In 1942 after America entered World War 2, the US military estimated that only 20% of radio communications in combat were successful. Failure in the other 80% was mainly due to the voice of the radio operator being drowned out by the surrounding cacophony of war. Like no other conflict before, success on the battlefield relied on communications. Spotting a gap in the market Al Khan and Ed Burrows, the owners of Electro-Voice, came up with a brilliantly simple, ingenious and cost effective solution to this problem.
Even in 1942 the single button carbon microphone was a piece of old fashioned tried and tested technology, having been in use in telephones since the tail end of the previous century. Although the audio quality of the T45 is little better than it’s telephonic predecessors it is extremely reliable and very robust. It also has a high output making it ideal for long distance communication. Even if the microphone gets wet you can simply dry it out (as per the instructions above) and it will carry on working! However, the really clever part of this design utilises 2 small holes of equal size on the front and back of the mic.
These allow the surrounding noise to enter the microphone on both sides of the diaphragm. The sound striking the back of the diaphragm is 180 degrees out of phase with the sound at the front. This causes a very impressive cancellation of the unwanted noise whilst the speaker’s voice, which is less than a 1/4 of an inch from the front opening, dominates the transmission.
In terms of manufacturing costs it would be hard to produce a cheaper microphone. A carbon button is a very small tin of glorified coal dust (carbon granules) with a simple diaphragm attached. A bit of wire and some lightweight plastic fittings and that is it! Pure genius !
After some initial military skepticism the product was thoroughly tested and a first order came through to Khan and Burrows for 100,000 units! The T45 was soon taken up by all branches of America’s armed forces and the success rate of combat communications rose to 90%.
Rags to Riches.
Prior to World War 2 Electro-Voice was a small struggling company, with 20 employees, manufacturing a handful of dynamic and velocity microphones per week. By the latter part of the war Electro-Voice had 500 employees working in 3 shifts producing more than 2,000 T45 microphones a day! After WW2 it was also adopted by commercial aviation and remained in service for several decades. The T45 was also used on the Mercury, Gemini and Skylab space missions.
Over the entire production run more than a million were produced placing the T45 among the highest selling microphones ever made.
During the war many small firms went out of business due to a shortage of manpower and materials, but for those involved in the war effort fortunes were to be made. In 1946 Electro-Voice moved into an impressive new factory at Buchanan Michigan where they continued to manufacture innovative and exciting audio products for the next 60 years.
Circuit for powering a carbon microphone.