Microphones…the Acoustic Era

Posted on February 9, 2014 Updated on November 6, 2019

Three cheers for Gorilla Inventors!

Microphone of Caveat April 11, 1877 with mouthpiece added

Berliner blasts the Bell patent pork in 1876:

1. Who was Emile Berliner?  2. What did he do that pissed off Thomas Edison?  3. Who takes credit for the first carbon microphone patent in 1877?

The unveiling of Alexander Graham Bell’s telephone in 1876 inspired Emile Berliner, a young man with rudimentary knowledge of electricity & physics to improve on the telephone’s transmitter.  He invented a “loose contact” metal-to-metal transmitter (type of microphone) to function as a telephone speech transmitter, then wrote and filed the patent himself, causing a stir among the titans of technology.  Thomas Edison followed his lead and filed patent applications for the carbon microphone in June 1877.  After a long legal battle, Edison emerged the victor, and the Berliner patent was ruled invalid by both American and British courts.

Berliner was quickly picked up by Thomas Watson of the American Bell Telephone Company and employed as a researcher until 1884 when he set out with new wife, Cora & his recently acquired American Citizenship to pioneer in Washington DC as an independent Researcher & Inventor.  In 1886, he began working on his greatest contribution to the world: the gramophone…making possible the recording and reproduction of sound using disc records

Ok let’s take a closer look at the “micro” drama:

In 1876 a liquid transmitter (variable -resistance device) was developed by Elisha Gray & Alexander Graham Bell (simultaneously):

Bell’s box telephones (magneto transmitters) worked well as receivers but as transmitters, their signal output was too weak to carry any great distance.  User had to shout into the mouthpiece only to be barely heard on the other end three miles of wire away.  Transmitter design would have to be improved…enter competition from Western Union…Thomas Edison’s lampblock carbon unit, “the Blake” (variable-resistance transmitter) with improvements in sensitivity & reliability courtesy of our favourite rogue, Berlinger, outperformed Bell’s Magneto type until Henry Hunnings came on the scene in 1879 with a new transmitter design using granules of coke between the diaphragm and a metal backplate.  In 1886, Edison improved on Hunnings design by designing a small button-type container and using processed anthracite granules.  In 1892, A.C. White pushed the button  by using a polished carbon block as a rear plate and a similar block in front against a mica disc, with the carbon granules in between.  The mica disc worked like a piston.  Known as the Whit “solid-back” type, it was the industry’s first reliable transmitter and was used from 1892 until about 1925

The telephone transmitter as the only available microphone in 1900, was finding other applications thanks to the invention of wireless telegraphy by Nikola Tesla in 1895.  Gorilla inventors were trying to modulate wireless radio waves so that speech could be sent on them.  As there were no amplifying currents in those days, the microphone was connected into the antenna and had to carry the circuit’s full current.  Only very low-power radio transmitters could accommodate the use of the telephone transmitter whose maximum current capacity was about one-half ampere, leading to the use of multiple microphones with a common mouthpiece.  Rudolph Goldschmidt (a fan of Jersey Shores) introduced a patented circuit for working microphones in parallel to address the problem of failure of the group due to the short circuit of one transmitter.

The hunt for high-power microphones revived earlier patents for condenser transmitters (Edison in 1879 & Dolbear in 1881) and sparked a culture of electronics experimentation & inquiry between 1900 & 1915.  Berliner made a high-current carbon microphone that was air cooled by a fan mounted under the microphone…noisy! Blondell & Chambers developed “flame microphones“ based on spark rods in an oscillating circuit adjusted just short of sparking, using speech vibration to alter the gas supply pressure and vary a flame’s resistance in the gap which would cause sparking to occur.  Liquid or “hydraulic” microphones came upon the scene at this time using the flow of a fine stream of conducting liquid from a reservoir traveling about five feet until the stream would break into droplets.  Sound variations on an elastic diaphragm were driven by a metal diaphragm behind the mouthpiece to carry the pressure of the stream, producing  a variable resistance in proportion to the sound on the diaphragm.  Using 65 volts at 12 amps (780 watts) a one-horsepower microphone was possible (until someone opened a door or sneezed).  The development of heavy-current microphone relays by Fessenden & Dubilier as well as advancement in circuit design by C. Egner & J.G. Holmstrom furthered the cause of high-current microphone technology.  In 1911 the “magnetic modulator” was invented by Alexanderson, a transformer that could handle up to 75 kilowatts for use with an RF alternator.  General Electric picked up on this technology, producing smaller transformers for the 5 to 100 watt transmitters used in Amateur Radio.

World War I created an immediate demand for improved communications and Western Electric, General Electric & The Magnavox Company with the help of vacuum tube technology put the microphone back into a simple circuit leading to the development of  “noise-cancelling” hand held microphones for the military.  These companies introduced various styles of “loudspeakers”  and amplifiers for public address systems including Western Electric’s “Chauphone”  and Magnavox’s “Telemegaphone” which was used to broadcast President Woodrow Wilson’s speech to 50,000 Americans gathered in the San Diego Stadium in 1919.

Radio amateurs found themselves sought after as entertainers thanks to the  “candlestick telephone” (Western Electric transmitter No 323) and in 1920, commercial broadcasting was born. Westinghouse launched several radio stations in 1920 & 1921, picking up the microphone slack with the development of the “dishpan” microphone which permitted mellowing out of the squeaky high-pitched sound of the telephone transmitters with bass and midrange.  Improvements on this design with a condenser element was known as a “tomato can” popularized by General Electric who made most of the microphones sold by RCA between 1919 & 1927 including the “bullet” in 1926.  By 1931, Western Electric (a subsidiary of the American Telephone & Telegraph Company) however, emerged as the leader in microphone engineering waxing Westinghouse & General Electric and despite the explosion of small microphone manufacturers such as Electro-Voice, only RCA survived as a major contender with the introduction of the 44A ribbon velocity bidirectional microphone.

HISTORY OF RECORDED SOUND:

GO DEEPER WITH THESE LINKS:

http://www.charm.rhul.ac.uk/history/p20_4_1.html

http://www.edisontechcenter.org/speakers.html

http://en.wikipedia.org/wiki/Timeline_of_the_telephone

compare with modern microphone technologies:

electromagnetic induction (dynamic mic);  condenser capacitor change (condenser mic); light modulation (mechanical vibration produces a voltage signal)