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Looking back

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

Looking back

Apr 1, 1999 12:00 PM,
R. David Read

The first recorded use of the term microphone was in 1827 when Sir CharlesWheatstone described a mechanical vibrating stethoscope. It would be 50years before anything closely resembling what we now call a mic appeared onthe audio scene.

As most students are taught, Alexander Graham Bell discovered theprinciples 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. Themention of the word “morning” is significant, since later that day ElishaGray (the Gray in GrayBar) filed with the U.S. Patent Office expressing theintent to proceed with the development of his conception of the telephone.

Interestingly, both Bell’s and Gray’s experiments initially aimed toresolve a telegraphic problem. The commercial telegraph services in theUnited States came into being in 1844, and while commercial development wasslowed during America’s War Between the States, the telegraph companiesexpanded rapidly after that conflict. However, it was still only possibleto send one (one-way) message over one wire. Hence, if a telegram werebeing sent to Boston from New York, and a simultaneous transmission ofanother telegram from Boston to New York were required, another wire wouldbe needed.

This limitation gave rise to considerable experimentation aimed at thedevelopment of a harmonic telegraph, i.e., a method whereby telegrams couldbe sent using different tones over a common wire-what we now callmultiplexed technology. Fortunately, at least for the audio industry, radiohad yet to be invented; consequently, experiments in harmonic telegraphyemployed audible tones. It was in conducting experiments on the harmonictelegraph that Bell stumbled onto the rudimentary principles of telephony.As Bell’s biographer Robert Bruce remarked, “The telephone was born, andits wise father knew his child.”

Both Bell and Gray had been preceded in the conception and construction ofequipment that could have been adapted into a telephone transmitter.

A young French electrician Charles Bourseau prophesied in 1854 that theprinciples of the electrical telegraph might be used to transmit the spokenword. He wrote, “Suppose that a man speaks near a movable disk,sufficiently flexible to lose none of the vibrations of the voice; thatthis disk, alternately makes and breaks the connection with a battery; youmay have at a distance another disk which will simultaneously execute thesame vibrations.”

There is no evidence that Bourseau ever constructed such equipment.However, at the conclusion of his paper he muses, “I have made someexperiments in this direction. They are delicate, and demand time andpatience; but the approximations obtained promise a favorable result.”

Credit for the first (albeit crude) “telephone” goes to the German inventorPhilipp Reis and his introduction of a speech-transmission apparatus. Thisdevice, however, relied on the “make-break” characteristics common to DCtelegraph circuits.

In the legal battles that bespoke the “Telephone Wars,” which broke outalmost immediately after Bell’s introduction of his telephone, it was madeclear that the principle that set Bell’s invention apart from Reis’ wasBell’s use of an audio signal to modulate a constant DC circuit.

The telephone transmitterIn telephone lexicography, the send side of a telephone (i.e., that part ofthe instrument into which one speaks) was termed to be a transmitter, adistinction that continues today. The British inventor David Hughes usedthe word microphone to describe his discovery of a carbon buttontransmitter using a multiple loose contact.

Hughes’ introduction earned him the wrath of Thomas Edison, who laid claimto the invention of the double-button transmitter. Edison maintained thathe had laid claim to the invention some two months prior to Hughes’announcement. Accusing Hughes of piracy, Edison brought to bear all theblame that he could place on his opponents.

Refinements and improvements to the carbon button telephone transmittercame quickly in the years from 1878 to 1882. In testimony to these earlierdevelopers, the carbon-button transducer, the essential element in millionsof telephones in service around the globe, remains basically unchanged.

As their predecessors had focused their attention on improvements to thetelegraph, experimenters of the era were predisposed to seek more reliableand 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 possiblesolutions to better electroacoustic transducers. The problem with all ofthese systems was their inability to amplify the minute output of thetransmitters into a signal that could be deployed over increasing distances.

Acoustical recordingIn the realm of audio, if we may use that term to differentiate soundsystems from their speech transmission brethren, the industry continued inan acoustic-mechanical mode. The carbon button mic, while adequate forspeech transmission, was not adaptable for use in musical recordings.Hence, we might consider that the acoustical horns employed to record andplay back phonograph records were the next version of the mic.

Audio amplificationTo address the next stage in development, we must again visit the telephoneindustry and Bell Telephone’s research arm-the Western Electric Company. By1911, long-distance telephone service had been established between New Yorkand Denver. However, given the available technology, that was the farthestattainable distance of telephone transmission.

Frantic efforts were being made to establish transcontinental telephoneservice as a central exhibit of the 1915 Pacific-Panama Exposition to beheld in San Francisco. Bell Telephone had acquired the rights to Lee deForest’s audion three-element vacuum tube in 1912; however, work continuedon the development of an acoustic-mechanical microphonic repeater. Therewere some doubts as to whether the vacuum tube amp could be perfected toprovide reliable service as a telephone circuit repeater. Service for thetranscontinental system was established in time to meet the 1915 SanFrancisco deadline, but it employed paralleled microphonic and vacuum tubeamps to augment each other in the event of failure. Thus, 1915 saw the dawnof electronic amplification.

New horizons for audioWestern Electric recognized that the vacuum tube amp opened new areas ofapplication. Loudspeaking telephones, what we now know as loudspeakers,made PA systems commercially viable. Experiments in this area wereconducted in field tests before they were suspended for the duration ofWorld War I.

Central to these developments was the work of Edward Wente, who had joinedthe staff of Western Electric in 1914. Using a principle that had been alaboratory curiosity for 50 years, Wente transformed the electrostatictransmitter into the first flat-frequency response mic. Wente called hisinvention a condenser transmitter. So, the condenser mic, still consideredup-to-date technology, was actually introduced in 1916.

Wente continued to perfect the condenser mic until, by 1922, he hadproduced a device with 100 times the sensitivity of his 1916 model, makingthe condenser mic a commercially practical device.

After hostilities in Europe ceased, interest in the development of PAsystems intensified. Both Western Electric and the Magnavox Company ofOakland, CA, vied for installations. When President Warren G. Hardingdedicated the Tomb of the Unknown Soldier on November 11, 1921, thousandsgathered at Arlington National Cemetery to hear his address over a WesternElectric supplied PA system, while thousands more heard his speechtransmitted over telephone lines to audiences at Madison Square Garden inNew 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 avidlisteners; Warner Bothers, in concert with Western Electric, had introduceda workable synchronized film/audio playback system; large audiences instadiums and auditoriums could be addressed with PA systems; and discrecording companies had finally been persuaded to adopt electronicamplification.

Mic improvementAll of these developments necessitated the development of more reliable,improved mics with better fidelity. Concepts were advanced that providedmore directional control of the mic’s pickup pattern and improved theinstrument’s sensitivity.

Western Electric, through its wholly owned subsidiary ERPI (ElectricalResearch Products Inc.), had established a strong relationship with WarnerBrothers Studios, and by virtue of cross-licensing agreements, had amajority position in the motion picture studios and theatres across America.

Condenser mics of that era, while commercially successful (having beentamed by the introduction of directional patterns), still exhibited someserious drawbacks. The high-impedance output of the capacitor elementnecessitated 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 powersupply was required to provide working voltages for the vacuum tubes. Tocircumvent some of these difficulties, Western Electric introduced thefirst high-quality moving-coil (dynamic) mic in the late ’20s.

Others, notably C.B Sawyer and C.H Tower, perfected the crystalelectromechanical 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 ofthis technology. Sawyer and Tower solved the dual problems of growingsufficient quantities of Rochelle salt and ensuring that the salt was pureenough to be practical in the manufacture of mics. Crystal mics were usedbriefly in some of the motion picture studios, but the incompatibility ofRochelle salt and high temperatures made their use in the intense lights ofa studio impractical.

Piezoelectric transducers, however, went on to become useful devices inphonograph pickups, telephone receivers and the production of commercialgrade mics for the communications industry.

Ribbon MicsMeanwhile in Germany, between 1923 and 1926, Schottky and Gerlach ofSiemens developed and patented a method whereby a single metallic ribboncould be substituted for the multi-turn voice coils in loudspeakers. Thedevelopment produced a mildly successful loudspeaker, but more importantly,it stirred the interest of Harry F. Olson at RCA. Olson saw the developmentfor 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 and1941. They exhibited extremely good frequency response, outstandingsensitivity and had the notable advantage of having a bidirectional pickuppattern. The downside was that they were extremely fragile and could onlybe used in very controlled environments.

Ribbon mics enjoyed great popularity in the broadcast and recording fieldfor many years. In addition to RCA, ribbons were manufactured by ShureBothers and some European producers, notably beyerdyamic.

Directivity controlThe next notable development in mics was the marriage of the ribbon elementand the moving-coil element into a hybrid mic. By varying the ratio of theribbon to the moving coil pickup, a unidirectional pattern having thefamiliar cardioid shape was realized. The RCA 77B, introduced in 1937 andfollowed by the Western Electric 639A in 1939, was an example of such ahybrid unidirectional mic.

As sound reinforcement demands increased and multi-mic recordings becamemore prevalent, the need for more directionally controlled mics becameincreasingly evident.

The next evolutionary step was the development of single-elementunidirectional mics. These developments took the form of modifiedmechanical case designs and internal damped pipes to introduce anacoustical delay to sounds arriving off axis to the front of the mic’sdiaphragm-be it a moving-coil or ribbon type. The Shure Brothers UnidyneSeries (Dynamic 1941) and the RCA 77D type (Ribbon 1941) employed theseprincipals.

Neumann, the German mic manufacturer, employed a controlled phase shiftprincipal in the development of its popular unidirectional M49electrostatic (condenser) mic. These principles were developed in the ’30sbut, owing to World War II, did not reach commercial introduction until1953.

During the war, commercial development of mics on both sides of theAtlantic was temporarily suspended, though there were still somesignificant developments in electroacoustic transducers. The crystal(piezoelectric) transducers that had been developed by the British andFrench in 1917 for the purpose of locating such underwater objects as enemysubmarines became the highly successful SONAR systems used during the 1939to 1946 conflict. By 1950, the underlying principles of mic technology thatwe 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 theirsize to make them more readily adaptable to handheld use. The mic casesbegan to take on a cylindrical shape, wherein the element was housed at oneend of the cylinder. In 1954, Electro-Voice introduced this type ofpackaging in the Variable D series. Also in 1954, RCA started delivering aunidirectional ribbon version employing a similar packaging concept.

Altec-Lansing, who had previously seemed content to market the earlierWestern Electric designed dynamic mics, took a serious interest in bringingto market a quality, small-sized condenser product. This resulted in a miccapsule measuring 1.6 cm in diameter and 1.0 cm in depth. The firstcommercial application of this new condenser capsule was in the Altec M11System, which was publicized for its performance and its unobtrusive design.

Altec continued to exploit the small size of its M21 capsule and followedup with its Lipstick series, in which the entire mic (sans cable and powersupply) measured only 3 inches (7.6 cm).

John Hilliard, chief engineer for Altec-Lansing, explained how the namecame 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 makean experimental model, and by comparison the size is practically the same.”

Altec also used this capsule in a number of systems aimed at medicalnoise-control measurements and other nonentertainment audio applications.

Other mic manufacturers did exist in the United States; however, none ofthem were able either to achieve great stature or to penetrate into thestudio market. American Microphone Company made a reasonably good dynamicbut was absorbed by Electro-Voice in the mid ’50s.

More advancementsContinuing the trend toward further miniaturization, Electro-Voice madegreat strides in bringing forth lavalier type products during the ’50s.These were wired devices, but they provided performers and other soundsystem users with a freedom of movement that hitherto had been impossible.

A short-lived product development was the acoustical line array or shotgunmic, in which a unidirectional (dynamic) was coupled to an acoustical tubeot rubes. These were used primarily in TV studios to extend the workingrange of the mic. They suffered from a rather poor frequency response andhad a marginal directivity factor.

Accompanying the drive to reduce the size and weight of mics was a steadyimprovement in the materials and production processes. None of thesedevelopments was as sensational as some of the earlier breakthroughs, butbetter and more reliable products continued to appear. By 1960, polyesterfilms started to replace metal alloy diaphragms in dynamic mics.

Wireless or radio-frequency (RF) mics started making an appearance in theearly 1960s. These devices were not as much a refinement in mic technologyas they were an improvement in transmission technology. The mic capsuleswere essentially the same capsules being used in conventional mics. Theaudio cable had been replaced by an RF link, allowing the user to havevirtually unlimited mobility.

Unfortunately, many of the earlier models operated on the 36 MHz to 50 MHzband, which subjected them to a wide range of interference. They did notemploy any form of limiting, and consequently could be easilyovermod-ulated, causing distortion in the sound system. The vacuum tubereceivers employed were characteristically unstable and subject tofrequency drift. It would be a full two decades before the bugs could besufficiently worked out of the RF transmission system, allowing performersand sound practitioners to rely on the wireless mic.

The development of the FET (field effect transistor) allowed for thepractical construction of the electret condenser mic. Electret technology,wherein the external DC bias required for a convention condenser mic iseliminated, stems from an idea advanced 50 years earlier. By using apermanently polarized dielectric material, the device can be madeself-contained using a readily available electrolyte battery to operate theFET. Electret technology had to wait 50 years until the materials toimplement 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 technologyas it was a truly innovative packaging design. To eliminate unwantedreflective signals from adjacent boundaries, the PZM has its capsulemounted in a manner that essentially prohibits the entry of sound pressurefrom 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 theexclusion of its many varied applications.

I would, however, ask you to bear in mind that, as you place thatstate-of-the-art condenser mic on the stage, you are using a technologythat Dr. Wente first brought to light in 1916.

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