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  1. Why do we only have odd numbered harmonics at one-end closed tubes, however, if we do a frequency spectrum we have some periodic spikes between the odd harmonic spikes, just like the picture below shows.

  2. What do these "even" spikes mean?

enter image description here

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closed as unclear what you're asking by Ben Crowell, Kyle Kanos, Buzz, FGSUZ, Jon Custer Jan 29 at 15:06

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    $\begingroup$ Question 1 is basic freshman physics, and is discussed in textbooks. Question 2 is much more difficult, and there is no way for us to answer it without knowing all the details of what was done here. You're trying to explain peaks that are down by about 20-30 dB in sound pressure (?=French "nivel?"), which would be 40-60 dB in energy. At that level, we need to know if it's flanged or unflanged, uniform or nonuniform bore, shape of cross-scection, how you excited it, and where you measured the response. How certain are you that this is not harmonic distortion in the mic? $\endgroup$ – Ben Crowell Jan 24 at 16:09
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  1. Hint: You have to count nodes & antinodes of a single closed end pipe.

  2. The suppressed even harmonics presumably indicates that the actual "single closed end pipe" can behave partly like a second open end, i.e. an antinode.

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    $\begingroup$ Another hint: draw a picture of a closed tube, and show all of the harmonics that "fit" the tube. The rules are: 1) a node MUST be at the closed end; 2) an antinode MUST be at the open end. After drawing 3-4 different harmonics for a given tube, you'll see a pattern. $\endgroup$ – David White Oct 27 '18 at 2:13

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