PCCs and PZMs are both boundary mics.
"
PZM" is addressing the Pressure Zone
Microphone concept and while
Crown has a trademark on both "Pressure Zone
Microphone" and "
PZM", the patent on the concept expired in 1999, so there are other mics using the same concept, however they can't use the trademarked terminology. The actual concept involved is a mic
element facing and parallel to a large 'boundary' surface. By getting the
element close enough to the boundary surface, in the pressure zone, any reflections off the surface have a relative
phase to the direct sound that results in summation up to higher frequencies, the small distance between the
element and reflecting surface pushes the frequency where
combfiltering occurs up high enough to not be a factor. This means more
gain from the summation and less problems with
combfiltering than traditional microphones on a stand.
The
PCC uses a
cardioid element mounted perpendicular to the boundary surface. By keeping the
element very small and located very close to the boundary surface, the resulting interference from reflections also occurs at very high frequencies. This same general concept is often applied when measuring loudspeakers or
speaker systems, the measurement mic is place very near a large reflecting boundary surface in order to minimize the
effect of '
ground bounce' and push the resulting interaction up to frequencies above those being measured.
I've used the
Crown SASS with success many times as a stereo ambient or archival recording mic by mounting it to a balcony
face or ceiling 'cloud' in theatres and concert halls.