A contact microphone (or surface microphone) is a mic that captures vibrations through direct contact with the material. Unlike traditional acoustic microphones designed to pick up air vibrations, contact microphones are notably resistant to feedback.
They are widely used to capture vibrations from acoustic instruments (such as guitars, double basses, and cellos), in sound design, electronic music, and by foley artists. They are also used in communication to capture larynx and vocal cord vibrations, reproducing the sound of the voice, and more.
Easy to build yourself as a DIY project (short for "Do It Yourself"), it’s simply a piezoelectric sensor connected to a Jack or XLR plug. Cost of the operation: less than €5. Follow this guide!
If you’re not very handy, here are a few reliable options to buy:
- K&K Big Shot (€40 approx.)
- AKG - C 411 (€170 approx.)
Building a hydrophone, a microphone designed for underwater recording, is similar but requires weighting and waterproofing, as described in this guide.
This microphone is monophonic, but you can also make a stereo version. Place two piezo sensors side by side on the same side, or build two separate microphones to control the distance between them.
Preparation
Gather a few components, either recycled or purchased:
- 2 bottle caps,
- A piezo for a mono mic, 2 for a stereo mic,
- Some hot glue or silicone,
- A cable, single for mono or double for stereo,
- A Jack plug (mono) or XLR, or two for a stereo mic.
You’ll also need some tools:
- A cutter,
- A hot glue gun or caulking gun,
- A soldering iron with solder.
Step-by-Step Guide
Step 1
Cut one bottle cap to expose the piezo’s two solder points.
Step 2
Use the soldering iron’s hot tip to make a hole on the side of the cap.
Step 3
Thread the cable through both holes.
Step 4
On the piezo, solder the "ground" wire to the outer (golden) part, and the "hot" wire to the central (white) part.
Step 5
Press the piezo against the bottle cap and secure it with tape if necessary.
Step 6
Fix the piezo in place by applying hot glue or silicone inside the cap. Be thorough: apply around the cable, in the corners, and even in the cap’s thread grooves.
Step (Optional) Weighting
This step is necessary if you want to make a hydrophone. See the instructions in this dedicated guide.
Step 7
Cut the second cap to fit as a cover for your microphone. Glue it in place while filling the first cap with hot glue or silicone.
Step 8
Solder the mono Jack or XLR plug to the other end of the cable:
- Jack: connect "ground" to the body of the jack and "hot" to the tip.
- XLR: connect "ground" to pin 1 and "hot" to pin 2.
Step (Optional) Waterproofing
To use it as a hydrophone, it must be protected against moisture. See the explanation in this dedicated guide.
Usage
Place the microphone against the surface whose vibrations you want to capture. You can fix it in place using putty, a rubber band, or a gentle clamp.
Since a contact mic’s impedance may not always match your equipment, it’s sometimes advisable to add a preamp like this.
Conclusion
That’s it! This construction is simple, as you’ve seen.
