Altec (Western Electric) 639A and 639B
cardioid directional microphones

Hear the sound of this mic set to its “R” position.

Hear the sound of this mic set to its “D” position.

Hear the sound of this mic set to its “C” position.

639A and 639B Cardioid Directional Microphones
The 639-type Microphone is a general purpose magnetic micro­phone with directional characteristics which are selectable by means of a switch. The three basic patterns available are non-directional, figure eight, and cardioid.

Sensitivity
The open circuit output level is 84 dB below 1 volt/dyne/cm², 64 dB below 1 volt/10 dynes/cm².

Power Output Level
–56 dBm for a sound pressure level (SPL) of 10 dynes per square centimeter, or –76 dBm for 1 dyne per square centimeter when the micro­phone is terminated with a resistance equal to its internal impedance. Experience indicates that the sound pressure produced at conversational level three feet from a micro­phone approaches 10 dynes per square centimeter.

Frequency Range
Substantially uniform from 40 to 10,000 cycles per second. See Figure 2.

Signal-to-Noise Ratio
The signal for 10 dynes per square centimeter sound pressure is 78 dB above the thermal agitation noise generated within the micro­phone, and 58 dB above for 1 dyne per square centimeter.

Directivity
639A
Three patterns, C, D, and R, selectable through a three-position screwdriver-operated switch. Refer to Figure 1. At the angle of minimum response, the average discrimination with respect to 0° response is 20 dB over the range from 40 to 10,000 cycles per second.

639B
Six patterns: R, D, C, 1, 2, and 3, selectable through a six-position screwdriver-operated switch. Refer to Figure 1. At the angle of minimum response, the average discrimination with respect to 0° response is 20 dB over the range from 40 to 10,000 cycles per second.

Impedance
Average value is 40 ohms. Intended for use with equipment having a rated source impedance of 25 to 50 ohms.

Dimensions
7½" high, 4⁷⁄₁₆" long, 3⁷⁄₁₆" wide.

Weight
3¼ pounds.

Description and Operation
The 639-type Microphone combines a dynamic moving coil pressure element and a ribbon velocity actuated element enclosed in a housing which serves as a protective guard and as a wind screen. The outputs of these two elements are used independently, or are combined in various proportions by means of a selector switch attached to the micro­phone, to yield several directional patterns. The 639A and the 639B are similar with the exception that the former has three selectable directional patterns, and the latter has six selectable directional patterns.

The moving coil pressure element when used alone has non-directional characteristics. The ribbon element when used alone has a figure eight pattern. The combination of the two elements results in a phasing of the output voltage causing the micro­phone to have a cardioid directional pattern. The three additional positions on the 639B micro­phone are variations of the cardioid pattern, with increasing pickup from the rear as the switch is turned from position 1 to position 3. These patterns are shown in Figure 1.

Photo courtesy of Ellis Dawson

The 639-type Microphone is an excellent general purpose micro­phone for studio use in broadcasting and recording, and for remote broadcast pickups where it can be given reasonable care in handling. In addition, the several directional patterns will enhance operation of the micro­phone where audience or background noise must be controlled, and in public address pickups where acoustical feedback would ordinarily take place before a satisfactory reinforcement level could be reached. (Figure 1 shows the angle, in respect to 0°, of minimum pickup, and is useful for orienting the micro­phone to discriminate against unwanted acoustical feedback and reverberation.) It is particularly suitable for multi-micro­phone pickups of a large orchestra group where a sense of realism and an apparent increase of volume level is desired. This is accomplished by utilizing one 639-type micro­phone as a non-directional (position D) micro­phone for general orchestra pickup and several 639-type micro­phones (positions R, C, 1, 2 or 3) as accent micro­phones for soloists and individual groups of the orchestra which the operator may want accentuated.

The general microphone will provide the necessary reverberation which is desirable for realism, and the accent micro­phones will permit the individual groups to be accented for special musical effects. Skillful operation of the mixing of the various micro­phones will permit the operator to control, over a considerable range, the liveness of the pickup.

Designed by the Bell Telephone Laboratories and originally manufactured by the Western Electric Company, the Altec 639A and 639B Multi-Pattern Cardioid micro­phones have, for years, enjoyed an unprecedented acceptance by all phases of the audio industry. Indeed, it may be stated that the majority of all wide-range sound recording—from its initial appearance on motion picture soundtracks to the present achievement of magnetic tape—has employed one or more Altec 639 micro­phones in virtually all phases of production. The immediate selection of pickup patterns provides the professional engineer with as many as six varying directional characteristics; the built-in two-stage windscreen, rugged protective housing, and numerous attachment and mounting accessories make the Altec 639 ideal for any application.

Unlike competitive units, which employ only a single ribbon and which vary the directional pattern by mechano-acoustic means, the Altec 639 is actually two independent transducer elements within a single housing. The electrical signals from these elements (one, a dynamic moving-coil; the other, a velocity-sensitive ribbon) are used singly or in combination to produce the different pickup patterns at the top of the page. Because no mechanical means are used, the Altec 639 provides increased durability, performance quality, and trouble-free operation—yet the 639’s versatility of application meets or exceeds that of all other multi-pattern units currently available.

Figure 1

Both the 639A and 639B provide the broadcast, recording, and public address engineer with performance of professional standards; the difference between the two models is found only in the amount of readily-selected pickup patterns. The 639A provides the three most widely used characteristics of cardioid, bi-directional, and omni-directional pickup; the 639B furnishes three additional directional characteristics, each having full frontal sensitivity, but with varying degrees of rear sensitivity. These additional front-to-back ratios make the Altec 639B on outstanding choice for applications wherein two distinct sound sources, having equal intensities, must be handled with utmost clarity and separation (e.g., on stage versus audience pickup; dominant speech versus a more quiet manner of speaking, on each side of the microphone).

Each directional pattern of the 639A and 639B Microphones may be easily selected with a screwdriver or similar tool, in accordance with the indicator markings on the rear of the micro­phone housing.

Figure 2

Low output impedance (30/50 ohms) permits the use of 639 micro­phones at a great distance from the associated amplifying equipment without danger of increased noise, hum pickup, or deterioration in the quality of the transmitted signal. Each 639 micro­phone is supplied with a zippered plastic bag which covers and protects the micro­phone when not in use.

Text and illustrations above are from Western Electric 639A and 639B
Cardioid Directional micro­phones Instruction Bulletin No. 1168, Issue 1.
Additional material was thoughtfully provided by Daniel L. Strong

From the Altec Lansing Corporation, Hollywood, March 21, 1950

Photo courtesy of Robert Ramirez

Frankie Laine, New York, N.Y., between 1946 and 1948

Dick Ravenhill during the 1960s at WDBO in Florida

From the Western Historic Radio Museum: The 639A was introduced in 1938 and provided broad­casters with a micro­phone that could be set to various direc­tional patterns while main­tain­ing high quality per­for­mance. Using a velocity ribbon micro­phone in combina­tion with a dynamic pressure micro­phone, the 639A offered three select­able patterns. “R” pro­vided a “figure eight” pattern by utilizing just the velocity micro­phone. “D” selected just the pressure micro­phone for a non-direc­tional pattern. “C” provided a cardioid pattern by com­bining the two micro­phones in series. The selector switch is located on the back of the 639A housing. Frequency response in any setting was 40 Hz to 10 KHz. An internal trans­former provided amplifica­tion and impedance matching for the velocity ribbon section. Western Electric also built a “B” version with six selectable pattern settings. In 1949, Altec began pro­ducing the 639 series with the ALTEC name on its models. The 639A/B was nick­named the “Birdcage” micro­phone. This particular WE639A (seen below) was used at the San Francisco short­wave station KGEI (General Electric Inter­national), famous as a broad­cast relay station to the Pacific during World War II.

Download this magnificent users guide.
Formatted to print at 8½ by 11 inches.
Twelve pages, 1.8 megabyte pdf

Copyright © 2005 by Sean Brady. Used here with permission. Not for other publication, distribution, nor resale. Copyright © 2005 by Sean Brady. Used here with permission. Not for other publication, distribution, nor resale.

Hugo Winterhalter confers with Billy Eckstine during a recording session.

Lena Horne, in what appears to be the same studio.

Mr. Robert Van Dyke thoughtfully provided us with this announcement from Page 10 of the November 1949 issue of Audio Engineering, in which we see the exact date of the change of responsibility for selected audio products from the Western Electric Company to the Altec Lansing Corporation.

Gladys Knight in 1954 at the age of nine or ten, and already with The Pips.

Microphone courtesy of Jeff Rudisill

Microphone courtesy of Jeff Rudisill

Photo courtesy of Dennis Schrank

Photo courtesy of Dennis Schrank

Photo courtesy of Dennis Schrank

Photo courtesy of Dennis Schrank

Photo courtesy of Dennis Schrank

Photo courtesy of Dennis Schrank

Download the specification sheet for this mic.