or supercardioid. One method to create a directional boundary mic is to mount panels (hard surfaces) next to an omnidirectional mic capsule. Another method to create a directional boundary mic is to use a small-diameter (1 cm or less) directional mic capsule mounted on a boundary surface, with the axis of the microphone parallel with the surface. As shown on manufacturers' datasheets, the mic capsule retains its directionality (cardioid or supercardioid polar pattern) and prevents comb filtering by keeping phase interference above the audible range. Examples include: Crown Audio PCC-160 introduced in January 1985. Shure SM-91, which is also commonly used inside a kick drum for sound reinforcement. Audio-Technica U843R, which has three cardioid condenser elements in the same housing plate, which allows for multiple, user-selected pickup patterns (levers allow the reorientation of the capsules; as well, individual capsules can be turned on or off). The predecessor of the directional boundary microphone was a directional microphone placed in an Electrovoice Mic Mouse, a foam block that suspended a conventional microphone horizontally just above a surface. Because conventional microphone diaphragms are relatively large (> 1 cm diameter), phase interference from surface sound reflections caused a rolloff in the high frequencies of a microphone in a Mic Mouse. Some applications for directional boundary mics are picking up actors' voices onstage in drama or musicals; picking up the footwork of dance troupes; picking up speech at conference tables, boardrooms, and the pulpit in a church; and recording small musical ensembles or soloists. Boundary mics intended for boardroom use may have a range of additional features that are helpful in a conference setting, such as an "on" indicator LED, an on-off switch (or a "push to talk" or "mute" button), and wireless capability to allow easy repositioning during the event. References External links PZM Condenser Mic - clear concise description Pressure Zone Microphones - History and other information Two different boundary microphone types 22 Years of the Crown Mic Memo (includes early PZM history) Basics of the boundary microphone / PZM Microphones