This project first appeared in MAKE Volume 38, on page 85.
A contact microphone is a small device that can be used to amplify acoustic instruments. Unlike the more common types of microphone, you do not sing or talk into a contact mic. As the name implies, it does its trick by making contact with a solid object and turning mechanical vibrations into electricity. Because a contact mic does not pick up all the ambient sounds in the room, it allows you to focus in on one instrument without interference or feedback.
If you wanted to amplify your acoustic guitar, for example, you could attach a contact mic to the body of the guitar. Commercial versions use a small suction cup. For this project, we will use gaffer tape. In fact, you may already have everything you need lying around the house. I am, of course assuming that you fancy yourself a bit of a musician and already own a low-powered practice amp. Maybe you have built the Cracker Box Amp from MAKE Volume 09?
The main ingredient in this project is the mic element itself, a piezo disc. Piezos are used as lo-fi bleepy speakers in smoke detectors, old cellphones and computers, and handheld video games, and they emit a high-pitched whine when you give them some current. They also work the opposite way — in a beautiful bit of symmetry: apply current, get vibration; apply vibration, get current. That means the same device can be used as either a speaker or a microphone, depending on which way you wire it up. (This is actually an old trick. Need to record a bit of dialog, but don’t have a microphone? Plug in an extra pair of headphones into the mic input!)
Share yours: #piezomic