Boundary Microphones

This category contains boundary microphones. A boundary microphone is a small omnidirectional condenser mic capsule positioned near or flush with a boundary (surface). The arrangement provides a directional half-space pickup pattern while delivering a relatively phase-coherent output signal. One example is the PZM for Pressure Zone Microphone. The term PZM is a contraction of Pressure Zone Microphone, and was used by the manufacturer Crown to describe its particular incarnation of a 'boundary layer' microphone design, in which the mic capsule is mounted slightly above the surface plate, looking back down onto it. Other boundary layer mic designs simply mount the mic capsule flush with the boundary surface. Both designs work in the same basic way, and there is no significant difference between them, although the PZM design affords a higher degree of physical protection to the capsule. Most boundary layer (or PZM) mics have a relatively small housing or base plate, purely for practical reasons. However, to ensure that the boost in sensitivity is maintained uniformly across the entire frequency spectrum, the pressure zone must be maintained for all frequencies too, and that means that the boundary surface requires dimensions similar to the wavelength of the lowest frequency of interest, hence the advice to place boundary layer mics on the floor or on walls. An alternative approach often used is to mount the boundary layer mic on a stiff wooden or perspex panel with the largest practical dimensions, in order to produce an area of maximum pressure near the mic. Common applications are: conference rooms, altars, stage, grand piano, kick drum, ambient mics, small acoustic ensembles in the studio.