Balanced Piezo Contact Microphones

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 is a recording we did with two balanced piezos mounted on pieces of burning firewood.

Headphones are recommeneded - Enjoy! :-)

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.

Comments

[sam.bronstein]

This is great! Can you share the sample sounds some other way? Link isn’t working :)

[chrlilje]

Ah, thanks - Looks like my friend have deleted it from Soundcloud. I will ask him tomorrow if he can dig it out from somewhere :-)

[nortok00]

Hello. I came across this project while searching for diy contact mics and really want to try this. I'm new so forgive the newbie question.

The only part I don't understand is wiring the cables (XLR and microphone). Are we choosing to wire just one of the cables (so choose the XLR cable or choose the microphone cable depending on the needs) or are we wiring the piezo and both of the cables together? I understand your wiring schematic for one cable but not wiring both. Reading the instructions hasn't clarified and none of your pictures show the cables in detail. Can you clarify?

[chrlilje]

Hi nortok00 - I am not sure I fully understand your doubts, but i'll try to clarify.
I use XLR cable and microphone cable in a confusing way I think.
A microphone cable usually have an male XLR plug in the end.
In the other end of the microphone cable, we attach our two piezo disks.

The XLR plug goes into a mixer, typically, or directly into an active speaker sometimes.

You will use 2 piezo disks for 1 microphone cable with 1 male XLR plug in the end.

I have attached an image of the finished piezo, hopefully this will also clarify.

Do let me know if you have further questions, and I will try to answer as good at I can.

[nortok00]

Thank you! Now I understand (or hope I do). So it's just one cable I'm buying and not two? That would make sense. In your list of things needed I thought it was a microphone cable and an XLR cable and that had me confused as to how these would be wired to the piezo.

[chrlilje]

You just need 1 cable. The microphone cable has 3 conductors inside. A shield (ground wire), a red and a white wire. Those are the ones I refer to in the drawing :-)

[nortok00]

Excellent! Thanks. This makes perfect sense now and I'm excited to attempt this project!

[ChristianL4]

Hi nortok00 - I am not sure I fully understand your doubts, but i'll try to clarify.
I use XLR cable and microphone cable in a confusing way I think.
A microphone cable usually have an male XLR plug in the end.
In the other end of the microphone cable, we attach our two piezo disks.

The XLR plug goes into a mixer, typically, or directly into an active speaker sometimes.

You will use 2 piezo disks for 1 microphone cable with 1 male XLR plug in the end.

I have attached an image of the finished piezo, hopefully this will also clarify.

Do let me know if you have further questions, and I will try to answer as good at I can.

[DickT7]

What is the black washer looking piece on the outside?

[chrlilje]

A little late reply, but the black plastic disk around the piezos are just the way our piezos came from the factory. They have no electrical purpose, but I could imagine they make the piezo a bit more sturdy.

[bergamotewilks]

I did the soldering, then didn't have silicone so stuck the piezos together with blue tack and it works, finaly a buzz free sound, thanks a million!
I was wondering, it is important to make sure that the metal discs don't touch each other, isn't it?

[chrlilje]

We have done different configurations - Sometimes back to back or side by side with the two piezos. As MikB points out - The most important thing is, that the white disks does not touch each other in the middle.

Our reasoning for putting the metal disks outside and to ground was, that this would effectively extend the cable shield all the way out and around the piezos, giving the best possible protection against noise.

[MikB]

Yes it is: As shown above, the gold/brass discs are electrically connected to each other as "ground". But when physically mounted, the "white" discs are apparently next to each other. If these touch they will short out the signal.

[ApoC2]

Hey there,
Awesome project and really stunning results!
I'm trying to use the piezo on my guitar (classic guitar {non-electric}) and welp, I'm getting hell loads of noise, I've seen that when people did it on their guitars, they pre-amped, could that be the reason? Should I make a pre-amp circuit? (I don't know if it would help increasing the picked-up melodies as well)
I'd really appreciate any possible help, and thanks a lot in advance!
(and anything else should I keep in mind as a piezo newbie? :D)

[chrlilje]

First make sure you can get the piezo working noise-free outside of the guitar.
And make sure you connect the piezo to an input that is actually a balanced input. (xlr-input)

Usually the noise comes from some part of the piezo electrically connecting to something, picking up 50Hz noise.

What kind of noise do you get? Is it 50/60Hz line noise or other?

Hope you get it working :-)

[MikB]

Nice bit of lateral thinking: The output from a piezo is very high impedance and so very easy to interfere with. The normal way to solve this is to put a preamp right there with the piezo, to give some "robustness" to the signal. This solves the problem in a different way.

It's like a humbucker pickup technique, but not using magnetics!

[bergamotewilks]

This is more than lateral thinking, it's lateraly balanced thinking! :)

[-deef-]

Hi there! I just came across this instructable and think this is exactly what I'm looking for. I'm amplifying the sound of a very large and heavy rock wobbling on a stone tile. The sound this produces without any amplification is already quite loud.

At the moment I'm trying to figure out what kind of preamp I'll need. Can someone tell me how to choose the right preamp for the kind of sound I'm amplifying?

Thanks in advance!

Regards,

Dave

[Aud1073cH]

What did you use for the housing (the black ring seal around the edge)?

[mofuzz]

One great tip I learned from <a href="http://www.nicolascollins.com/handmade.htm">Nic Collins</a> is to dunk the piezo and lead wires in some Plasti-Dip. Two coats is what he recommends. It makes the whole apparatus water proof, protects those delicate wires that are soldered to the piezo, and has surprisingly little effect on the response of the microphone.