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.
What do these "even" spikes mean?
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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Hint: You have to count nodes & antinodes of a single closed end pipe.
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.