The PZM has a hemispherical pickup pattern when used on a boundary like a floor, wall, ceiling or tabletop. Another way to look at that is to say that it is omnidirectional above the boundary plane. This makes sense when you consider that it generally can't pick up sound from behind the boundary. The PCC microphone is a directional (half-supercardioid) boundary microphone that rejects sound from the side and rear. This directional pattern adds gain-before-feedback.