Infrasonic Upshifter

It is possible to buy such a thing as a bat detector.

This device has a microphone to pick up ultrasonic sound (actually, all sound), and a circuit that heterodynes it against a (selectable) high frequency, before outputting it to a speaker. The net result is that ultrasonic sound gets shifted into the audio range, and hence becomes hearable.

The results are really quite surprising, even in the absence of bats. You would not believe how much high-frequency noise there is in the world. The jangling coins in your pocket become cacophanous; a mechanical wristwatch sounds like a maniacal gong; a crisp fiver, when crumpled, becomes an artillery barrage. All in all, £39.99 well spent.

Howevertheless, what about infrasonics? We are assured that elephants communicate through the ground using low-frequency sound, and that the Earth itself rings like a huge bell at every minor earthquake. But can we hear this? No, we cannot.

Proposed, thenceherewith, is the Infrasonic Upshifter. Its front end is a simple microphone, but with a relatively large mass attached to the diaphragm. Placed on the ground/floor/table, it will respond well to vibrations down to a few tenths of a Hertz.

These low-frequency vibrations are up-shifted by some slightly clever circuitry, into the audio range. Naturally, there will be some lag (a 1Hz vibration will take at least a few seconds to be registered, analyzed, and reproduced as audio), but that's OK - elephants say very few things that require an urgent response.

What, you may ask, is the point? What if you have no elephants nearby? Well, who knows? The world is rich in ultrasonics that we usually don't hear, so who knows what variety of infrasonics are out there waiting to be heard? That earthquake in Eastern Pangal? The pile-driver thirty miles away? The hitherto- unknown infrasonic chit-chat of cows? The possibilities are unlimitless!