At the illutron art ship, we are using a lot of piezo elements to make contact microphones and hydrophones (underwater microphones)
Piezo elements can be a noise nightmare. And if you are using the piezos for hydrophones, to capture underwater sound, the noise can be even more challenging, unless you get everything very well sealed.
We came up with a trick, to get a balanced signal from piezos:
Simply using two piezo elements sandwiched, back to back, you can generate a balanced signal, that will be completely noise free.
Step 1: How to make it
Step 2: Try your noise free contact microphones
Plug the xlr-connector into the balanced input of a mixer or recorder, and enjoy the crisp clear noise free sound from your piezos.
This is a recording we did with two balanced piezos mounted on pieces of burning firewood.
Headphones are recommeneded - Enjoy! :-)
Experience so far
I tried this piezo-design out as hydrophones. I could just stick them in the water and get sound. I didn't even care to waterproof them, and they worked perfectly and noiselessly under water too.
So, for quick and dirty underwater microphones, just sandwich two piezos like this and dump them in the pond.