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.
Home made piezo crystals + homemade amp and dehummer used to make noise.
Audio file: http://skruntskrunt.ca/a/skruntskrunt-left-4.5k-piezo-ceramic-right-homegrown-crystal-toothbrush.ogg
Source code: https://github.com/abramhindle/visualize-audio-with-images