TAPE HORIZONS: Microphone Types (Aug. 1975)

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by CRAIG STARK

MICROPHONE TYPES

AT one time, most open-reel tape recorders came with their own micro phones. Although these mikes were fine for voice, they were certainly less than suitable for high-quality recording, as their owners soon discovered. Today, only the portable cassette machines come with microphones, and those are frequently built in. From time to time, therefore, I get inquiries about choosing mikes for tape decks, and I am some times asked if I can recommend a book.

Until now, my answer has been "no," for there just weren't any to recommend.

At last, however, there is. Written by Lou Burroughs and edited by John Woram, Microphones: Design and Application (Sagamore Publishing Co., 980 Old Country Rd., Plainview, N.Y. 11803: $20), is a volume intended for professionals and serious amateurs, as its price alone indicates. And while you don't need advanced math to comprehend it, it is heavy on theory and packed with frequency-response curves and graphs.

Besides microphone facts, Burroughs also points up some misconceptions about mikes. For example, if you go to an audio dealer in search of a pair of mikes, one of the first questions you'll get is, "Do you want omnis or cardioids (unidirectional)?" The former pick up sounds from all directions, while the latter reject sounds from the rear, and so need to be "aimed" in the direction of the sound source you want to record.

The dealer's recommendation will al most invariably be the cardioid micro phone, the reason being the desirability of "eliminating" background noise and increasing separation between channels.

This is a popular misconception which can be exposed with a simple test.

Set up a cardioid mike in the room in which you normally record, and with chalk, tape, or newspapers, make a circle six feet in diameter around it. While you man the recorder's controls, have someone stand at the circle's edge in front of a microphone feeding into the left channel and repeat, "one-one-one-one-one" as rapidly as he can. (The repetition will help him keep his voice at the same level.) Now, keeping the same voice level and repeating the "one-one-one..." monosyllable, have him walk around the circle, facing the mike, while you note the time (or tape index-counter settings) he reaches various points on the 360-degree circumference. Rewind the tape, plug in the right channel, and repeat the experiment, but this time out side the house in a quiet spot.

When you compare the playback of the left (in room) and the right (outdoor) channels, you won't need any instruments (though if your VU indicators read the playback levels, they'll confirm it) to tell the difference between the two: the rejection of sounds coming from be hind a "unidirectional" mike may be quite satisfactory out of doors, but it will be very slight in your recording room.

It's no fault of the mike that sounds originating from the rear bounce off the front wall, and thus also reach the front of the cardioid in time, drastically diminishing its practical advantage over that of the omnidirectional type. But, given the inherently smoother frequency response of an omni in the same price range, your choice is no longer quite as easy as the salesman's automatic recommendation of the cardioid made it seem. When I started taping concerts years ago, I wouldn't even consider an omnidirectional mike. Now, when I can switch-select either unidirectional or omnidirectional pickup patterns with the same mikes, I find I use the latter most.

What you won't get, either here or in Burrough's book, are hard-and-fast rules for microphone placement or selection.

Time and again I've heard studio engineers debate about how they'd use only such-and-such a mike, at a distance of "X" inches for a clarinet pick-up, but for drums they'd not consider anything but a so-and-so (or a pair of them), spaced so far apart .... Maybe in their rooms and conditions those choices are optimal, but no two rooms are exactly alike.

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Also see:

CLASSICAL DISCS and TAPES

TECHNICAL TALK, JULIAN D. HIRSCH

 

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Updated: Friday, 2025-08-15 13:43 PST