Closed tube standing wave

  • Thread starter exaramco
  • Start date
  • #1
3
0

Main Question or Discussion Point

Standing waves have a fundamental frequency equal to 4x the length of the pipe if the pipe is closed at one end and open at the other end.

So, blowing across the top of a 33.2 cm bottle should produce a fundamental frequency of v/4L or about 340/1.2= 283 hz. When I record the sound produced by this bottle and then run a spectral analysis (I have done this several times) sampling at both 1000 hz and 44khz I consistently get a fundamental frequency of 96 hz with harmonics at multiples of 96 hz. A closed end tube should produce only odd harmonics.

What is going on?
 

Answers and Replies

  • #2
130
0
A bottle is not a pipe.
A bottle often works as a Helmholtz resonator.
This is probably what happened in your experiment.
 
  • #3
3
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Right you are! I changed to a pipe and the spectrum came right on target. Thank you.
 
  • #4
3
0
In fact, when I plugged in the equation for the resonant Helmholts frequency, it came at about 100 hz--just what I measured. Thanks again.
 

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