Growth, Mechanism and Uses of Button Microphones

By: Victor Epand

A button microphone is also known as carbon microphone or carbon transmitter. The design of a carbon microphone is quite a simple one. It consists of two metal plates separated by small pieces of carbon. One of the pieces between the two faces outwards. Its function is to work like a diaphragm.

The mechanism by which a button mic works is quite complex. The sound wave, which is caused by the displacement of the air particles, strikes the plate, which acts like a diaphragm. The original pressure that was there in the mic is changed, which results in changing of the electrical resistance between the plates. Difference in the wave pressure changes the speed of the plate movement. The step comes next is the passing of direct current from one plate to another. The change in current can then be used to pass, though an electric system transforming it into a signal.

Advantages and disadvantages of a Button Microphone

One of the basic advantages of a carbon microphone was that it has high output level, as the impedance or the obstacle amount is low. The high level audio signal output comes from very low DC voltages; and as it is itself an amplifier so there is no need for any external amplifiers or batteries.

Various areas, where physical engagement is high, the use of carbon microphones is growing. For example, in opera theatre, where the singers are busy with movements, there they use carbon microphones for smooth flexibility along with easy grasp of the music. In more modern disco clubs, DJs most of the time use button microphones for creating musical blenders.

But the carbon microphones were discarded by the radio broadcasting system after the 1920s due to their low quality sound output, which more often than not had high noise or hiss level. Also, the frequency response for the carbon mic was limited.

History of Button Microphone

The year 1978 saw T. A. Edison and Emile Berliner both claiming for the invention of the carbon transmitter. The two sides had a tough battle over the patent rights; which was later sorted by a Federal court giving Edison the right over the invention.

Other Various Uses of Carbon Microphone

Use of Carbon Microphone as an Amplifier
Surprisingly carbon microphones can also be used as an amplifier. In earlier telephone repeaters this attribute was put into use. In this arrangement, a telephone receiver was mechanically coupled with a carbon mic to boost weak signals and send them down the telephone line. In the 1930s it was also used in some audio equipments, especially in hearing aids. In the 1950s, however, the transistors replaced their earlier counterparts.

Early Amplitude Modulation or AM based radio also depended on the carbon mic for voice modulation of the radio signal.

Modern day use of the Button Microphone
In some developing countries the legacy telephone installations still uses them to a greater extent. Some third world countries use them in some niche applications. One such example is the Shure 104c, which is quite compatible with some of the existing equipments.

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