A piezoelectric disc can be used to either generate sound by running electric current through it can, or when contacting a surface, translate the vibrations of that surface into sound.
Piezoelectricity describes the naturally occurring electric charge found in certain geologic materials. This property was first discovered in crystals in 1880 by Pierre Currie, who along with his wife, Marie Currie, famously went on to discover radioactivity. He observed that when physical pressure is applied to certain crystals they emit electricity. Thus he named this property after piezein, the Ancient Greek work for “squeeze.”
– from Sonic Geologic – the Secret Life of Material Objects
Here’s a little step by step piezo tutorial.
Zach Poff has a terrific page that includes plenty of information and great construction ideas:
BUILDING CONTACTS MICS
Even MORE resources:
- the post on Nicholas Collins work that includes a soldering demo
- the post on making Piezo pickups by John Grzinich