underworld

In Part 1 of this Design Idea (DI), we saw how a standard electret microphone capsule can be persuaded to detect infrasonic signals down to a fraction of a Hertz by adding some fairly simple equalization. In this second and concluding part, we will improve that circuitry and also add an audio output to allow…

Editor’s Note: Part 1 of this DI uses an electret mic to create infrasound. It starts with a basic equalization circuit validated with a DIY test fixture and simulations, and ends with a deeper analysis of the circuit’s real response. Part 2 includes refinements to make the circuit more usable while extending its detectable spectrum…