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In other words, what is the similarity between a lightning bolt and a wobbling sheet that make them sound alike?

It seems to me that the two systems have a much different way of moving the air, and probably if you could hear it up close, a lightning bolt wouldn't make the sound of a wobbly metal sheet. I think maybe the many reflections and how they interact with the cylindrical shape of the thunder-wavefront may be what gives the similarity.

dotancohen
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Ryan Thorngren
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    I suppose I would first want to know if the two sounds are actually similar in terms of waveform analysis. I agree that they sound similar to my ear, but perhaps this is just an artifact of human perception. – Tim Goodman Aug 15 '12 at 21:46
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    That is a good point. I'm not sure how to reason about that aspect of the problem besides assuming it's a small effect and that the spectrum is indeed similar (at least in a certain range of frequencies, 20-20000Hz as is our hearing range). – Ryan Thorngren Aug 15 '12 at 22:18

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Here is a thought:

With some experimentation, I've found that a sheet, when wobbled gently, makes a 'wub' sound which has a different spectrum than rolling thunder. However, when wobbled violently, the sheet forms bulges which narrow and sharpen and then suddenly flatten, making a loud 'blap' like a thunderclap. The reverberations in the sheet of this flattening seem to give the rolling effect of thunder.

Indeed, the sudden flattening looks like it creates a the sort of sharply single-peaked pressure wave I expect close to a lightning bolt. I asked a friend who lives where there is plenty of lightning, and he confirmed that close to lightning, there is no rolling thunder.

This suggests to me that there is a similarity between how the flattening reverberates in the sheet and how the thunderclap reverberates across a landscape.

EDIT: I don't think the sound comes from the whipping effect at the bottom of the sheet because a similar sound happens with an aluminum foil sheet, where the sound is definitely not coming from the whipping of the bottom, which doesn't get very fast with aluminum foil.

Ryan Thorngren
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