I remember, back before commercial mikes with the "PZM" label (for
Pressure Zone Microphone) started showing up, I read an article,
in some engineering journal, that described the principles involved.
All the physics aside, from a practicle standpoint the author's said
they built a prototype with nothing more than a small Sony lavelier
mike laid up against a large aluminum disk.  In demonstrating it at
a presentation to audio engineers, this was impressive enough that
the people present were bugging them about where they could buy them.

Anyway...I want to build some to use as "choir mikes" (wide coverage).
I've had good luck using some small electret mike elements I got
from Digi-Key - most of these are limited-bandwidth, peakey units
but for a buck or two more I got the ones spec'd to go out to 20kHz
with a bit flatter response.  

The distance of the mike opening from the flat plate is kind of
critical.  I'm debating whether to mount it on it's side, which
puts the opening a shade under 2mm from the plate, or mounting
it with the opening actually pointing down into the plate at a
small clearance.  I haven't dissected a unit like you can buy at
Radio Shack to see how they do it.  Thoughts?

