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The development of the modern microphone has its origins in telephone technology, which can be traced back to the mid-1800s. The term “microphone” was initially introduced by Wheatstone around 1827, referring to a purely acoustic device he had created, akin to a stethoscope, designed to amplify faint sounds. Its etymology stems from Greek, where “micro” signifies small and “phon” denotes sound.
Interestingly, this term was not initially used to describe telephone devices in general, which were instead referred to as “transmitters.” This nomenclature persisted through Western Electric’s professional microphone production until the 1940s. Today, we’ll look into 12 microphones that changed broadcast history.
The microphones showcased in this article are components of a collection consisting of around five hundred microphones, gathered over a span of twenty-five years through trades and acquisitions. This collection ranks as the second-largest in the country, and every microphone within it has been meticulously restored to its utmost original factory working condition and appearance.
During the early 1920s, the growing demands of broadcasting prompted Western to undertake the development of a more reliable and higher-quality carbon transmitter. A significant step in this direction was achieved with the introduction of the 369 and 373 models, featuring push-pull designs mounted within distinctive ring mounts and eye-catching protective cages. Notably, a double-button microphone from this line even made its way into President Warren G. Harding’s Inaugural Address in 1921.
As the mid-twenties approached, the 387 model emerged as a pinnacle of push-pull design excellence, characterized by its gold-sputtered diaphragm measuring just 0.0017 inches thick and crafted from duralumin. This model was succeeded by the slightly improved model 600 in the early thirties, and the double-button microphone became internationally recognized as the broadcasting industry standard.
The concept of a condenser transmitter has been present since the early days of telephone technology. However, due to its high impedance and low output, it remained impractical for early applications. The breakthrough came in 1915 with the development of the vacuum tube amplifier, which resolved the impedance and output limitations. In 1917, E. C. Wente of Bell Labs pioneered the first modern condenser microphone.
Initially, these early microphone models were not exceptionally reliable and were primarily reserved for acoustic research purposes. As we moved into the mid-1920s, there were notable improvements in condenser microphone designs. By the late 1920s, Western Electric had introduced six different models of condenser microphones: the 7A and 9A, often referred to as “mantle clocks,” the 8A and 10A floor-standing models, and the hanging cylinder models of the 47A and 53A.
These microphones all featured Wente’s renowned 394 condenser transmitter head, equipped with an aluminum alloy diaphragm. However, American-made condenser microphones gradually faded from the market by the mid-1930s.
In early 1931, Western Electric introduced the 618 electrodynamic transmitter, marking the debut of the dynamic microphone. Although the concept of a moving-coil microphone had been around since the late 1800s, it wasn’t until the advent of the vacuum tube amplifier and the use of cobalt permanent magnet materials that it became a practical reality.
At a time when the audio landscape was dominated by noisy carbon transmitters and often problematic condenser microphones, both of which required external power sources, the 618’s promise of a compact and trouble-free microphone garnered immediate success. In the mid-1930s, Western Electric further refined this concept with the iconic 630A “8 Ball” design. The dynamic microphone subsequently solidified its position as a cornerstone of American microphone production.
During the late 1920s, Dr. Harry F. Olson at RCA initiated the development of the ribbon microphone, initially experimenting with field coils and subsequently with permanent magnets. In 1931, approximately nine months following the introduction of Western’s 618 dynamic microphone, RCA introduced its very first permanent magnet bi-directional ribbon microphone, known as the 44-A.
The ribbon microphone’s pleasingly smooth sound and attractive design quickly established it as a broadcasting mainstay, a reputation it maintained well into the 1940s. In the mid-1930s, the design was enhanced with improved magnet materials, resulting in the 44-B and 44-BX models.
These microphones went on to exert a profound influence on microphone technology, remaining in production until the mid-1950s. This high-quality ribbon microphone continues to be in demand today and boasts one of the most iconic and recognizable designs worldwide.
In the early 1930s, Dr. Olson recognized the necessity for a directional microphone and subsequently developed the 77-A unidirectional model. This distinctive round microphone design evolved through a series of seven different iterations. The A, B, and C models employed dual ribbons that combined a pressure unit with a velocity unit to achieve the desired unidirectional pattern.
With advancements in magnet materials, the B model marked a significant reduction in size. The C and D models introduced the capability for multiple patterns. Notably, the 77-D and DX single-ribbon models, which emerged after World War II, could arguably be considered RCA’s most successful microphones.
They remained in production until 1973 when RCA ceased all microphone production. Graphic artists routinely depict this microphone’s widely recognized shape to signify public speech and can still be seen today on shows like Larry King and David Letterman.
During the late 1930s, Western Electric took a unique approach by delving into ribbon technology, resulting in the creation of the first switchable multi-pattern microphone. This innovative design combined the well-regarded 630A omnidirectional dynamic component with a distinctively crimped bi-directional ribbon assembly.
Like all preceding Western microphones, except for condenser types, it maintained an output impedance of 50 ohms. This microphone offered users a choice of three patterns: R (ribbon/bi-directional), D (dynamic/omnidirectional), and C (cardioid or a combination of patterns). Later, the 639B expanded on these options by introducing an additional three variations of combined patterns, bringing the total to six selectable patterns.
In the early 40s, Electrical Research Products Inc. (ERPI), a division of Western Electric, reimagined the acoustic enclosure of the 639 microphones specifically for use in motion pictures. This modified version was designated as the RA-1142 transmitter.
The history of the Shure Unidyne microphone traces back to 1937 when Ben Bauer embarked on a quest to develop a simpler and more dependable directional microphone that utilized a single element. Bauer’s breakthrough came when he employed time delay networks to manipulate sounds reaching the rear openings of the microphone, a system referred to as “uni-phase” by Shure.
This innovation allowed him to achieve controlled cancellation and generate a cardioid pattern. In 1939, Shure unveiled the Model 55A (30-50 ohms), Model 55B (200-250 ohms), and the high-impedance Model 55C microphones. During the 1940s, Shure expanded its lineup to include the shock-mounted broadcast models, 555 and 556. In 1951, the compact Unidyne microphone made its debut.
It’s remarkable to consider that there are few microphones, based on their original concept and design, that have maintained continuous production as long as some iteration of the Unidyne. In fact, its design is one of the three most iconic microphone shapes ever created, the other two being the RCA 44 and 77.
The genesis of the 640A/AA condenser microphone arose from Western Electric’s necessity for a dependable calibration microphone, coupled with the realization that the 394 condenser microphone was excessively large and unwieldy for the task. In 1932, a compact condenser microphone system featuring a one-inch diaphragm, initially known as the D96436, underwent successful testing and was subsequently rebranded as the 640A.
In 1942, Bell Labs uncovered a susceptibility of the 640A to variations in ambient temperature, pressure, and relative humidity during testing. To mitigate this issue, they made critical modifications, including changing the capsule diaphragm material from aluminum alloy to highly corrosion-resistant steel and adjusting other internal components. This revamped version was designated as the 640AA.
The 640AA swiftly became the preferred calibration microphone for professionals in the audio industry, including notable entities like RCA, Altec, and, notably, the National Bureau of Standards. Eventually, Western Electric determined that due to the limited demand for calibration microphones, procuring them as needed rather than manufacturing them in-house made more sense.
As a result, they entrusted the production of calibration microphones to Brel Kjaer, who crafted the 4160 microphones to fulfill Western Electric’s requirements. With the introduction of the 4160, the production of 640AA capsules ceased.
In 1928, Georg Neumann and Co. was established. Neumann’s inaugural venture into condenser microphones resulted in the CMV3, equipped with an REO84K triode amplifier and a pressure-omnidirectional capsule known as the M1/M2, which was meticulously crafted from hand-cast, gold-plated PVC.
In its earliest iterations, the diaphragms were created using a resin dissolved in alcohol and cast on water. Over time, PVC dissolved in amyl acetate was employed and cast onto gold-dusted plates for diaphragm production.
By 1932, Neumann had introduced a variation of the CMV3, known as the CMV3A, which allowed users to attach various condenser heads. Drawing inspiration from a 1927 German patent by Braunmuhl and Weber, Neumann pioneered the double-membrane capsule featuring a shared backplate. Within this backplate, 153 meticulously hand-drilled and strategically positioned holes, some penetrating the rear side, were incorporated.
This design achieved sound cancellation reaching the rear of the capsule, resulting in the creation of a cardioid pattern. This groundbreaking capsule was designated as the M7, marking the birth of the first cardioid microphone. It’s worth noting that the initial microphone with directional characteristics was Olson’s bi-directional ribbon microphone, designed between 1929 and 1930.
Subsequently, Neumann introduced the M8 bi-directional and M9 omnidirectional capsules. Remarkably, the M7 capsule design has remained in continuous production since its inception, holding an unrivaled influence over modern condenser microphone technology. Today, an updated version of the CMV3A bottle microphone, crafted by B.L.U.E. Microphones, continues to be in production.
Following World War II, Neumann reorganized his company and embarked on the development of the U-47 microphone, which was first introduced to the market in June 1948. Distribution was handled by Telefunken, which promptly affixed its name to the amplifier housing.
The U-47 marked a significant milestone as the first switchable-pattern condenser microphone, offering both cardioid and omnidirectional patterns.
It featured the highly successful 12-micron-thick M7 capsule and VF-14 tube amplifier, a metal-clad pentode configuration from the pre-World War II era adapted to function as a triode. The hand-selected VF-14 tubes featured a 55-volt filament designed to operate at 36 volts, extending tube life and ensuring quieter operation.
In the early 1950s, Mercury Records prominently promoted the U-47 as its “Living Presence” microphone, even featuring pictures of it on record jacket covers. By 1956, Neumann was able to reduce the microphone’s length by nearly three inches, thanks to advancements in capacitor technology. The U-47 also underwent cosmetic changes, with the capsule finish transitioning from chrome to matte to match the microphone’s overall appearance.
In 1956, the U-48, a cardioid/bi-directional version, was introduced. Two years later, Neumann assumed the distribution of its own products from Telefunken, restoring the Neumann logo. Gotham Audio took on the role of its North American distributor. In 1960, Neumann decided to update the U-47 with the U-67, originally designated as the U-60 but later renamed to emphasize its connection to the U-47.
The U-67 featured a capsule design shift from PVC to Mylar film, and the membrane was secured with a tensioning ring and screws instead of glue. Long-standing issues like proximity effect and overload during close work were resolved through the integration of a clever internal 40-Hz cutoff filter and an amplifier pad switch, allowing users to choose between close-up or distant use.
Additionally, a three-pattern switch was incorporated for added versatility. Efforts were made to minimize capsule resonance with a new tapered capsule windscreen, and the modern EF 86 tube enabled a more streamlined and tapered body design. This distinctive shape not only endured in Neumann’s microphone lineup but also influenced the designs of competing microphones still in use today.
In 1949, Dr. Herbert Grosskopf, working with the IRT (Institute Fur Rundfunktechnic, a German-based technical standards, and design organization established post-World War II by German broadcasters), conceived and patented the pioneering electronically remote-controlled variable-pattern condenser microphone known as the M49. Neumann was entrusted with the task of manufacturing this design, and it incorporated its established M7 capsule into the microphone.
Additionally, the IRT sought to establish a standardized tube amplifier for all German broadcast microphones, leading to the development of a special low-noise, handcrafted tube known as the Hiller MSC2. Telefunken subsequently manufactured the final iteration of this tube, designated as the AC701K.
Eventually, this tube became the standard for all condenser tube microphones within the German broadcast system. The “M” designation preceding the model number indicated the standard AC701K amplifier, while the “U” designation signified alternative tube amplification. A notable feature of the microphone was the distinctive taper of its windscreen grille, a deliberate effort to mitigate the impact of grille resonance.
The M 50, a sibling microphone resembling the M 49, shared the same design shape and employed the AC701K tube. However, it was designed specifically as a pressure microphone for distant orchestral recording. Its small pressure capsule underwent three iterations of diaphragms: first PVC, then aluminum (similar to the KM53), and ultimately gold-sputtered Mylar.
The diaphragm was flush-mounted within a plastic sphere, designed to enable the capsule to exhibit some directional characteristics in frequencies above 1 kHz while retaining an omnidirectional characteristic at lower frequencies. An additional +5 dB boost in high-frequency response was integrated into the AC701K tube amplifier circuit, resulting in a favorable overall frequency response when the microphone was employed at a distance from the sound source.
AKG, an abbreviation for Akustische und Kino-Gerate (Acoustic and Film Equipment), was established in 1947 in Vienna, Austria. In 1953, AKG introduced the C-12 condenser microphone, drawing inspiration from a dual backplate/dual-membrane concept patented by Kalusche and Spardock in 1951. This idea underwent modification and evolved into the CK-12 capsule.
Notably, AKG was the pioneer in manufacturing a split-electrode microphone. The original capsule membrane employed in the C-12 was constructed from 10-micron-thick PVC, and later transitioned to 9-micron-thick Mylar. The amplifier design was based on the 6072 tube, and the C-24 stereo edition of the microphone, featuring two CK-12 capsules, maximized the potential of this dual triode tube.
Similar to the M 49, the C-12 offered remote pattern selection capabilities, allowing users to switch between omni and bi-directional patterns using a selector switch located in a unit between the microphone and the power supply. Production of the C-12 continued until 1963. In 1964, the C-12A was introduced, featuring a 7586 Nuvistor tube amplifier and showcasing a physical design that foreshadowed the appearance of the 414 Series.
In 1959, after Telefunken withdrew the distribution of the U 47, they enlisted AKG to develop a large-diaphragm condenser microphone, resulting in the creation of the ELAM 250. This design incorporated the CK-12 capsule within a broader body featuring a sturdier wire mesh grille. A two-pattern selector switch (cardioid to omnidirectional) was integrated into the microphone.
The ELAM 251 expanded on this by adding a third bi-directional pattern to the switching options. The “E” designation following the 251 indicated export models, which employed a 6072 tube amplifier, while non-E designations featured the standard German AC701K tube amplifier. Both the C-12 and ELAM 250/251 microphones gained immense popularity, making them the most sought-after and expensive vintage tube microphones available on the market today.