of Sound

• Infrasonic
• Ultrasonic
• Super Sonic
• Sonic Boom when an object travels faster than
  sound there is a sudden change of high low
  pressures

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Doppler Effect

• Change in pitch due to motion of the source or
  receiver
• Pitch goes up as sound moves toward you
• Pitch goes down as sound moves away from you

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Doppler Effect

• Change in pitch due to motion of the source or
  receiver
• Analogy is a bug disturbing the water

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Doppler Effect

• Change in pitch due to motion of the source or
  receiver
• Analogy is a bug disturbing the water

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Doppler Effect

• Change in pitch due to motion of the source or
  receiver
• Pitch goes up as sound moves toward you
• Pitch goes down as sound moves away from you

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Doppler Effect

• Change in pitch due to motion of the source or
  receiver
• Police use radar which can calculate the speed of
  a car by measuring the Doppler effect

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Doppler Effect

• Doppler Effect of Light
• Astronomers use the Doppler shift to gather data
  about heavenly bodies

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Doppler Effect

• Doppler Effect of Light
• Blue shift increasing frequency in visible
  light which indicates star motion as moving
  toward

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Doppler Effect

• Doppler Effect of Light
• Red shift decreasing frequency in visible light
  which indicates star motion is moving away
• A red shift in all galaxies reveals an expanding
  universe
• Spinning galaxies have red shift on side moving
  away blue shift on side moving toward

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Sound in Air

• Vibrations are sent to the surrounding as
  Longitudinal Waves

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Sound in Air

• Vibrations are sent to the surrounding as
  Longitudinal Waves

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Sound in Air

• Vibrations are sent to the surrounding as
  Longitudinal Waves

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Sound in Air

• Vibrations are sent to the surrounding as
  Longitudinal Waves

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Sound in Air

• Vibrations are sent to the surrounding as
  Longitudinal Waves

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Sound in Air

• Vibrations are sent to the surrounding as
  Longitudinal Waves

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Sound in Air

• Vibrations are sent to the surrounding as
  Longitudinal Waves

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Sound in Air

• Vibrations are sent to the surrounding as
  Longitudinal Waves

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Sound in Air

• Vibrations are sent to the surrounding as
  Longitudinal Waves

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Sound in Air

• Vibrations are sent to the surrounding as
  Longitudinal Waves

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Sound in Air

• Vibrations are sent to the surrounding as
  Longitudinal Waves

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Sound in Air

• Vibrations are sent to the surrounding as
  Longitudinal Waves

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Sound in Air

• Vibrations are sent to the surrounding as
  Longitudinal Waves
• Compression areas of high pressure
• Rarefaction areas of low pressure

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Media that Transmit Sound

• Sound must have a medium in order to travel
• In a vacuum, there are no molecules to transmit
  the vibrations

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Media that Transmit Sound

• Sound travels in the air at 340 m/s at 200 C
• Speed increases by .60 m/s for every 10 C
  increase
• As thermal kinetic energy increases, speed of
  sound increases

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Media that Transmit Sound

• Question
• How far away is a storm if you note a 3 s delay
  between a lightening flash sound of thunder at
  200 C?

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Media that Transmit Sound

• Answer
• 340 m/s x 3 s 1020 m

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Media that Transmit Sound

• Light can travel about 100,000 m in the same time
  it takes sound to go 1 m

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Media that Transmit Sound

• The distance light can travel in 1 s takes sound
  8 months to travel

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Media that Transmit Sound

• water
• Sound travels 1482 m/s in fresh water
• About 4x faster than air

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Media that Transmit Sound

• water
• Sound travels 1522 m/s in salt water
• About 4x faster than air

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Media that Transmit Sound

• Question
• Why does sound travel faster in salt water than
  it does in salt?

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Media that Transmit Sound

• Answer
• Because salt water is more dense.
• Salt water has more molecules closer together in
  order to transmit vibrations

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Media that Transmit Sound

• Solids
• Sound travels 5960 m/s in steel
• About 18x faster than air

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Media that Transmit Sound

• Speed of sound is increased by
• Temperature
• Density
• Elasticity

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Media that Transmit Sound

• Ultrasound
• Easily reflected off organs

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Sound level

• Question
• What is the difference in the sound wave produced
  from hitting your desk hard compared to hitting
  your desk soft?

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Sound level

• Answer
• Amplitude

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Sound level

• Intensity
• Tells how much power reaches your ear per unit of
  area
• Watts/meter2

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Sound level

• Intensity
• P IA
• P 4pIr2
• E IAt

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Sound level

• Intensity
• Directly related to the square of the amplitude
• Intensity varies inversely with the square of the
  distance.
• As distance doubles, intensity decreases to 1/4

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Sound level

• Loudness
• Our perception of sound
• Not directly related to amplitude
• Affected by pitch and tone

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Sound level

• Decibel scale
• Used to measure sound level
• ? (10dB) log I/I0

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Sound level

• Decibel scale
• Intensity is logarithmic
• 10 dB 20 dB is an increase of 10x
• 10 dB 30 dB is an increase of 100x

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Sound level

• Decibel scale
• Loudness perception
• 10 dB 20 dB is an increase of 2x
• 10 dB 30 dB is an increase of 3x

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Sound level

• Decibel scale

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Forced Vibrations

• The vibration of one object can force another
  object to vibrate
• Guitar string sets the sounding board into
  vibration
• Sounding board sets more air molecules into
  vibration
• Sounding boards make sound louder
• Important for all stringed instruments

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Natural Frequency

• Every object, when disturbed, vibrates at its own
  unique frequency

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Natural Frequency

• Depends on elasticity shape of object
• Elasticity refers to the ability of an object to
  return to its original shape after being
  distorted

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Natural Frequency

• Natural frequency is reached when minimum energy
  is required to produce a forced vibration

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Resonance

• When the forced vibration of an object matches
  the objects natural frequency

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Resonance

• Sound resonates if the objects are elastic.
• Steel is elastic and resonates
• Putty is not elastic and does not resonate
• Remember, elasticity and stretchability are
  different

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Interference

• Remember the slinky lab?
• 2 waves generated from opposite ends but on the
  same side resulted in constructive interference

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Interference

• Remember the slinky lab?
• 2 waves generated from opposite ends and on
  opposite sides resulted in destructive
  interference

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Interference

• Sound interference
• Constructive interference is louder
• Large compression waves

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Interference

• Sound interference
• Destructive interference are areas of no sound
• Large rarefaction waves
• Produce dead spots

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Interference

• Destructive interference can be useful
• Noise canceling earphones
• contain microchips that produce
• mirror image compressions and
• rarefactions
• Can cancel about 95 of noise

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Beats

• When 2 slightly different frequencies vibrate
  together
• Tremolo effect

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Beats

• Beat frequencies are calculated by subtracting
  the 2 frequencies
• 250 Hz 252 Hz have beat frequency of 2 Hz

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Music

• Open pipe resonator
• Resonates only when its length is an even of
  quarter wavelengths
• 2/4, 4/4, 6/4, etc. (1/2, 1, 1 ½ )
• Brass, flutes, oboes, sax

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Music

• Closed pipe resonator
• Resonates only when its length is an odd of
  quarter wavelengths
• ¼, ¾,
• clarinet

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Music

• Open Closed pipe resonators resonate at more
  than one place
• Singing rod

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Music

• Fundamental
• Lowest frequency making up sound

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Music

• Harmonics
• Waves of frequencies that are a whole multiple
  of the fundamental

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Music

• Octave
• 2 notes with frequencies of 21 ratio
• Ex 440 Hz
• 1 octave below is 220 Hz
• 1 octave above is 880 Hz

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Noise

• Large of frequencies with no relationship but
  with equal amplitudes
• Very soothing

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Sound Technology

• Hi fi uses all ranges that can be heard
• 20 Hz 20,000 Hz
• Telephone systems only use 300Hz 3,000Hz
• Range most spoken language is heard

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White Noise

• Large of frequencies with no relationship