Microphone Overview: Boundary Type
A boundary microphone is essentially a small diaphragm condenser mic mounted in a housing that directs the diaphragm parallel to the surface onto which it’s mounted. You can see a diagram of a boundary mic’s setup in the following illustration. The parallel setup allows the mic to pick up the sound that is reflected off the surface that it’s mounted to, such as a wall or table.
The advantage of a boundary mic is that it can pick up sounds accurately in reverberant rooms and can capture sounds from multiple sources. For example, if you were recording people talking in different parts of a room, one boundary mic could record everyone; you wouldn’t need to use multiple mics.
Boundary mics are often mounted on the floor of a stage, a table in a conference room, or a lectern of a church or large hall. Because it’s hard to find a surface large enough to vibrate to the lowest frequencies, it’s more common to use these mics for vocals, pianos, and other instruments that don’t have a super low pitch.
If you do record something like a kick drum with a boundary mic, you’ll likely need to dial in some EQ on the lower frequencies.
Boundary mics can be found in many of the same polarity patterns as condenser mics: omnidirectional and cardioid. These mics are fairly inexpensive and start under $100, though you can spend several hundred or more if you want.
The Boundary microphone employs a condenser microphone diaphragm mounted parallel to the mounting surface to capture the reflections of the sounds off the surface the mic is mounted. As the sound hits the surface that the mic is mounted to, it picks up the vibration, and the diaphragm creates an electrical charge that is sent to the preamp. These mics require phantom power to operate.