Christian Liljedahl

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Noise free, balanced piezo microphone

Getting true balanced output from a piezo element

At illutron, we are using piezo elements a lot 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. 


Using two piezo elements sandwiched, back to back, you can generate a balanced signal, that will be completely noise free.


This is how to do it

  • Use two piezo elements
  • Sandwich them "belly-to-belly" (crystal and wires in, metal out)
  • Join the two (black) wires from the capsules and connect to Gnd on your xlr / microphone-cable
  • Connect the centre wire (red) from piezo A to + (hot) and the red from piezo B to - (cold) on your xlr / microphone-cable


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. 


Further studies

                • Mapping the frequency response of the hydrophones
                • Making directional hydrophones
                • The effect of putting a small piezo against a bigger one



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