October 2, 2023


Digitally first class

History, Growth And Development Of Modern Microphones

The word microphone comes from the Greek words micro meaning small, and phone meaning voice. It first appeared in a dictionary in 1683 as an instrument by which small sounds are intensified.

This was in reference to the acoustical hearing devices such as the ear trumpets and megaphones of that era. Microphones were introduced with the first articulated telephone transmitters, developed almost simultaneously by Elisha Gray and Alexander Graham Bell. Then it was used as a liquid transmitter, which was a variable resistance device. But the poor quality of these liquid transmitters prompted a number of inventors to pursue alternative avenues of design.

Entered the telephone business late in 1877. Now with two companies trying to develop a better transmitter, other experimenters began to appear and offer their devices. David Edward Hughes was one such man who designed a new kind of microphone, using carbon granules loosely packed in an enclosed space.In response to the varying pressure from a sound diaphragm, the electrical resistance through the carbon granules changed proportionally.

Another notable scientist Thomas Alva Edison refined the carbon granule microphone, resulting in the carbon button transmitter in 1886. Edison transmitter was simple and cheap to manufacture, but also very efficient and durable. It has become the basis for the telephone transmitters used in millions of telephones around the world.

The next important step in transmitter design was by Henry Hunnings of England. He used granules of coke between the diaphragm and a metal back plate. This design originated in 1878 and was patented in 1879. This transmitter was very efficient and could carry more current than its competitors. Its one drawback was that it had a tendency to pack and lose its sensitivity.

The advent of electrical disc recording and radio broadcasting in the early 1920s stimulated the development of better quality carbon microphones. The year 1920 ushered in the commercial broadcast era. Some of the knowledgeable amateurs and singers started playing records and using microphones with their programs. The early radio station used the candlestick telephone for a microphone.

The typical transmitter element at this time was the Western Electric No 323. At first it was used as talking into it as one would use a telephone. The next step was to provide the entertainers with a microphone that would allow them to stand and perform. For this application the constructor took the transmitter of the candlestick telephone, replaced the short mouthpiece with the megaphone and slid this combination into a felt lined Bakelite sleeve about eight inches long and put small eyebolts on each end to suspend it from above.

The first microphone, which made for the movie industry was the PB17. It was a sandblasted aluminum cylinder, 17 inches long and 6 inches diameter .The bottom was rounded with a yoke to hold the ribbon element, which had a protective perforated screen. The magnetic structure used an electromagnet requiring six volt at one ampere.

In recent years, some of the more radical approaches to microphone model design have included detecting the movement, in response to sound pressure variations, of charged particles, a system analogous to the ionic loudspeaker. Miniature optical interfaces and related devices developed for the telecommunications industries, such as miniature laser diodes, polarizing beam splitters and photodiodes, are now helping in the construction of the high quality optical microphones.