Although harsh noise musicians swear by contact mics, they are useful for many recording purposes. Made out of a Piezo Transducer or Piezo Speaker Element, they are small and thin enough to fit just about anywhere and measure vibrations. This first article I am going to tell you how to build them. Next article I will show you some uses for them. After that, I will teach you how to turn ordinary speakers into microphones to pick up a wider range of tones.

But first, on to the building…

From what I am told, Piezo Transducers labeled 700hz to 10khz create an ideal mic. But any large frequency range should work fine. Without getting too technical, transducers with a large frequency range generally produce a better sound because they pick up a broader bandwidth of sound. The larger the range, the more “depth” (for lack of a better term) of sound you will get. Whatever you choose, make sure that it is just the transducer or element. Stay away from anything with electronics inside. It will cost you more and you’ll just scrap the motor and circuitry in the end anyway.

Two types of piezo transducers

You may find your transducer either bag or inside a plastic case. If it is in a plastic case, you will need to crack it open carefully and get the brass transducer out. I am guessing that you will probably run across these the most. You can pick them up and just about any radio shack. You can also use Piezo Buzzers, but due to their limited frequency range, they do not work as well as the transducers or speaker elements.

I use a small jeweler’s screwdriver, but for certain cases, you may need to squeeze the outside gently with a pair of pliers just enough to crack the case, but not enough to bend the transducer. Remember, not only are they made out of a very thin brass, transducers have a ceramic coating in the center that if you chip, will make your contact mic less effective (or so I’ve been told.)

I told you they were the same

Once out of the case, you can see that the two transducers are pretty much the same. Besides the size, the only big difference is that the tiny one has an optional “feedback” line (the blue wire.) If you find that your transducer has one of these, you can either ignore it completely, or attach it to ground. The ground is generally the long metal piece on either a ¼ jack or a ¼ plug. In this case, you would more than likely be attaching it to a ¼ jack. But they basically look the same.

Example of a ground on a ¼” jack

Just because it is bigger, I will use the large transducer for demonstration purposes. I got this from a kid that went to Finland who randomly purchased transducers for contact mics but doesn’t know how to solder . . . so he gave it to me. You can find transducers such as these sold as “Midi drum trigger element” (or something to that effect.)

The first thing you will need to do is pick up a ¼” cable at radio shack. It doesn’t matter what is on the other end as long as one end is ¼”. Go with a cheap one and it will be easier if you pick unshielded because there will be less coating to strip off the wires. My favorite ones are kind of flat and you can see the two separate wires coated in plastic running parallel to each other (see the picture if this description sounds convoluted.) You can definitely use an XLR, but most of them are not only shielded, but more expensive.

See the two separate wires

Cut one end off, but make sure if the cable you chose isn’t ¼” – ¼” jack that you keep the ¼” end intact. If it is one of those cables like in the picture, you will have to pull your two wires apart and strip the plastic coating off. Luckily, they are cheap so it is pretty easy to pull them apart and then take a pair of wire strippers to them.

Attach contact mic to cable

Next, wrap your wired from the transducer around the bare wires of your mic cable. Solder these connections just to ensure they stay. Remember, when it comes to cables, if two wires aren’t touching, there is probably a good reason for it. Wrap each wire individually with duct tape or electrical tape to ensure that the metal from one wire does not touch the metal from the other.

Protection from possible shorts and interference

You are basically done now. You can put some heat-shrink tubing over the wires you just taped to ensure that the tape holds, or you can wrap more tape around it. My next article I will show you ways you can use your contact mic and how it can be a handy tool in any musician’s studio.