Closed tube standing wave

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Discussion Overview

The discussion revolves around the phenomenon of standing waves in closed tubes, particularly focusing on the fundamental frequency produced by a bottle compared to a pipe. Participants explore the implications of different resonating structures and their effects on frequency measurements.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant asserts that a closed tube should produce a fundamental frequency of 283 Hz based on the length of the pipe and the speed of sound.
  • Another participant challenges this by stating that a bottle is not equivalent to a pipe and suggests it may function as a Helmholtz resonator instead.
  • A later reply confirms that switching to a pipe yielded expected frequency results, aligning with the theoretical predictions.
  • Further, a participant calculates the resonant frequency of the Helmholtz resonator and finds it consistent with their measurements, suggesting a correlation between theory and experimental results.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the initial frequency measurement from the bottle, but there is agreement on the distinction between a bottle and a pipe, as well as the applicability of Helmholtz resonance in this context.

Contextual Notes

The discussion highlights the differences in resonant behavior between bottles and pipes, indicating that assumptions about the nature of the instrument can significantly affect frequency outcomes. The implications of using different resonating structures are not fully resolved.

Who May Find This Useful

Readers interested in acoustics, wave phenomena, and the physics of sound production may find this discussion relevant.

exaramco
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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?
 
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A bottle is not a pipe.
A bottle often works as a Helmholtz resonator.
This is probably what happened in your experiment.
 
Right you are! I changed to a pipe and the spectrum came right on target. Thank you.
 
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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