After doing a little research on various websites and conferring with some knowledgeable Twitter acquaintances, I decided to try building a contact mic. What finally put me over the edge were the recordings at Tim Prebble’s fantastic website, The Music of Sound. Since these devices measure vibrations picked up through objects rather than air, the recordings take on an amazingly exaggerated character. This process renders audio fodder that is perfect for further processing into larger-than-life sounds.
The fact that a contact mic can be built for only a few dollars means that the barrier to entry is almost zero. Let’s take a look at the process of building one of these devices, and at the end I’ll link you to some monster growling sounds I made while testing the mic.
First, let’s take a look at the required materials:
- soldering iron and solder
- piezo transducer (Radio Shack part #273-073A
- 1/8″ audio jack
Optional stuff that I bought:
- clamp for securing the mic to surfaces
- heatshrink tubing for covering the wires
- foam paintbrushes for covering the piezo, itself
The first step was to break the plastic casing off from around the piezo element. Needless to say, patience is a virtue here because you have to snap off the housing a little bit at a time.
Since there’s a little hole on top of the casing, I chose to wedge in a scissor blade in order to cut out a little notch. Once I cut this little flap of the plastic, I used needle nose pliers to start pulling away the rest of he housing, bit by bit.
Once I chipped off enough of the plastic, the housing basically fell apart in my hand and it became much easier to pop out the wafer-thin piezo element. As you can see, there isn’t much to this device, so you’ll want to be gentle with it. However, they’re so cheap and quick to make that it won’t be a huge issue if it does get broken.
The next step was to slip some thin heatshrink tubing over the wires coming from the piezo. I only did this as a simple way to keep the wires together and somewhat protected from the elements. (After I was done making and testing the mic, I used a hair dryer to shrink the tubing down, creating a snug shield for the wires.) Additionally, I unscrewed the sleeve off of the audio jack and slid it over the tubing so that it would be ready to pull over the jack once the soldering was complete.
Next comes the soldering. First, I tinned the two piezo wires so that minimal heat would be needed to solder them to the jack: When working with electronics this small, you can cause a lot of damage by applying extreme heat for more than a few seconds. Next, I connected the black wire to the large contact which protrudes from the bottom of the jack and the red wire to one of the contacts further up on the jack. If you’re not sure what I’m talking about, just take a look at the picture and you’ll see the correct configuration.
After soldering, I pulled the sleeve up over the connection and screwed it back on to the jack, itself. All done!
Since I was going to be using a clamp to hold the piezo firmly on various surfaces, I wanted some kind of padding to protect the delicate unit. While searching around in a hardware store I came upon some foam paintbrushes. These ended up being the perfect padding after I pulled out the handles, leaving just a piece of foam with a little slot in the middle. Just slide the piezo into the slot and clamp it onto a surface and you’re ready to record.
Now that the microphone was done, I connected an 1/8″ cable between the mic and the input on my Edirol R-09HR, making sure that the mic input mode on the R-09 was set to “mono.” I also did a few test runs in order to set the correct high-pass filter frequency and input level. I walked around the house, clamping the mic to various surfaces and listening to how they sounded when hit with various objects. The results were quite satisfying! Although I’m going to save most of these sounds for future posts, I thought I’d share three “monster growl” variations that resulted from clamping the mic to a piece of acoustic treatment in my studio while I rubbed my fingernail across the fabric.
This project was cheap and easy, and I can’t imagine being without one of these devices as a sound designer. What excites me most is that this little mic will open up even more options for creating original sounds while relying less on commercial libraries and stock effects. More posts will come in the future as I continue to experiment with different builds and surfaces to record on.Building a Contact Microphone by Nick Maxwell