measure the speed of sound

The speed of sound has been measured in so many ways but this version I saw my colleague Ian Galloway* demonstrate perfectly, impressed so I want to pass it on.

  1. Split the cable on some unwanted ear-bud earphones so that the left and right ear pieces are a metre apart.
  2. Separate and tape down the ear pieces on the bench and put the plug into the mic socket of your computer.
  3. Now start the (free) program ‘Audacity’ and get it to record sound from the ear pieces. Find the setting that gets the program sampling fast as possible.
  4. Now make a sharp sound near one ear piece and stop recording.
  5. Zoom massively into the graph and measure the time between two peaks that correspond to the sound recorded at each earbud. Calculate the speed of sound based on this time and the distance the sound had travelled.


*That’s Ian G shortly after he did the speed of sound experiment

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