As a complete oversimplification, a microphone is an instrument which measures differences in air pressure.
It is not surprising that somebody would, in light of the interest in Quadraphonic sound, experiment and perfect an instrument which would measure and transduce the differences in air pressure around a full 360 degrees - to effectively create a quadraphonic microphone.
Figure 1 (click to enlarge)
Such a truly Quadraphonic device, developed by engineer Carl Countryman and producer Brad Miller, is in external appearance no different than the several models of standard microphones (Figure 1).
This Quadraphonic microphone has been designed and built using the case and chassis of a Neumann SM-2, into which four independent microphone heads have been built to provide full 360-degree pick-up.
The pick-up patterns (Figure 2) are cardioid, front and back, and figure-8 at the sides.
Although the obviously complicated matrixing data are proprietary, and unavailable for publication, the discussion of pickup patterns, generally, yields an understanding of how the design provides excellent separation and naturality of sounds.
Cardioid, also sometimes called unidirectional, is a heart-shaped response. It is resultant of an omnidirectional and figure-8 pickup.
The signals are superimposed on each other; at the very rear they are anti-phase, and so cancel out.
At the front they are in phase, hence the tapering hear-shaped response toward the rear.
Figure 2 (click to enlarge)
Figure-8, or bi-directional pickup-patterns, are the result of two directional pickup patterns, one in phase and the other anti-phase.
The output at the front and the back are equal, although opposite,.
As the input signal moves to the side, the output is gradually reduced until at 90 degrees, the two patterns have, for all intent and purpose, canceled each other out.
Figure 3 shows microphone capsules as they are arranged in the microphone head.
“Front to Back” and “Left to Right” are one above the other at 90 degrees to each other.
Three demonstrations, on very spontaneous, served to convince that development of the unit is very nearly complete.
Figure 3 (click to enlarge)
The microphone was hung in Miller’s back yard garden, surrounded by about 200 degrees of sound source emanating from a waterfall with various small tributary streams flowing from it. It presented an excellent opportunity to “hear” the complete environment; the waterfall in stereo on the two speakers in “front,” and from behind, the beautiful ambiance of the total environment and the reflected sound.
Several minutes into the demonstration, on the Southern Pacific tracks bordering on the rear of the Miller garden, a slow-moving freight train ambled by. The completeness of the sound, the way it engulfed the listening room, is difficult to describe. It was totally complete… almost frighteningly so.
Figure 4 (click to enlarge)
Miller completed the demonstration by playing a 4-track tape of his “Mystic Moods Orchestra” on an especially adapted Sony. The machine (Figure 4) has been adapted for 4-track, in and out, and will be able to accommodate 10-inch reels of 2-inch tape.
The machine is the forerunner of a new design from the Countryman/Miller collaboration which will weigh in the vicinity of 20 pounds.
The “Mystic Moods” piece only served to further impress that Quad or Multi is certainly on the way… with an endless spectrum of sound combinations and tonal effects.
Editor’s Note: This is a series of articles from Recording Engineer/Producer (RE/P) magazine, which began publishing in 1970 under the direction of Publisher/Editor Martin Gallay. After a great run, RE/P ceased publishing in the early 1990s, yet its content is still much revered in the professional audio community. RE/P also published the first issues of Live Sound International magazine as a quarterly supplement, beginning in the late 1980s, and LSI has grown to a monthly publication that continues to thrive to this day.
Take the PSW Photo Gallery Tour of audio equipment ads appearing in RE/P magazine, circa 1970
Our sincere thanks to Mark Gander of JBL Professional for his considerable support on this archive project.