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Pressure Shock!

A PZM Mic for under £20. Sound value?

Curtis Schwartz sounds out a PZM microphone that sells for less than £20.

I had been eager to have a look at these microphones for some time (PZM microphones for under £20 — I couldn't believe it). They are small flattish objects with a long lead extending from their rear with a jack on the end. Surely such a simple looking object could not produce an even half decent tone?

Conventional microphones can have problems when it comes to miking up instruments in a reverberant environment. This is one factor that goes to make microphone placement so critical. For a microphone will not only pick up the sound waves coming direct from a sound source, but it will also pick up any reflections of the sound, which can change the tone dramatically, emphasising those frequencies that it might be in phase with, and cancelling out those with which it may be out of phase.

The principle used with PZMs actually uses the reflected sound waves to achieve its sound quality. The sound waves strike the plate, and a "pressure zone" is created in the space between the electret element and the plate. In this pressure zone, the direct and reflected waves are coherently in phase and reinforce each other.

The electret capsule picks up the changes in pressure in the pressure zone, rather than the moving sound waves, and therefore is unaffected by the distance of the sound source from the microphone (as long as the sound source is within the hemispherical pick-up pattern above the plate).

For optimum bass response, the base plate must be placed on a flat surface at least four foot square, built from a similar material to the baseplate itself — glass, wood, or metal etc. I used these mics for many different sound sources, from vocals to timbales, and I usually placed them on a large window which looks out from the drum booth. I found that double-sided tape was the best thing to use to adhere the mics on to such surfaces.

Since any sound that is in the microphone's hemispherical sound field will sound 'on mic', the sound is very clear and the natural ambience of the room itself in which you are recording will have a bit more sparkle and presence to it. This is one of the many factors that go to make PZMs so popular for recording grand piano, as the acoustics of the piano structure itself play a large part in the overall sound quality of the piano.

Diagram breakdown of the PZM microphone.

Without any equalisation, these mics have a very bright direct tone, but not harsh. I used a pair of them as ambient mics over a closely miked drum kit, and the result was excellent for cymbals, hi hat etc and also added a bit more crispness to the overall tone of the drums, especially the snare.

There is a small amount of hiss present in the microphone's output, but as their tone is naturally bright, no top end needed to be added which might otherwise have increased the hiss to an unacceptable level.

The output of the microphone is preamplified with its own power supply, one single AA size battery, before continuing to the jack plug. The manufacturer suggests using two alternative batteries to the AA, which have a much higher voltage, but cost almost a third of the price of the mic itself. This would, however, improve the maximum sound pressure level to 135dB, as well as improve the dynamic range.

For a microphone to perform as well as these PZMs, and which costs only £19.95, there is very little criticism that can be aimed at them. If you want phantom powering, or Cannon connections, it would be easy enough to modify these mics to your own specifications. But as they come, they are an excellent choice for the home recording enthusiast, and without phantom powering etc, they are appropriate for portable recording — of plays, or even conferences.

Getting a good sound from these mics is almost as simple as plugging them in — the only important factor being the distance from the sound source to the microphone, which determines the amount of room ambience.

It goes without saying that this microphone qualifies for a ten out of ten for value for money, and with careful 'beefing up' of the bass, then this mic is capable of competing with microphones with three figure price tags.

These mics are available from Turnkey or your local Tandy store.

Also featuring gear in this article

Previous Article in this issue

Everything's Gone Green

Next article in this issue

Doctoring The Dr.

Electronic Soundmaker & Computer Music - Copyright: Cover Publications Ltd, Northern & Shell Ltd.


Electronic Soundmaker - Oct 1984

Donated & scanned by: Mike Gorman

Review by Curtis Schwartz

Previous article in this issue:

> Everything's Gone Green

Next article in this issue:

> Doctoring The Dr.

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