Looking back
Apr 1, 1999 12:00 PM, R. David Read
The first recorded use of the term microphone was in 1827 when Sir Charles Wheatstone described a mechanical vibrating stethoscope. It would be 50 years before anything closely resembling what we now call a mic appeared on the audio scene.
As most students are taught, Alexander Graham Bell discovered the principles of telephony and filed for a patent on his invention at the U.S. Patent Office in Washington D.C on the morning of February 14, 1876. The mention of the word "morning" is significant, since later that day Elisha Gray (the Gray in GrayBar) filed with the U.S. Patent Office expressing the intent to proceed with the development of his conception of the telephone.
Interestingly, both Bell's and Gray's experiments initially aimed to resolve a telegraphic problem. The commercial telegraph services in the United States came into being in 1844, and while commercial development was slowed during America's War Between the States, the telegraph companies expanded rapidly after that conflict. However, it was still only possible to send one (one-way) message over one wire. Hence, if a telegram were being sent to Boston from New York, and a simultaneous transmission of another telegram from Boston to New York were required, another wire would be needed.
This limitation gave rise to considerable experimentation aimed at the development of a harmonic telegraph, i.e., a method whereby telegrams could be sent using different tones over a common wire-what we now call multiplexed technology. Fortunately, at least for the audio industry, radio had yet to be invented; consequently, experiments in harmonic telegraphy employed audible tones. It was in conducting experiments on the harmonic telegraph that Bell stumbled onto the rudimentary principles of telephony. As Bell's biographer Robert Bruce remarked, "The telephone was born, and its wise father knew his child."
Both Bell and Gray had been preceded in the conception and construction of equipment that could have been adapted into a telephone transmitter.
A young French electrician Charles Bourseau prophesied in 1854 that the principles of the electrical telegraph might be used to transmit the spoken word. He wrote, "Suppose that a man speaks near a movable disk, sufficiently flexible to lose none of the vibrations of the voice; that this disk, alternately makes and breaks the connection with a battery; you may have at a distance another disk which will simultaneously execute the same vibrations."
There is no evidence that Bourseau ever constructed such equipment. However, at the conclusion of his paper he muses, "I have made some experiments in this direction. They are delicate, and demand time and patience; but the approximations obtained promise a favorable result."
Credit for the first (albeit crude) "telephone" goes to the German inventor Philipp Reis and his introduction of a speech-transmission apparatus. This device, however, relied on the "make-break" characteristics common to DC telegraph circuits.
In the legal battles that bespoke the "Telephone Wars," which broke out almost immediately after Bell's introduction of his telephone, it was made clear that the principle that set Bell's invention apart from Reis' was Bell's use of an audio signal to modulate a constant DC circuit.
The telephone transmitter In telephone lexicography, the send side of a telephone (i.e., that part of the instrument into which one speaks) was termed to be a transmitter, a distinction that continues today. The British inventor David Hughes used the word microphone to describe his discovery of a carbon button transmitter using a multiple loose contact.
Hughes' introduction earned him the wrath of Thomas Edison, who laid claim to the invention of the double-button transmitter. Edison maintained that he had laid claim to the invention some two months prior to Hughes' announcement. Accusing Hughes of piracy, Edison brought to bear all the blame that he could place on his opponents.
Refinements and improvements to the carbon button telephone transmitter came quickly in the years from 1878 to 1882. In testimony to these earlier developers, the carbon-button transducer, the essential element in millions of telephones in service around the globe, remains basically unchanged.
As their predecessors had focused their attention on improvements to the telegraph, experimenters of the era were predisposed to seek more reliable and efficient components for the fast-growing telephone industry.
The moving coil (dynamic), piezoelectric (crystal) and the electrostatic (condenser) were all posited by experimenters of the time as possible solutions to better electroacoustic transducers. The problem with all of these systems was their inability to amplify the minute output of the transmitters into a signal that could be deployed over increasing distances.
Acoustical recording In the realm of audio, if we may use that term to differentiate sound systems from their speech transmission brethren, the industry continued in an acoustic-mechanical mode. The carbon button mic, while adequate for speech transmission, was not adaptable for use in musical recordings. Hence, we might consider that the acoustical horns employed to record and play back phonograph records were the next version of the mic.
Audio amplification To address the next stage in development, we must again visit the telephone industry and Bell Telephone's research arm-the Western Electric Company. By 1911, long-distance telephone service had been established between New York and Denver. However, given the available technology, that was the farthest attainable distance of telephone transmission.
Frantic efforts were being made to establish transcontinental telephone service as a central exhibit of the 1915 Pacific-Panama Exposition to be held in San Francisco. Bell Telephone had acquired the rights to Lee de Forest's audion three-element vacuum tube in 1912; however, work continued on the development of an acoustic-mechanical microphonic repeater. There were some doubts as to whether the vacuum tube amp could be perfected to provide reliable service as a telephone circuit repeater. Service for the transcontinental system was established in time to meet the 1915 San Francisco deadline, but it employed paralleled microphonic and vacuum tube amps to augment each other in the event of failure. Thus, 1915 saw the dawn of electronic amplification.
New horizons for audio Western Electric recognized that the vacuum tube amp opened new areas of application. Loudspeaking telephones, what we now know as loudspeakers, made PA systems commercially viable. Experiments in this area were conducted in field tests before they were suspended for the duration of World War I.
Central to these developments was the work of Edward Wente, who had joined the staff of Western Electric in 1914. Using a principle that had been a laboratory curiosity for 50 years, Wente transformed the electrostatic transmitter into the first flat-frequency response mic. Wente called his invention a condenser transmitter. So, the condenser mic, still considered up-to-date technology, was actually introduced in 1916.
Wente continued to perfect the condenser mic until, by 1922, he had produced a device with 100 times the sensitivity of his 1916 model, making the condenser mic a commercially practical device.
After hostilities in Europe ceased, interest in the development of PA systems intensified. Both Western Electric and the Magnavox Company of Oakland, CA, vied for installations. When President Warren G. Harding dedicated the Tomb of the Unknown Soldier on November 11, 1921, thousands gathered at Arlington National Cemetery to hear his address over a Western Electric supplied PA system, while thousands more heard his speech transmitted over telephone lines to audiences at Madison Square Garden in New York and the Cow Palace in San Francisco.
The '20s were a heady time for the fledgling sound reinforcement industry: Radio broadcasting had captured the imagination of countless avid listeners; Warner Bothers, in concert with Western Electric, had introduced a workable synchronized film/audio playback system; large audiences in stadiums and auditoriums could be addressed with PA systems; and disc recording companies had finally been persuaded to adopt electronic amplification.
Mic improvement All of these developments necessitated the development of more reliable, improved mics with better fidelity. Concepts were advanced that provided more directional control of the mic's pickup pattern and improved the instrument's sensitivity.
Western Electric, through its wholly owned subsidiary ERPI (Electrical Research Products Inc.), had established a strong relationship with Warner Brothers Studios, and by virtue of cross-licensing agreements, had a majority position in the motion picture studios and theatres across America.
Condenser mics of that era, while commercially successful (having been tamed by the introduction of directional patterns), still exhibited some serious drawbacks. The high-impedance output of the capacitor element necessitated that the preamp be located within centimeters of the element. Vacuum tube amps were still, in respect to today's transistor circuits, large and difficult to house in unobtrusive mic cases. An external power supply was required to provide working voltages for the vacuum tubes. To circumvent some of these difficulties, Western Electric introduced the first high-quality moving-coil (dynamic) mic in the late '20s.
Others, notably C.B Sawyer and C.H Tower, perfected the crystal electromechanical transducer for use as a mic. Crystal (piezoelectric) transducers had been a known quantity since the turn of the century; however, the scarcity of high-grade quartz crystal stifled development of this technology. Sawyer and Tower solved the dual problems of growing sufficient quantities of Rochelle salt and ensuring that the salt was pure enough to be practical in the manufacture of mics. Crystal mics were used briefly in some of the motion picture studios, but the incompatibility of Rochelle salt and high temperatures made their use in the intense lights of a studio impractical.
Piezoelectric transducers, however, went on to become useful devices in phonograph pickups, telephone receivers and the production of commercial grade mics for the communications industry.
Ribbon Mics Meanwhile in Germany, between 1923 and 1926, Schottky and Gerlach of Siemens developed and patented a method whereby a single metallic ribbon could be substituted for the multi-turn voice coils in loudspeakers. The development produced a mildly successful loudspeaker, but more importantly, it stirred the interest of Harry F. Olson at RCA. Olson saw the development for possible use as a diaphragm for a pressure-gradient, bidirectional mic, and the ribbon mic was born.
Ribbon mics were introduced by RCA in various versions between 1931 and 1941. They exhibited extremely good frequency response, outstanding sensitivity and had the notable advantage of having a bidirectional pickup pattern. The downside was that they were extremely fragile and could only be used in very controlled environments.
Ribbon mics enjoyed great popularity in the broadcast and recording field for many years. In addition to RCA, ribbons were manufactured by Shure Bothers and some European producers, notably beyerdyamic.
Directivity control The next notable development in mics was the marriage of the ribbon element and the moving-coil element into a hybrid mic. By varying the ratio of the ribbon to the moving coil pickup, a unidirectional pattern having the familiar cardioid shape was realized. The RCA 77B, introduced in 1937 and followed by the Western Electric 639A in 1939, was an example of such a hybrid unidirectional mic.
As sound reinforcement demands increased and multi-mic recordings became more prevalent, the need for more directionally controlled mics became increasingly evident.
The next evolutionary step was the development of single-element unidirectional mics. These developments took the form of modified mechanical case designs and internal damped pipes to introduce an acoustical delay to sounds arriving off axis to the front of the mic's diaphragm-be it a moving-coil or ribbon type. The Shure Brothers Unidyne Series (Dynamic 1941) and the RCA 77D type (Ribbon 1941) employed these principals.
Neumann, the German mic manufacturer, employed a controlled phase shift principal in the development of its popular unidirectional M49 electrostatic (condenser) mic. These principles were developed in the '30s but, owing to World War II, did not reach commercial introduction until 1953.
During the war, commercial development of mics on both sides of the Atlantic was temporarily suspended, though there were still some significant developments in electroacoustic transducers. The crystal (piezoelectric) transducers that had been developed by the British and French in 1917 for the purpose of locating such underwater objects as enemy submarines became the highly successful SONAR systems used during the 1939 to 1946 conflict. By 1950, the underlying principles of mic technology that we continue to use today had been firmly established.
The feature common to all available mics was a large, obtrusive size. Consequently, the next step in the evolution of mics was to shrink their size to make them more readily adaptable to handheld use. The mic cases began to take on a cylindrical shape, wherein the element was housed at one end of the cylinder. In 1954, Electro-Voice introduced this type of packaging in the Variable D series. Also in 1954, RCA started delivering a unidirectional ribbon version employing a similar packaging concept.
Altec-Lansing, who had previously seemed content to market the earlier Western Electric designed dynamic mics, took a serious interest in bringing to market a quality, small-sized condenser product. This resulted in a mic capsule measuring 1.6 cm in diameter and 1.0 cm in depth. The first commercial application of this new condenser capsule was in the Altec M11 System, which was publicized for its performance and its unobtrusive design.
Altec continued to exploit the small size of its M21 capsule and followed up with its Lipstick series, in which the entire mic (sans cable and power supply) measured only 3 inches (7.6 cm).
John Hilliard, chief engineer for Altec-Lansing, explained how the name came into being during an interview on NBC's "Hall of Science." He quipped, "Early in its (the M21) development, I used my wife's lipstick case to make an experimental model, and by comparison the size is practically the same."
Altec also used this capsule in a number of systems aimed at medical noise-control measurements and other nonentertainment audio applications.
Other mic manufacturers did exist in the United States; however, none of them were able either to achieve great stature or to penetrate into the studio market. American Microphone Company made a reasonably good dynamic but was absorbed by Electro-Voice in the mid '50s.
More advancements Continuing the trend toward further miniaturization, Electro-Voice made great strides in bringing forth lavalier type products during the '50s. These were wired devices, but they provided performers and other sound system users with a freedom of movement that hitherto had been impossible.
A short-lived product development was the acoustical line array or shotgun mic, in which a unidirectional (dynamic) was coupled to an acoustical tube ot rubes. These were used primarily in TV studios to extend the working range of the mic. They suffered from a rather poor frequency response and had a marginal directivity factor.
Accompanying the drive to reduce the size and weight of mics was a steady improvement in the materials and production processes. None of these developments was as sensational as some of the earlier breakthroughs, but better and more reliable products continued to appear. By 1960, polyester films started to replace metal alloy diaphragms in dynamic mics.
Wireless or radio-frequency (RF) mics started making an appearance in the early 1960s. These devices were not as much a refinement in mic technology as they were an improvement in transmission technology. The mic capsules were essentially the same capsules being used in conventional mics. The audio cable had been replaced by an RF link, allowing the user to have virtually unlimited mobility.
Unfortunately, many of the earlier models operated on the 36 MHz to 50 MHz band, which subjected them to a wide range of interference. They did not employ any form of limiting, and consequently could be easily overmod-ulated, causing distortion in the sound system. The vacuum tube receivers employed were characteristically unstable and subject to frequency drift. It would be a full two decades before the bugs could be sufficiently worked out of the RF transmission system, allowing performers and sound practitioners to rely on the wireless mic.
The development of the FET (field effect transistor) allowed for the practical construction of the electret condenser mic. Electret technology, wherein the external DC bias required for a convention condenser mic is eliminated, stems from an idea advanced 50 years earlier. By using a permanently polarized dielectric material, the device can be made self-contained using a readily available electrolyte battery to operate the FET. Electret technology had to wait 50 years until the materials to implement the idea became readily available.
In 1978, Crown International introduced its PZM (Pressure Zone Mics). Again, this was not so much a radical development in mic capsule technology as it was a truly innovative packaging design. To eliminate unwanted reflective signals from adjacent boundaries, the PZM has its capsule mounted in a manner that essentially prohibits the entry of sound pressure from adjacent reflective surfaces.
I have skimmed over such subjects as measurement/calibration mics, recording techniques such as are used for stereo and quadraphonic sound. The intent has been to concentrate on the development of the mic to the exclusion of its many varied applications.
I would, however, ask you to bear in mind that, as you place that state-of-the-art condenser mic on the stage, you are using a technology that Dr. Wente first brought to light in 1916.
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