A couple of months ago, Collin's Lab featured a story about making your own piezoelectric crystals from Rochelle salt. Collin stopped short of making an actual microphone though: he just demonstrated that the salt crystal would generate a series of voltage spikes when whacked with the handle of a screwdriver. Leafcutter John followed pretty much the same recipe to make crystals of his own, and then clamped the crystal between the jaws of a little panvise, and hooked it to an audio amplifier. When a small music box was held near the crystal, a surprisingly high fidelity recording resulted. Check it out!