In almost every phone, laptop, and cheap headset you have ever held up to your face, there is a descendant of a single laboratory sample—a brass disc with 200 holes and a polymer film, a quarter-thousandth of an inch thick, stretched over it. This is the story of how two engineers solved a problem the industry did not consider urgent—and in the end reshaped audio input across all consumer electronics.
By the end of the fifties, the world of sound recording and transmission resembled a menu with four dishes, each of them disappointing in its own way. Carbon microphones—the workhorses of telephony since the late 19th century—were cheap and durable, but their frequency range remained narrow, while their characteristic hissing background made recording music unthinkable. Dynamic microphones delivered decent quality onstage and in radio studios, yet their coil and magnet imposed a certain minimum size and weight; fitting such a capsule into a pocket recorder would have been an engineering feat with no practical point. Piezoelectric crystal models were more compact, but fragile and temperamental when it came to temperature and humidity—a Rochelle salt crystal could literally dissolve in its own sweat at high humidity.
And at the summit of quality stood the condenser microphone—essentially a sensitive capacitor with one movable plate serving as a diaphragm. The principle was elegant: a sound wave vibrates the diaphragm, capacitance changes, and the electrical signal reproduces the shape of the sound with high fidelity. The problem lurked in the details: for the capacitor to work, a constant polarizing voltage had to be maintained between the plates—usually from 48 to 200 volts. That meant an external power supply, a thick cable, additional circuitry. The condenser microphone remained a tool for studios and broadcast stations, where its cost and bulk were justified by impeccable sound. For the mass consumer, it was about as accessible as a Steinway grand piano for a school choir.
AT&T—the parent company of Bell Telephone Laboratories—controlled the United States telephone network at the time and was perfectly comfortable with carbon microphones in its handsets. A carbon capsule cost pennies, lasted for years, and none of the subscribers complained that voices did not sound “studio-quality.” Why spend resources replacing something that works? This question is one of the most insidious in the history of technology: it sounds sensible right up to the moment someone finds a better solution and the market shifts irreversibly.
In 1960, Bell Labs management gave two researchers a specific engineering assignment: create a microphone that would be compact, rugged, and cheap. James Edward West, born February 10, 1931, an African American physicist from Virginia, had already spent several years at the laboratory working on acoustic problems. Gerhard Martin Sessler, born four days later—February 15, 1931—in Germany, was a specialist in electroacoustics and dielectric physics. Their partnership proved remarkably productive: Sessler brought a deep understanding of how charged materials behave; West, engineering intuition and the persistence of an experimentalist.
The key idea they arrived at was not a flash from nowhere. The very concept of an electret—a material capable of retaining a permanent electrical charge much as a magnet retains a magnetic field—had existed for a long time. The term was introduced by the British physicist and engineer Oliver Heaviside back in 1885, drawing a direct analogy: if there is a permanent magnet, why should there not be a permanent “electret”? For decades, electrets remained a laboratory curiosity. Wax and ceramic samples lost their charge too quickly, were unstable when heated, and practically useless for serious engineering. Attempts to use them in microphones had been made since the 1920s, but every time they ran into the same wall: the charge degraded, and within a few months the device turned into a dead capacitor.
West and Sessler placed their bet on a new class of materials—fluoropolymers. A thin film of polytetrafluoroethylene—the very Teflon used to coat frying pans—or polyethylene terephthalate—Mylar—had a property that changed the entire picture: once properly polarized, it retained its electrical charge for years and decades. The molecular structure of fluoropolymers—dense, chemically inert, with extremely high resistivity—did not allow the charge to “leak away.” A wax electret was a candle destined to melt; an electret made of Teflon film turned out to be something like a granite monument.
The process of creating an electret diaphragm, described in the patent, is beautiful in its own straightforward way. A polymer film 0.25 mil thick—about 6.35 micrometers, ten times thinner than a human hair—was placed between two electrodes separated by a gap of around 3 millimeters. A DC voltage of roughly 3500 volts was applied to the electrodes—a powerful electric field literally pressed charges into the surface of the polymer. At the same time, the film was heated to approximately 120 °C and held at that temperature for 15 minutes. The heat softened the molecular structure, allowing the charges to penetrate deeper. Then the film was slowly cooled, and the polymer matrix “froze” the charges in place—like an insect in amber.
The result—a metallized film with an electrical field “stitched” into it—became both diaphragm and source of polarizing voltage at once. It was stretched over a perforated backplate—in the early samples, a brass disc about 36 mm in diameter and 1 mm thick, with roughly 200 holes. The holes were needed so air could pass freely through the backplate: without them, the air cushion between the diaphragm and plate would act as a damper, quenching vibrations and killing high-frequency sensitivity.
When a sound wave struck the diaphragm, the distance between the charged film and the backplate changed. The capacitor’s capacitance oscillated in time with the sound. Since the charge on the electret remained constant, the changing capacitance produced a changing voltage—an electrical signal precisely copying the shape of the sound wave. Roughly speaking, the microphone worked on the same principle as a conventional condenser microphone, but carried its own “power supply” inside it—in the form of a charge frozen solid in place. External high-voltage power was no longer needed. There remained only the need for a miniature field-effect-transistor preamplifier, because the output impedance of the electret capsule was very high—but that was already a problem an order of magnitude simpler and cheaper.
What still amazes me is the elegance of this solution: the whole trick lies in fifteen minutes of heating and several thousand volts, after which the film remembers its charge for decades.
On May 22, 1962, West and Sessler filed for patent US 3,118,022. The patent was granted on January 14, 1964. The document described the design of a foil electret microphone in exhaustive detail—from the chemical composition of the film to the geometry of the backplate perforations. It would seem that the parent company, AT&T, should have seized on the invention: here it was, the future of telephone communication, a microphone that could cost pennies in mass production. But the reaction was cool.
AT&T’s logic was rational in its own way. The company owned a monopoly on the telephone network and produced handsets by the million. The carbon microphone in each of them cost next to nothing. Switching to a new technology would have meant replacing production lines, retraining staff, testing reliability in the field—and all of it for better sound quality that subscribers did not demand. The telephone network already limited bandwidth to 300–3400 hertz; putting a microphone with an extended range into it was like filling a lawnmower with premium gasoline. AT&T put the electret microphone on the shelf. Sixteen years would pass before the company released its own model—EL2—for push-button telephones, and that would not happen until 1978.
It seems to me that this episode is the quintessence of how large corporations handle breakthrough technologies: if an invention threatens not a competitor but their own well-oiled production system, it is easier to ignore. Still, the patent was published, and the world beyond AT&T proved more receptive.
The first company to truly appreciate the electret microphone’s potential for the mass market was Japan’s Sony. In 1968, Sony began incorporating electret condenser microphones into its consumer products. The decision was technically obvious: an electret capsule required no high-voltage supply, could run from a battery through the simplest transistor stage, weighed only grams, and still provided a frequency response unattainable by carbon and piezoelectric counterparts. For portable audio equipment—cassette recorders, which Sony was actively developing—it was an ideal combination.
The Sony TC-55 cassette recorder, released in 1972, became one of the notable examples of integrating an electret microphone into a compact device. Its built-in microphone made it possible to record speech without external accessories—all you had to do was press a button. For journalists, students, and businesspeople, this changed the very practice of working with sound: the voice recorder ceased to be a professional instrument and became an everyday object. Japanese manufacturers—Sony, Panasonic, and others—quickly scaled up production of electret capsules, and the unit price plummeted. By the mid-seventies, the electret microphone had begun making its way into hearing aids, intercoms, public-address systems, and answering machines.
A technology’s path from laboratory to mass product often runs through other people’s hands. West and Sessler created the principle and the prototype; the Japanese electronics industry created the scale. Neither could have existed without the other—but giving all the credit to one side alone would be a distortion. By the eighties, electret microphones accounted for the overwhelming majority of all microphones manufactured in the world—by some estimates, up to 90 percent of the total. The figure is deceptively impressive: it reflects unit volume, not the cost or importance of each individual unit.
It would be wrong to claim that the electret microphone displaced every other type. Studio recording continued—and continues—to use conventional condenser microphones with external phantom power: their noise characteristics, dynamic range, and tonal coloration remain unmatched for mission-critical work. Shure SM58 and SM57 dynamic microphones, which became the industry standard for live sound, never left the stage. Ribbon microphones experienced a renaissance in the 2000s thanks to the fashion for “warm” vintage sound. Every microphone type occupies its own niche, determined by the physics of conversion and the specific demands of the application.
The electret microphone won where size, price, and “good enough” quality were the deciding factors. A telephone handset, a call-center headset, a laptop’s built-in microphone, a child’s walkie-talkie, a home security system—in all these devices, the electret capsule proved to be the optimal compromise. When mobile phones became a mass phenomenon in the late nineties and 2000s, it was electret microphones that provided voice input in the overwhelming majority of models. Later, in the smartphone era, MEMS microphones—microelectromechanical systems manufactured using semiconductor lithography techniques—began taking over part of the market. But MEMS technology, in essence, solved the same task West and Sessler had set for themselves: a miniature, cheap, sufficiently sensitive converter of sound into an electrical signal.
The counterfactual question—what would have happened without the electret microphone?—requires caution. Miniature electronics would have developed in any case: transistors, integrated circuits, lithium-ion batteries—none of that depended on acoustic transducers. Piezoelectric PVDF films, MEMS technology, improved dynamic capsules—alternative paths existed. But each would have required more time to refine or would have cost more to manufacture. The mass spread of cheap built-in microphones would probably have been delayed by several years, while some products—such as the first portable voice recorders or cheap telephone headsets—might have appeared in a different form, or not appeared at all in the price bracket that made them everyday objects.
In 1999, James West and Gerhard Sessler were inducted into the National Inventors Hall of Fame—an honorary recognition that places them alongside Thomas Edison and the Wright brothers. In 2006, West received the National Medal of Technology, one of the highest honors awarded by the U.S. government for contributions to innovation. These distinctions, however, did little to change public perception.
The paradox of infrastructure inventions is that they become invisible precisely because of their success. Someone speaking on the phone does not think about the microphone—just as they do not think about the composition of the plastic casing or the alloying of copper in the wires. The electret microphone became so ubiquitous, so ordinary, that it stopped being perceived as technology. It turned into air—in the literal sense, because it is through it that vibrations in the air enter the electronic world.
James West—an African American engineer who grew up in the era of segregation, received an education despite systemic barriers, and worked at Bell Labs for decades—remained a figure virtually unknown beyond the professional community. His surname did not become a household name, his face did not appear on magazine covers, his invention was not associated with his name. Sessler, who returned to Germany and continued an academic career at the Technical University of Darmstadt, was well known within the narrow circle of electroacousticians, but just as invisible to the general public. Two people whose work quite literally gives voice to the daily lives of billions remain in the shadow of their own invention—and that is perhaps the clearest indication of how deeply their technology has grown into the fabric of the modern world. Every time you say “Hello” into a telephone handset, there is a high probability that your voice passes through a descendant of that very charged film from the laboratory in Murray Hill, New Jersey—and neither you nor the person on the other end gives it a thought.