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what is resonance?

  • instruments vibrate at their natural frequencies when somehow disturbed by plucking, striking, strumming, etc.
  • the natural frequencies of an instrument can be referred to as its harmonics

in brass instruments

  • an instrument can be forced to vibrate at one of its harmonics if a second object (which is connected to the instrument) pushes the instrument with one of the instrument's natural frequencies
  • this is resonance
  • brass instruments like trumpets, tubas etc. typically have a mouthpiece connected to a long tube
  • this tube serves as a container for air
  • the vibration of the player's lips when they blow air into the mouthpiece matches a range of frequencies
  • one of these frequencies matches the natural frequency of the air inside the tube
  • the air creates resonance vibrations
  • these vibrations create loud sounds

in woodwind instruments

  • try cutting a 'V' in the top of a straw as shown
  • place the cut end of the straw against your lip gently and blow until you produce a sound
  • the vibrations against the cut end of the straw produce resonance vibrations, again
  • if you cut the straw at the opposite end (so you have the same instrument, just shorter), the wavelength and frequency of the vibrations decreases and increases, respectively, producing a higher pitch

am radio

  • the antenna of a radio receives thousands of sound waves, but the tuner separates these signals by resonating at a particular frequency
  • this is how a radio picks up only one station at a time

human ear canal

  • we can find the natural frequency of the ear canal by:

f=v/4L (the speed of sound is ~343m/s and the avg ear canal is ~2.3cm)

f= (343) / (4*0.023)

f= 3728

  • the tympanic membrane has a damping effect, however....

human ear canal

continued

  • because of this damping effect, the range of frequencies we can hear is typically much wider and between 2000 and 4000 Hz
  • sounds in this range require less intensity to be heard at the same loudness of sounds outside this range

RESONANCE

karen lau

L2D blue

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