Boundary layer microphones or pressure zone microphones (PZM) bypass the sound reflection from reflective walls and floors. To minimize the influence of possible interference and standing waves, the microphone capsules of boundary layer microphones or pressure zone microphones are integrated into a large, sound-reflecting surface, preferably a boundary surface such as a wall or the floor. Such an embedded microphone picks up only the sound pressure, not the sound velocity.
Since the reflections occur at the boundary surface wall in which the microphone capsule is flush-mounted, they are not picked up by the microphone. The design results in a flat frequency response. The situation is different for microphones that are placed in front of a wall and pick up the reflecting sound waves, resulting in interference. The pressure buildup that occurs in front of the boundary microphone is twice as great as the sound pressure in the open space, so the sensitivity of the boundary microphone is doubled.
As a result, the output voltage is +6 dB higher than that of conventional microphones. Boundary microphones have a hemispherical, frequency-neutral polar pattern. They are designed as condenser micro phones or sometimes as electret micro phones.