know a boundary microphone, also known as pressure or PZM microphone Zone, a brand stands for Crown International, a small opening to allow the sound waves of a small diaphragm microphone immediately adjacent to get a hard surface. The sound waves a few millimeters away from a form of hard surface area or pressure boundary layer, interaction between molecules and surface acoustic waves to carry the waves in phase.

In a Boundary Microphone, also know as a Pressure Zone Microphone or PZM, an acronym trademarked by Crown International, a tiny opening allows sound waves to reach a small mic diaphragm immediately adjacent to a hard surface. Sound waves a few millimeters away from a hard surface form a pressure zone, or boundary layer, in which interaction between the sound wave molecules and the surface bring the waves into phase.