PZM (microphone) - The Directional Boundary Microphone

The Directional Boundary Microphone

A directional boundary microphone is a boundary microphone with a directional polar pattern such as cardioid or supercardioid. One method to create a directional boundary mic is to mount panels (hard surfaces) next to an omnidirectional mic capsule. An example is the Crown PZM-2.5.

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 are the Crown PCC-160 introduced in January 1985, the Shure SM-91, and the Bartlett TM-125.

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 and boardrooms, and recording small musical ensembles or soloists.