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You may have seen it being worn by content creators or attached near instruments but what is a contact microphone exactly?
A contact microphone is an electronic device that uses a transducer to convert sound vibrations into electrical signals from the surface rather than the air. It has a diaphragm mounted on aluminum, brass, or other conductive materials to make it easier for sound waves to hit and produce vibrations. Once there’s vibration, the sound waves are converted into an electrical signal that will be amplified and sent to a recording device of your choice.
It’s also easy to see how contact microphones are often confused with boundary microphones or lavalier mics because of their design, use, and attachment. However, the main difference is that contact microphones are designed to be in physical contact with the sound source instead of other types of microphones that capture sound from the air. Additionally, a contact microphone can also be called a piezo mic or transducer mic.
As contact microphones need actual contact with the object or sound source when recording sounds, this equipment is great at recording non-electric instruments and small objects. Acoustic instruments, woodwind instruments, strings, and drums are most suitable for contact microphones. As for objects, items like glass, paper, and thin strips of metal can be recorded by contact mics.
Do take note though that contact microphones are not that sensitive to high frequencies so we would not recommend using them to record cymbals or hi-hats.
The most common and basic type of contact mic is a dynamic one. This has a transducer, a coil, and a magnet to convert sound vibrations into electrical signals. There’s also a condenser contact microphone that essentially has the same design but is just more sensitive when picking up sound. There are also ribbon contact microphones and pre-assembled contact mics with an XLR phantom-powered preamp.
Since contact mics pick up vibrations from the surface rather than from the air, one would need to properly attach them to the object or sound source that will be recorded. Below are the two easiest and simplest ways to attach a contact microphone to an object or surface.
There are plenty of affordable adhesives in the market that can be used to help attach contact mics.
The first method is by using the trusty double-sided sticky tape. Since it’s thin and extra sticky, you can be assured that the contact microphone will be attached securely to the surface without causing any blockage on the vibrations. However, double-sided sticky tape can be quite difficult to apply because of how thin and fiddly it is. It can also leave some residue on the contact microphone device so make sure to get everything out and clean it properly afterwards.
The second method is using sticky tack. What makes this a good method is that it’s easier than applying double-sided sticky tape and it’s reusable to a certain point. However, do make sure that you don’t use too much sticky tack to make it too thick as this can prevent the contact microphone from picking up any vibrations from the surface and result in poor audio recording quality.
Beeswax is used for various foundations such as candles, metal castings, food processing, and more. However, it can also be used as a good long-lasting adhesive. However, there are a few more extra steps you will need to do to keep beeswax sticky.
You will first need to gather a cup of beeswax pellets, 2 teaspoons of olive oil, and 1 ½ teaspoons of lanolin. In a bowl, gently heat the oil and lanolin together. Afterward, add in the beeswax pellets until completely warmed up. Add in an extra teaspoon of oil to slightly firm up the wax before you stick it to either the surface or the contact microphone.
As the beeswax is thinner and can evenly spread out, the sound recording captured by the contact microphone is somewhat clearer than the other attachment methods. You can hear that the frequencies and sound are evenly spread and vibrations can be picked up.
When attaching a contact mic to an acoustic guitar, one will need a few more items than adhesives. Since an acoustic guitar being played will most likely be moving, you will want to use a cable longer than 8” to clear the jack, sticky tack to attach the contact mic to the surface of the guitar, and gaffer tape for added security. The gaffer tape helps keep the contact mic more secure from possibly falling off the guitar, especially when there are vibrations.
While you can experiment with where to put the contact mic on the guitar, we recommend placing it just below the guitar’s bridge or on the side of the high strings. This placement will keep the contact mic in good proximity to the guitar sounds and prevent any signal interruptions.
A good contact mic has a sound design that can pick up minuscule vibrations and specific signal levels. However, since contact mics have high electrical impedance, using a buffer preamplifier from the recording device will make a recording sound better and louder.
A contact mic powered with a preamplifier can help fix issues on high impedance or low frequencies disappearing from a sound recording. A preamplifier will also give you a better bass response. If you’re not sure you’ll need this, then you can monitor your mics via headphones or through a computer.