Building XLR Contact Mics
Lately it seems all I’ve been doing is building contact mics for use in performance projects (Spilled Measures Dancing at my Feet, Run Little Girl, NATURE FETISH), along the way I have found that the usual method of using a 1/4″ cable with a small piezo (the much lauded RadioShack part #273-073 or equivalent) is not the ideal solution.
Thanks to the guidance I received from Ian M. Colletti of Vaudeville Park and the electronics collective NewBit (Aliza Simons and Gelsey Bell), I was able to supply 1/4″ contact mics for Zierle & Carter‘s performance of “Spilled Measures Dancing at my Feet” at Vaudeville Park. They had some of their own (thank goodness, there were so many sheets of metal) which had been made with XLR cable.
While testing the difference between the XLR and 1/4″ cables I found the XLRs were much more responsive (hot) and had a lot less noise in their signal.
This was something interesting to note, but has become a necessity since I’ve had the chance to work with Dreary Somebody, building contact mics for their upcoming performance of “Run Little Girl” at Merce Cunningham Studio (the last performance in the space before it is turned over to another company).
We attempted to install the contact mics upon our first arrival at the studio, only to find an extraordinary (to a musician/sound guy) lack of 1/4″ cable, and I didn’t have enough at home to run the mics (attached to paintings by Jillian Rose) to the sound system (we would have needed over 100 feet of cable).
Upon my return home I thought back to the wonderful XLR contact mics and our current predicament, realizing the best way to get good sound out of the paintings and the only feasible way to run them would be to build them with XLRs.
Because of the size of the paintings and the fact that location of the mics within them was important compositionally (the dancers had to be able to speak into them and “play” the paintings with the sound design by Esther Neff), each painting needed at least two microphones.
What follows is a brief overview of how to make two-headed contact mics:
1. Get your tools
As you can see I kept it simple:
- soldering iron
- needle-nosed pliers
- rosin-core solder
- clamp
- electrical tape
- scissors
2. Get your parts
- piezo elements (only one pictured here)
- XLR cable
- XLR connector
- wire (i used speaker wire I had laying around)
3. Solder the connector to the cable
Make sure to do this correctly, or your mics won’t work (check out this handy tutorial).
4. Solder the cable to the wire
Wind the wires that will be the ground for the mics together and attach to the ground of the XLR cable (the cable’s shielding), then attach the positive wires to the other two XLR leads (the “hot” and “cold” – shown here as the blue and white wires).
5. Solder the wires to the piezo elements
Make sure the ground wires are connected to the black wires of each piezo (they should be soldered to the outer ring of the piezo), and the others to the red.
6. Attach the mics to something and make some art!
I used electrical tape to isolate the exposed wire since if anything went wrong I wanted to be able to fix it fast. If you use heat shrink tubing your mics will look a lot more professional and be a bit more durable, but you’ll have to cut it off to get at any troublesome connection.
There you have it, an easy way to get a decent sound out of any surface. From the photos you’ll notice I didn’t shield the piezos from the elements (usually done with Plasti dip or a similar product). I wanted them to be as sensitive as possible to pick up the gentle scrape of nails or the rubbing of fingers.
Thanks to phase space’s tutorial on this, which lays this method out in more exact electrical terms, along with the trusty furious contact microphone assembly how-to. For the ultimate in contact mics, check out Zach Poff’s re-post of Alex Rice’s in-cable preamp design, brilliant!
– Brian
Nociception Theatrician 