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Just now a bumblebee flew past me (more than a meter away), and for a moment its prominent droning sound seemed to make a vibration on my face I could feel. It made me wonder: consider a bumblebee, cicada, or military submarine that produces a loud monotone sound, perhaps aimed to some degree by a beat pattern between multiple sources. Is it possible for it to then hear some "echo" returning on a different frequency, originating from objects that are set to vibrating by the sound? This seems analogous to visual fluorescence, though my intuition tells me that the echoes might be either higher or lower frequency than the original sound.

For this question I'll exclude Doppler effect, though it is technically an example. I'll also exclude overtones of the original sound broadcast, unless for some reason they are only returned by specific objects based on their nature or composition, and sonoluminescence - that is an interesting case in which sound creates a return with a trillion times more energy, but I'd like to restrict this to returning sounds.

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The acoustic response of most objects is quite linear, so you will only receive signals in frequencies that were transmitted. However, there are indeed non-linear acoustic effects, which could cause this. One example might be a buzzing caused by sound waves that cause something to click back and forth between two constraints. My car has a slot for coins, and I can get a very high frequency sound out of them due to low frequency road noise.

Its easy to see that such an effect can cause a higher frequency. Can it be lower? I think so, but the math is more complex. A few years back I asked about the practice of "warming up" a gong, which involves lightly tapping a gong several times before playing it. This practice produces a brighter tone. Apparently the non-linear mechanics of a gong are tremendous. From my reading of the answer, there is a complex interplay between high and low frequencies, suggesting that indeed one could produce a lower frequency sound.

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  • $\begingroup$ Thanks - this is a useful insight and search term. Going to Wikipedia for nonlinear acoustics yields a link about how higher harmonics are returned by tissues in different degrees in sonography. But 'nonlinear' seems more like a classification than a description - I'm hoping to see a more specific analysis. $\endgroup$
    – Mike Serfas
    Commented May 26 at 15:22
  • $\begingroup$ Perplexity.ai answered my headline with a "no", and when asked the full two paragraphs, it gave an answer 'closely paraphrased' from your text. But the second time I asked it added a sentence, which I had it explain further, about materials with non-linear stiffness (material yielding, gaps/clearances, or geometric effect) and non-linear damping (friction, fluid effects, or inherent material behavior). But the sources it cited that I could access didn't immediately appear relevant... $\endgroup$
    – Mike Serfas
    Commented May 26 at 15:46
  • $\begingroup$ Your question asked "is it possible." What sort of analysis were you expecting? $\endgroup$
    – Cort Ammon
    Commented May 27 at 1:21

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