I updated the swarmed post.
I’ve been playing a little bit with piezo crystals. Some good how to videos include:
You just need soda ash (baking soda that you cooked) and cream of tartar to make these crystals.
So I made some:
I hooked them up with alligator clips:
I had to amplify the crystals to hear them:
The amplifier I used is described here: Fet Amp. It is very easy to source the parts from digikey.
I made a more permanent mic out of a crystal that I soldered:
I had TERRIBLE mains hum and I tried dealing with it in analog with a Twin T Notch Filter using a 1uF and a 2.2uF and 680 ohm resistors to cut out 60hz. It did not work well:
I eventually made some csound code to dehum for me.
Here is a demo of the big crystal with the tinfoil on the right channel and a 4.5k piezo contact mic on the left channel. There’s a toothbrush involved as well.