re pressure zone microphones in article rjobdinnk s crcnis unl edu mpaul unl edu marxhausen paul writes 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 yup it s not all that difficult to do 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 khz with a bit flatter response the panasonic cartridges aren t bad but they aren t spectacular 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 mm 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 don t mount it on the side call up crown the company that has the patent on the pzm and ask them for information on construction and use of the things you may have to determine the correct spacing emperically with a noise source and a spectrum analyzer because the design of the panasonic cartridges uses a tuned cavity in front of the electret element to increase the high frequency response and you are going to be altering the resistance through the cavity entrance crown has a nice book on the subject though it s unfortunately rather short on mathematics there s a jaes article from many years back too still for your application you ll be a lot better off buying the cheap radio shack models and using phil rastoczny s modifications to get a clean balanced output phil s mods seem to get reposted here on a regular basis scott
