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Here's a short overview of how to make your own contact microphone using piezo crystals.
This technique was taught to me by Alan Lamb when we worked together as part of the 2006 Unsound Festival. He'd developed this approach for recording 'the wires,' a large-scale aeolian harp modeled on telegraph poles he recorded in Western Australia.
I'm using a couple of piezo sensors (RS part number 285-784), an RCA lead, a soldering iron, scissors or wire strippers, some tape and half a dozen cable ties.
Start by cutting the RCA lead in half and stripping the wires.
Then get ready to solder the two connections on either side of the piezo onto the wires of one of the RCA leads.
The tricky part is soldering and it's worth double-checking you've got the connection firmly soldered before proceeding.
Once the piezo are attached, you need to insulate the wires again.
I use electrical tape and carefully wrap it around one wire and then around both.
Once insulated, I attach the wires and piezos to matchsticks with cable ties.
You can use glue for this but I couldn't find anything suitable today. Alan used a sealant to weather-proof the piezo after gluing them to 'the wires' and this can extend their life considerably.
These piezo contact microphones are great for a wide variety of applications.
Today I tried using them to record a biscuit tin being used as a hand drum. I've used blu-tack to apply them but you can also sticky tape them onto a surface for temporary application, or longer depending on the tape used.
One common problem is a humming sound, which can be eased or removed by earthing the object being recorded. The biscuit tin was earthed when I held it but the Zoom H4 recorder also needed earthing by sitting it on my lap.
You can hear a short demonstration of the biscuit tin hand drum recorded in stereo with two piezo contact microphones below.
Biscuit tin drumming by bassling