The Medium: Contact Microphones

The immediate question that followed the decision to acoustically study my car was... how? I was not interested in the sounds that I normally hear, therefore a typical microphone was not the most suitable answer.

I decided to use contact microphones that I built using piezoelectric discs. Following the directions of "Handmade Electronic Music: The Art of Hardware Hacking" by Nicolas Collins, I began experimenting with different kinds of Piezo Discs that I extracted from toys, buzzers, smoke alarms, etc. Piezo Discs are widely used as buzzers in most toys that make basic sounds, they are mass produced and are very cheap. Rather than a buzzer, they also work much better as a contact microphone when they are properly wired and connected to an amplifier.

Piezo discs use piezoelectric properties of crystals to create high pitched noises when a voltage is applied. They are made by bonding a thin layer of ceramic or crystal to a very thin, flexible brass disc. The first series of piezo mics that I made came from Piezo Buzzers bough from The Source and an old smoke alarm. These discs worked when I connected them to the shielded audio wire and then to a small 9volt amplifier, but the quality of sound was weak and there was a lot of static noise. This was due to every part of the construction being the bottom of the line. I soon realized, that with electronics... you get what you pay for.

This is a series of recordings that I did with the 9volt amp and the piezo disc from a buzzer. The disc was set up on 5 different places.
1. The engine
2. The wind sheild
3. The wheel well
4. The muffler
5. The radio speaker

The trip was the same for each recording, however the rhythm was changed by traffic, stop lights, speed, etc. Each track is played simultaneously. This is a 30 second clip from the original video.