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

You need

2 normal piezo elements
Microphone cable
XLR plug

Connecting

Sandwich the two piezos "belly-to-belly" (crystal and wires in, metal out)
- We just use a wad of normal silicone sealant in-between the piezos (Think Oreos)
Join black wire from Piezo A to red wire from Piezo B and connect to Gnd on your xlr / microphone-cable
Connect the red wire from piezo A to + (hot) and the black from piezo B to - (cold) on your xlr / microphone-cable
Connect a XLR-plug to the other end of your cable

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 vimeo video have sound recordings using the balanced contact microphones: https://vimeo.com/472428276

Headphones are recommeneded - Enjoy! :-)

More about the singing strings here : christian.liljedahl.dk/strings-singing-in-a-stream/

Experience so far

The sound from the piezos are very clear and noise free
The oscilloscope have verified, that the output truely is balanced
The piezo microphone is very sensitive and responsive.

As hydrophones

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.