Here is some
wisdom information I’ve collected on the subject of contact microphones. Anything which appears on this page, I have made a solid attempt to vet as worthy of consideration. I’m no expert, merely a sound designer who has done some exploration. I started this page simply to collect my own research, then thought I might as well share.
A contact mic will usually consist of two parts: a transducer (typically a piezo disc or film), and an electronic device performing some combination of impedance matching and amplification. The output of this device will connect to a mic pre, recorder, or mixer.
The transducer will then be physically coupled to a sound source using adhesive, clamps, magnets, beeswax, weights, sticky-tack, physically fit into a narrow or tight space, or anything else that couples vibration into the transducer.
Please note: it matters what preamp you plug these into. There are various matters of impedance and mic preamp slew rates and power handling that can have a significant effect on sound. You’ll want to consider your whole system, not just what’s listed here. I use a 702T, 788, grace lunatec v2, and original sound devices mixpre, and get nice results, whereas I’ve had mixed results with a Sony PCM-M10 pocket recorder, and with a Mackie mixer. Transients can be extreme with contact mics, and preamps with less headroom can distort. When impedance is not properly matched, odd things can happen like electronic noise from the recorder bleeding into the audio, or loss of low frequencies. So… check out your whole system.
As with most things, details matter… and I urge you to consider the work that others have put into making operational the simple practice of plugging a piezo disc into a recorder or mixer.
In my experience, it’s often surprising what you discover with contact mics. Interesting sounds can become boring, boring sounds can become interesting, and the location of your transducer and how it is attached can matter a great deal. Whatever you do, I hope you enjoy exploring.
Paired Transducer+Electronics Plug and Play Systems
Do check things out w/ your intended mic preamp first. Lots of high-quality gain will help. See above note.
- Trance Inducer has a very good reputation, and I’ve heard some stunning recordings done with it. Primarily Trance Audio makes instrument pickups; the “Inducer” is a sound-design oriented product which includes two of their “acoustic lens” transducers, paired with a stereo amplifier. Please note – it’s quite expensive and is a special order item with a long lead time.
- Aquarian H2a hydrophone and phantom-powered XLR variant, while optimized for use in liquid medium, can be used as a contact mic. Being somewhat heavy cylinders, they can take some experimentation to mount successfully to some sound sources, however they sound quite good and clean. Cheryl Leonard uses them to great effect, coupled to wood, bone, stone, and other materials.
- Barcus Berry is favored by many musicians, and can be used as a contact mic. Their model 4000 is for piano, so can handle wide dynamic range and frequency range.
- An oldie but goodie, if you come across one, is the FRAP. If Neil Young and Michael Hedges base their guitar sound on it, you know it’s can’t be bad. However sometimes music products aren’t properly matched for professional recorders; Ann Kroeber had a specially made FRAP used for a great many fascinating recordings, but I believe it was a one-off.
- Zeppelin Cortado MkII a coated piezo disc, wiring, and coupled phantom-powered amplifier packaged in a small tin box.
Piezo Transducers – Wired for Use (but likely need impedance matching and/or amplification)
- Jez Riley French makes very nicely wired and assembled piezo discs for contact mic use. Care is put into the physical construction and materials, to help them perform well in creative sound capture scenarios.
- contactmicrophones.com AKA Cold Gold Audio sells pre-made units and parts at reasonable prices.
- Barcus Berry 4000 transducer is available independently from the electronics.
DIY – Raw Transducers, Build Instructions and Ideas
- For raw discs, Murata 35mm diameter piezo elements were mentioned in forums as good. But this is an area I have very little info. Specific products can be searched for at electronics suppliers such as Mouser and Digikey. I’ve seen mentioned: [Murata 7BB-35-3]
- Also note: wire length matters, shorter is better. Shielding around the pickup and wiring matters, and quality of cable matters both electronically and in terms of cable-borne mechanical noise.
- Zach Poff “Building Contact Mics” is an excellent resource for physical build and all manner of valuable thinking.
- The amplifier on Zach’s page has been described as “noisy” so I’m not recommending it.
- PDF of Schematics generously assembled and shared by Richard Lerman at Arizona State University. Using this you could build your own amplifier. I’m unsure of its sound quality.
Impedance Matching Amps + Adapters for use with Piezo Transducers
These are essential to good sound. Without it, your piezo disc will form a high-pass filter in conjuntion with your preamp, and the resulting sound will be very thin. These can be used with a raw transducer you wire up yourself.
- TritonAudio BigAmpPiëzo 7.5Mohm – a convenient 1/4″ to XLR package, containing a phantom-powered FET amp and impedance matching circuitry.
- Jez Riley French sells an impedance matching adapter. This is a passive device, not an amplifier, so for quiet sounds will pair best with a quality preamp with plenty of gain; the idea is also that louder sounds will come through well. Find on his order page.
- Stompville sells a Phantom Powered Piezo Preamp Module which is intended to be built into an instrument. It’s less costly than TritonAudio, and reported to have a great sound. They are small enough to consider placing the amp very very close to the transducer, which is ideal for sound. I’ve seen photos of a slightly modified one placed inside a small metal lip-gloss canister along with a transducer.
Aaron Brown has posted a shootout recording of a contact-mic’d clothes dryer over on soundcloud, featuring all six possible combinations of Barcus Berry transducer and Cold Gold transducers with adapters from Barcus Berry, Triton, and a Hosa impedance matching adapter. The Barcus Berry transducer sounds nice, the BB and Triton adapters sound nice.
Thanks to Garth Paine, Nathan Moody, Jez Riley French, and members of Field Recording facebook group (particularly this thread) for contributing info and feedback.
LOM has published fantastic contact mic resource page with a lot of explanation and quality links. I recommend you check it out.