Western Electric 639B
A dual-element microphone that put six pickup patterns behind one switch and spent two decades as the reference standard in broadcast and motion picture sound.
Overview
The 639B weighs three and a half pounds and stands seven and a half inches tall including its plug. The body measures three and a half inches wide by four and a half inches deep. It's instrument gray and built to sit in a studio, not a suitcase. The number to remember is six: the 639B has six directional patterns, selectable with a switch, ranging from cardioid through figure-eight to omnidirectional. The earlier 639A gave engineers three patterns. The B doubled that, and the flexibility is what kept the design in service across recording, motion picture, and broadcast work long after most of its contemporaries had been retired.
The microphone's origins trace back to Bell Laboratories, which developed the original 639 design. According to Altec's own 1965 documentation, the 639 remained a recognized standard in recording, motion picture, and broadcast for two decades. That's a long run for any piece of audio equipment, and this one has a mechanical ribbon element inside. The design has two independent elements, one dynamic and one velocity (ribbon), carefully phased and acoustically integrated to produce what the manufacturer described as the finest poly-pattern microphone in current manufacture. That's marketing language, but combining a moving-coil dynamic element with a ribbon in a single housing was genuinely uncommon and needed careful acoustic matching to work properly.
The frequency response is rated at 40 to 10,000 cycles, which reflects its era and its intended job. This isn't a microphone for capturing the full harmonic spectrum of a symphony orchestra in a modern recording. It's a voice and dialogue tool built for the speech band and the lower musical registers. Output impedance is 30/50 ohms, and output level is rated at -52 dBm per 10 dynes/cm². Hum is specified at -120 dB referenced to 10⁻³ Gauss, which points to the magnetic shielding around the ribbon element. That matters on any velocity microphone, since ribbon elements are inherently sensitive to stray magnetic fields. The instrument gray finish is utilitarian, and the two-stage wind screen protects against plosives and breath noise without, presumably, hurting the frequency response too much.
Altec's documentation describes the 639B as sometimes known as a "super cardioid" because of its high front-to-back pickup ratio in the midrange, the region that counts for speech intelligibility. That directional control is the microphone's defining characteristic. In a broadcast studio or on a film set, rejecting off-axis sound is often more useful than a flat frequency response. The six-pattern switch let engineers adapt the pickup to the room, the talent, and the noise environment without swapping microphones. The same document notes that the 639's quality contributed to Academy Awards for outstanding sound on a number of motion pictures. That's difficult to verify independently, but it fits the microphone's long tenure in Hollywood.
Mix (October 1997, p.46) traced the lineage of condenser microphones back to E.C. Wente's work at Bell Labs in 1917, and the same corporate research culture that produced the first modern condenser also produced the 639. The dual-element approach was a distinctly Western Electric solution to a problem other manufacturers solved differently. Shure, for instance, introduced its own unidirectional microphones in 1939, the same year Western Electric did, according to Audio (December 1974, p.86). The 639B is the Bell Labs approach: complex, over-engineered, and capable of results that simpler designs struggled to match.
The 639B is not convenient. There's no phantom power requirement, since it's a passive dynamic/ribbon design, but the ribbon element makes it more fragile than a pure dynamic microphone, and the two-stage wind screen adds bulk. The 30/50 ohm output impedance is low by modern standards but was standard for the era, and it requires a matching transformer or a preamp designed for low-impedance inputs.
That's advertising copy, not an independent verdict, but in difficult acoustic environments pattern control is the most direct tool an engineer has. The 639B gave them six of them.
The 639B isn't rare or obscure. It was produced in large numbers and saw wide use. It does have a Bell Labs association, a role in the motion picture industry, and an unusual dual-element design. Prices vary considerably depending on condition, completeness, and whether the ribbon element is intact.
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