on ebay, i keep losing out on bids on Realistic PZM mics...

ufoclub said:

I got 4 of em they very cheap in the shops

Make Your Own PZM Microphone
by Terry Williams

For those of you not familiar with these mics, they are designed to decrease the amount of echo or reverberation when recording in a large room. They accomplish this by putting the microphone pick-up element, or capsule, very close to a flat surface. This flat surface is called the boundary. That is why this type of microphone is also called a boundary microphone. By getting the microphone capsule close to the boundary it cuts down on the dizzying array of reflected sound waves hitting it from all angles. The waves that are reflected off of the closely positioned boundary are much stronger than waves that have bounced all around the room. This makes the microphone become more sensitive, and helps keep the audio from sounding like you recorded it inside of a big steel drum.

Both PZM and PCC microphones are flat and are designed to be mounted to a wall or placed on the floor or a table top. The bigger the boundary underneath the microphone, the better it will perform. The PZM, or “pressure zone microphone”, is an omni-directional microphone. The PCC, or “phase-coherent cardioid”, is directional in nature, picking up sounds from in front of the mic, while rejecting sound from the sides and behind the mic. Both are manufactured and trademarked by Crown. Radio Shack makes a version that is much less expensive, but doesn't work nearly as well. Crown also makes a less expensive version called the “Soundgrabber II”. It works better than the Radio Shack version, but still nowhere near as well as the real PZM or PCC. However, these mics cost hundreds of dollars, and most videographers already have a regular hand-held microphone. If only you could use the microphone you already have. Would you believe with a few well placed pieces of foam, you CAN turn your handheld mic into a boundary mic?

This can be accomplished by laying your microphone on the floor or against a wall with a small piece of foam or rubber material underneath it. Enough to separate it from the surface by a quarter to half an inch while insulating it from vibrations. You want the mic capsule to be as close as possible to the floor (or wall) without touching it and you don't want any of the material to be directly between the capsule and the boundary. To be most effective the boundary should be a hard, reflective surface that is at least one square yard in size. That is why floors and walls work best. Of course, if you use a wall you will need some duct tape or gaffers tape. I know that this process sounds very strange, but doing this will make your handheld work just like a true boundary mic. The directionality of the setup will depend on the pick-up pattern of your microphone. If you have an omnidirectional mic it will act like a PZM. Likewise a cardioid or hyper-cardioid mic will act like a PCC.

There are a few more things to keep in mind. The better the microphone the better this will work, and the more sensitive it is the better. In fact it is best to use a condenser or electret mic because they are generally more powerful. But whichever you use, turning it in to a boundary mic can increase its sensitivity by 3 to 6 decibels. It will also not sound nearly as reverberant as the typical handheld mic on a stand or mounted on the camera. Just as with any mic placement you should strive to get as close to the subject as possible and avoid anything that might cause interference or block the sound.

Try this technique and I think you'll agree it is worth the effort. It will also work when using mics for sound reinforcement. It's nice to have a bag full of mics, but when you can't afford it take along a bag full of items to make your mic act like other types of microphones.