Optional Practical: Boomwhackers

Introduction

A boomwhacker is a musical instrument in the form of 6 plastic tubes that if hit against your hand emit a note. The frequency of the note is related to the length of the tube, since they are open at both ends the wavelength of the fundamental will be 2 x length.

Method

The frequency of the sound can be measured by recording the sound on your computer then using the program Audacity to analyze the frequency spectrum and measure the frequency of the 1st harmonic. To try this out:

  • Make sure your computer microphone is switched on then open the programme Audacity. If you don’t have the program it can be downloaded from  http://audacity.sourceforge.net/
  • Press the Record button and hit the boomwhacker on your hand near the microphone.
  • You should see the recorded sound in the audio track window.  You can drag this to make it bigger and zoom in on the portion you are interested in.
  • Select “plot spectrum” from the analyze menu to display the frequency spectrum
  • Place your cursor over the biggest peak to find the frequency of the 1st harmonic.

Analysis

By measuring the frequency of the note produced by all of the boomwhackers use a graphical method to find the velocity of sound in air.

Note: You can get boomwhackers from toy shops but I bought mine from Ebay.

Boomwackers 

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