The Physics of Sound: What is Sound?

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Sound is a vibration that we can hear.

Sources of musical sounds include:

  • vibrating strings (guitar, violin)
  • vibrating columns of air (clarinet, pipe organ)
  • vibrating diaphragms (drums, timpani)
  • virtual electronic vibrations played through a loudspeaker (electric piano, synthesizer)

Since an acoustic piano makes sound by vibrating strings, let’s use a vibrating string in our discussion on acoustics. If you pluck a string, it will vibrate back & forth like this:


As the string moves, it compresses the air around it, changing the air pressure from high to low to high to low every time the string goes back & forth & back & forth. This pressure change travels at the speed of sound in all directions until it reaches your ears, causing your ear drums to vibrate at the very same frequency. This vibration of your ear drums is relayed to your brain via a bundle of nerve cells where it is perceived as the pitch of the vibrating string.



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