What is a boundary microphone?

Boundary microphone or pressure zone microphone (PZM), is a generic term for microphones taking advantage of the special acoustic phenomenons occuring directly at the surface of a plane boundary i.e. a floor, wall or table top. Normally they are omnidirectional microphones specially designed for this purpose with the diaphragm placed flush with the surface of a plate or a disc working as a pressure zone. Also, normal omnidirectional microphones will work fine as PZMs if for example, taped to a wall or floor.

Although most boundary microphones follow the format of a condenser element mounted to a plate and covered with a protective screen, there is one important variation. Recessed boundary microphones aren’t attached to the plate and don’t have a protective screen. These mics are designed for fixed-install mounting in a wall, ceiling, tabletop or podium. They are designed to be visually discrete yet provide the same performance or traditional boundary microphones.

So what?

Because of the combination of increased direct sound pressure, and reduced diffuse sound, boundary microphones are popular in an number of applications. The boardroom conference table is the most common use. This environment has a several reflective surfaces and often more than one person is speaking at once. The use of a boundary mic removes the need to mic each person individually, or to deaden the room with acoustic treatment.

Another common application is on podiums or alters. In these instances, the main advantage is the ability to clearly pick up a voice without having to be in close proximity to it. This frees the speaker to move around and to gesture without moving out of range, or hitting the microphone.
The boundary microphone is therefore a useful addition to any audio installers armoury.

This article was prepared with help from the DPA Microphone University

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