Pressure Zone Microphone  (330-1090A)   How and Why    Faxback Doc. # 14683

PZM:  HOW AND WHY

If you are not the curious or technical type, you may skip this section and
proceed to "Preparation for use" and "Applications."  However, the PZM is
so different, we think you'll want to know more.

Conventional microphones have always be hindered by interference between
sound coming directly from the source and sound reflected from the primary
boundary (the wall, floor, or ceiling closest to the microphone).  This
interference happens because the direct and reflected sounds reach the
microphone at slightly different times.  This results in reinforcement of
some frequencies, cancelling of others, and an overall unnatural
reproduction of the sound.

The PZM design eliminates this interference and actually uses a combination
of the direct and reflected sound waves to achieve its amazing sound 
reproduction.  The PZM contains an electret microphone capsule permanently
mounted a short distance from its attached primary boundary plate.

When the sound waves strike this plate, a 'pressure zone' is created in the
space between the electret element and the boundary.  In the pressure zone 
the direct and relected sound waves are coherently in phase and reinforce
each other.

The electret capsule detects the changes in pressure in the pressure zone,
rather than the moving sounds waves, and therefore is unaffected by the 
distance of the sound source from the microphone or the angle of the source
to the microphone (as long as the source is within the hemisphere pattern
above the primary boundary plate).

Note:  For best frequency response, especially bass response, the PZM
       should be mounted on a hard, flat surface at least four feet square.


(SP/all-04/20/95)