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I'm an electrical guy, so I know how to make a frequency converter electrically. Or by using software through resampling, etc. My mechanical understanding of the world is much more lacking. What I'm wondering is if there is a purely mechanical way of changing the frequency of a sound? Is it possible in theory or are there working devices that do this?

I'm not talking an ideal device, some smoothing / muddling of the frequencies would be fine. Just in general, say it was human voice - to roughly move the frequency down an octave from the original person's voice - or say, take a high frequency hum of a high speed metal fan blade and take the high frequency sound it creates and create a more pleasant, low frequency hum. In my mind, I'm thinking something like a resonating chamber except it actually changes the frequencies rather than just amplify them.

My first thought (probably stupid) is some sort of small, isolated gas inside a bladder inside a resonator? Like a bladder full of helium or sulfur hexafluoride? Second thought (also probably stupid), maybe a chamber full of wooden balls and/or tubes similar to a wind chime?

Just to be clear: I'm talking a device that would create sounds at a frequency or frequencies that completely did not exist in the original sound. Not something that would simply filter out certain frequencies and resonate others.

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    I guess you could have something that resonates at one frequency, and a machine that translates that vibration into energy to drive some other underrated (in frequencies) sounds generation device. I can't imagine how to practically work out the energy mechanically though. – Linuxios Apr 20 '17 at 3:48
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By far most passive acoustic systems are linear and time invariant. As such, they don't create frequencies not present in the original signal.

Passive systems that aren't linear are typically of the snaring/clacking variety. They either create overtones to existing frequencies, or they have their own strong resonance but are triggered by external signals.

Your isolated gas inside a bladder inside a resonator is likely linear. The resonator's frequency will determine the strength of the response, but the response still will not contain frequencies not in the original signal.

Your chamber of wooden balls and wind chimes is a better bet: it's the snaring/clacking variety.

  • Thank you for the explanation. As an engineer (though not mechanical), I'm a little embarrassed that I didn't think about the LTI nature of the bladder idea. – Trashman May 1 '17 at 14:47

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