Updated: Apr 26, 2021
“What is that thing?”
It’s probably the most common question heard around Hybar HQ. We definitely enjoy doing conventional things in unconventional ways…Want to strum a guitar? We have a funny-shaped pick for that! Want to know what a garbage dumpster whacked with a tire iron sounds like through an amplifier? We have a contact microphone for that! OK, so maybe pounding on dumpsters for their sonic nuances isn’t conventional. But amplifying sound is, and just about everything makes sound. And a contact microphone unlocks the sonic possibilities for many of the world’s “unheard” sounds.
Before we dive into the particulars of what makes a contact microphone a contact microphone, let’s take a moment to think about what exactly sound is. In simplest terms, sound is a series of vibrations that transfer energy from a source (e.g. a drum head being struck) that can be picked up by the human ear. Air particles vibrate from this transfer of energy, bumping into one another, until they contact our eardrums, which allows the sound to be perceived by a person. This is, of course, better explained elsewhere. (This video from Branch Education does the trick.)
The microphones that most of us are familiar with operate on the same principle as an ear: a person talks or sings into the microphone, which contains some kind of diaphragm. The diaphragm vibrates when the displaced air particles hit it, and the acoustic sound coming from the vocal cords is transformed into electric current. (Here’s a minute-long video illustrating that process.) The current is amplified via a power source (i.e. an amp), and the sound waves are then sent to and out of speakers (which are also diaphragms!). This creates larger vibrations that vibrate a larger number of air particles over a greater amount of space.
So what is a contact microphone? At a basic level, a contact microphone operates like any other microphone: It contains a small diaphragm that picks up sound waves and sends them to an electronically amplified device which makes the sound louder (in this case, the diaphragm is a piezo element, which works by sensing pressure. The hardcore science of how piezo elements work in general is in this Wiki article.)
The contact mic's piezo-element design allows it to capture sounds directly from the surface of an object. Unlike common vocal or instrument mics that are placed at a distance from what they are ultimately picking up, a contact mic is made to pick up vibrations by physically touching an object. You know, making contact. And this practical difference opens up a world of creative possibilities.
How to Build It
The physical build of a contact mic is pretty simple. The piezo element is soldered to the internal wires of a length of microphone cable. At the other end of the cable is either a female or male terminal, depending on the particular design.
If it’s a female end (as is the case with Hybar’s design), insert a standard instrument cable into the mic and plug the other end of the instrument cable into your amplifier of choice. If it has a male end, simply plug it into your amp. There are some good tutorials (both in text and video) if you want to try your own build:
Informative and straightforward instructions:
Another good overview of contact mics including a discussion of pre-amps:
Very in-depth with some technical discussion:
DIY til we die:
V i b r a t i o n s E v e r y w h e r e
Q: Why would you want a contact mic?
A: Because they are loads of fun.
Q: Well, what can it do that a traditional mic cannot?
A: Many things! Like Prometheus wresting fire from the gods, the contact mic takes music and sound design from the realm of instruments and brings it to the level of worldly vibration. If it vibrates, then a contact mic can make music with it. Traditional instruments are welcome, but not necessary.
Nearly anything that vibrates or makes a sound when tapped, whacked, rapped, strummed, flicked, scratched, scraped, or otherwise interacted with can become an electrified instrument with the application of a contact mic.
For example, hold the head of the contact mic against an object, let's say a cardboard box. Plug the contact mic into an amplifier. Voila! That's it. Anything you do to the box is now coming through your speaker. It’s that simple!
Attach a strip of sandpaper to one side of the box and scratch it with your fingernails; drop a bag of marbles inside the box and shake it – completely new sounds, completely new instrument. And that’s just a cardboard box. As of this writing, we have used contact mics to effect, record, and amplify the sounds of milk jugs, filing cabinets, office desks, trash cans, garbage disposals, springs, sticks, bones, stones, coffee tables, beer kegs, a reciprocating saw, glass bottles, an abandoned diesel tank, pianos, kalimbas, banjos, mandolins, dulcimers, acoustic guitars, tom drums, a djembe, bells, singing bowls, and even the human body.
Like most things in this life, contact mics are even more fun when you start adding effects pedals. While your mileage will vary using hot distortions and fuzzes (like any other microphone, contact mics do feedback), delays, reverbs, loopers, and modulation of all kinds can help create layers of sound and worlds of texture you never dreamed a cardboard box or piece of paper could produce.
If pristine sound from an instrument is what you are after, an all-purpose contact mic is no substitute for a well-selected traditional microphone or a pickup designed for that instrument. However, contact mics are a great tool for approaching traditional instruments in creative ways. For example, you could capture extra layers of an electric guitar performance by attaching a contact mic to the back of the speaker in addition to the standard mic placement up front. Or, a contact mic placed on the throat can often capture vocal frequencies not picked up by standard microphones. With a contact mic, even traditional realms are fertile ground for experimentation.
Practical Tips for Good Vibes
Contact mics present one major practical issue. You can’t just put them on a mic stand and vibrate in their general direction. They generally must make - and maintain - physical contact with the source of the vibration. And, ideally, the contact mic should do so in a way that doesn’t negatively impact the object’s vibrations. The human hand is pretty good at this; in many cases you can place the contact mic on the vibrating surface and then experiment and adapt the amount of pressure you are applying. “Free-handing” the contact mic also lets you move it around, looking for signs of vibrational life, like a doctor with a stethoscope. But, that technique isn’t always satisfactory. You'll often want the freedom of having the contact mic securely in place without having to hold it there continuously. (Your hands will often be needed for creating the source vibrations, or controlling effect devices.)
So, how do you keep a contact mic in place without it vibrating off the surface? In some instances, the natural weight of an object will be sufficient. But, in many instances, you'll need to apply some of the creativity that got you to this point to find a solution. There are myriad ways folks have found to attach a contact mic to an object: gator clamps, poster putty, magnets, rubber bands, to name a few. The easiest and most universal way we have found is every stage hand’s best friend: gaffer’s tape. Gaffer’s tape has the holding strength of duct tape, but peels off more like masking or painter’s tape. No sticky residue to remove; no damage done to the contact mic or the object being mic’ed. It isn't perfect, but it usually gets the job done. (A roll of gaffer’s tape is a nice inclusion in your musician’s toolbox, anyway).
Contact microphones are liberating devices. They allow the creative mind to make music with the raw sounds of our vibrating world. Office cabinets, utility drawers, garages, and thrift store shelves begin to look like instrument shops. Two hours at the laundromat becomes a recording session. You become the sonic translator for the vibrational messages of the natural world. For real. That’s exactly what you can do with a contact microphone. If you’d like to get started, Hybar has built a durable, versatile contact mic that is hand-wired from upcycled and quality components. Or, there are a host of other contact microphones available, many with adaptations you may find useful. Or, you can build your own. If you do try out a contact microphone, get in touch! We’d love to hear what you’ve found.
The Hybar Contact Mic is available here.
Get in touch at hybarmusic.com