Yesterday, during a trip to the loft to rummage through my boxes of cables I came across a pair of Realistic PZM Microphones which I hadn't thought about in twenty years. If there was one pieces of equipment which represented a sea change in my expectations about recording, these arguably were the biggest change of all.
Prior to using these PZMs I regularly recorded band practices and jams, invariably using the built-in microphones in various portable cassette recorders. The sound was appalling, in my defence this was in a period which predates any pretensions I had of being any kind of "recording engineer", I was just a kid playing music with my friends. As a record of what we played these working tapes were flawed in that the preset microphone gain on a typical portable cassette machine was fixed and clipped terribly when faced with the kind of frenetic Space-Rock my friends and I were recording at the time. Our solution at the time was to move the recorder out of the room and down the corridor, resulting in rather distant sounding recordings (durr!).
My then girlfriend's dad had a cassette deck with 1/4" jack mic inputs and variable input gain and when paired with these PZMs it enabled a revolution in recording quality for me. Getting control over the input gain could have been achieved with any suitable microphone but these PZMs stayed around until the mid 90s as, and this is hard to imagine these days, before the introduction of the early Rode mics, the choice for a budget mic with a good high frequency response and decent sensitivity was an AKG C1000 or a Realistic PZM (and the AKG wasn't exactly 'budget' to me at the time).
The PZM is an interesting design and one I still rate. The Realistic PZM was a copy of the Crown design. I like PZMs so much that I bought a Crown PZM for a teaching studio a few years ago. By their nature boundary mics are very suitable for use in small spaces and a single PZM can capture a very natural drum sound.
PZM Vs Boundary
The PZM is very similar to the boundary mics with which they share their appearance. While PZM mics are boundary mics, not all boundary mics are PZMs. Invented in the late 70s and produced by Crown, and in their low cost incarnation by Tandy/Radio Shack, the PZM mounts an electret capsule just above a flat plate and, placed in this "pressure zone", the mic benefits from a "free" 6dB rise in level due to its placement at the boundary. The size of the boundary on which the mic is mounted affects the frequency response and given that I often used to use these mics "free standing" with just the 5"x5" steel plate it's not surprising that they were bright. In fact these mics had a positively stratospheric frequency response. This goes some way to explaining why they were so popular 20-30 years ago but have fallen out of favour more recently.
Bright Mics For Tape
The brightness of the PZM partnered very well with the less that perfect top end response of modest tape machines. The huge influx of cheap condenser mics was yet to happen and given the poor noise performance of cassette multitrackers the poor noise performance of the Realistic PZM in standard guise wasn't as important as it would be today. There are several well known mods which can be performed on Realistic PZMs to convert them to phantom power and balanced operation but the availability of cheap, high quality condensers mean that today the Realistic's days would be over even if they hadn't been discontinued years ago. The Crown PZM is an excellent mic but isn't cheap and as no-one else makes a PZM there really isn't much activity in this area. There are some high quality boundary mics available, the most well known being the SM91 but I for one would like to see PZM's make a return.