Western Electric 618A (1931)

The first commercial dynamic microphone ever made. It was born in a lab, built for broadcast, and used by a president.

Overview

Early radio voices that didn't crackle like a campfire or drown in hiss often owed something to the Western Electric 618A. Western Electric released it in 1931. Engineers E.C. Wente and Albert Thuras developed it under the Bell Labs umbrella. It was the world's first commercial dynamic microphone. It moved audio capture away from the fragile, high-maintenance condenser and carbon granule mics and into something rugged, reliable and better sounding.

Radio was becoming mass media, public address systems needed to reach thousands, and recording demanded more fidelity than ever. The 618A was designed for "utmost fidelity of pick-up, inherent quietness, stability, and mechanical ruggedness" - a mouthful, but it meant you could set it up, turn it on and trust it. No polarizing voltage, no delicate membranes, no constant recalibration. A tough, compact housing held a moving coil system that performed consistently under real-world conditions.

It became the standard microphone for 1930s news conferences and a favorite among broadcasters. It was the mic Franklin Delano Roosevelt used for his Fireside Chats, even through crackling receivers. The 618A had presence, warmth, and a frequency response that covered the human voice from 35 Hz up to 9,500 cycles per second. For its time, that was extraordinary.

It was not a consumer gadget. It was a precision instrument, designed for professional use in radio, sound recording, and public address, and later found a home in film and television production. Its omnidirectional pattern made it forgiving in placement. Its high output meant it could drive early amplifiers without excessive gain stages, which reduced noise. It wasn't flashy, but engineers could leave it running all day without a second thought.

Specifications

Manufacturer	Western Electric
Type	Moving Coil
Directionality	Omnidirectional
Frequency response range	35 to 9,500 cycles per second
Electrical impedance at low frequencies	approximately 28 ohms with a phase angle of nearly zero degrees
Electrical impedance at 10,000 cycles per second	about 38 ohms with a phase angle of about 20 degrees
Output level	For a person speaking with normal conversational intensity at a distance of three feet, an output level of –84 dB relative to a zero level of six milliwatts is representative
Diaphragm material	thin duralumin
Magnet type	permanent magnet made from a high grade cobalt steel alloy
Coil material	aluminum ribbon

Key Features

Low impedance, high practicality

The 618A had a low electrical impedance, around 28 ohms at low frequencies, which made it far easier to interface with the amplifiers and transmission lines of the era. High-impedance mics lost signal over cable runs. The 618A could be used at distance without degradation. Its impedance rises slightly at higher frequencies, to about 38 ohms at 10 kHz, but the phase angle stays manageable, which helped keep performance stable across its range. In practice that meant fewer transformers, fewer points of failure, and a cleaner signal path from mic to transmitter.

No polarizing voltage? No problem

The 618A used a permanent magnet made from a high-grade cobalt steel alloy, so it needed no external power or polarizing voltage at all. That was a big deal. Condenser mics of the time, like Wente's own 1916 design, required careful voltage regulation and were sensitive to humidity and handling. The 618A sidestepped all that. Plug it in, speak, and it works. Engineers loved that. Broadcasters depended on it.

Velocity-driven output

The principle is simple. Sound waves hit a thin duralumin diaphragm, which moves an attached aluminum ribbon coil within a magnetic field. The motion induces a voltage proportional to the coil's velocity, hence a dynamic microphone. This design is inherently tougher than tensioned membranes or carbon chambers, and it gives a natural, full-bodied response, especially in the midrange where the human voice lives.

Engineered for the real world

Behind the scenes, the 618A’s acoustic design includes air chambers and slot openings that equalize pressure on both sides of the diaphragm. This isn’t just about frequency response—it’s about survival. Barometric shifts, temperature changes, even a sudden gust of air wouldn’t throw it off. The fact sheet notes it’s “not affected appreciably by temperature changes likely to be encountered in its use,” which meant it could live on a podium in a drafty hall or a studio with inconsistent climate control. And with its compact, tough housing, it could be moved, mounted, and handled without fear of damage.

Efficiency that mattered

The 618A was also efficient. Its output level, rated at - 84 dB relative to six milliwatts for normal speech at three feet, was high for its time. That meant less amplification was needed, which meant less noise. Compared to the conventional condenser mics of the day, the 618A offered better signal-to-noise performance in practical applications.

Historical Context

Radio was moving from hobbyist tinkering to mass communication, and telephony was demanding clearer, more reliable voice transmission. The carbon granule mics that dominated telephony were noisy and nonlinear. Wente's 1916 condenser mic was a leap forward in fidelity but finicky in practice. The 618A offered high fidelity without the fragility. Bell Labs developed it as telephone and radio technology advanced, to meet the growing demand for microphones that could deliver clear, consistent audio in real-world conditions.

It quickly became the standard for broadcasters and was widely adopted for news conferences, public address, and studio recording. When the president of the United States needed to speak to a nation, he didn't reach for an experimental mic. He used the 618A, which had already proven itself in studios and stations across the country.