Mikrofonní a sluchátková vložka

Year of manufacture: 1920s - 1990s

Another key component of the classic telephone is the microphone and the earphone. The microphone is of carbon type, it is composed of a cavity filled with carbon particles. It was invented in the 1870s. One side of the cavity is made of a thin flexible metal and serves as a membrane. An electric circuit is connected between the membrane and the outer walls of the microphone. The sound waves pressurize the membrane and the carbon particles and the electric resistance of the microphone changes, which creates sound signal in the flowing current. The main advantage of this type of microphone is that it amplifies - the power of the output electric signal is much higher than the power of the sound wave. The output signal is strong enough to be sent over the telephone line without any further electronic amplification. The disadvantages are its high output noise and rumble caused by carbon particles movement when the microphone changes position. The development of miniature electronics in the 1980s enabled its replacement with higher quality microphone types with a separate amplifier.

The earpiece consists of a coil, a permanent magnet and a metal membrane. The coil is wound on the magnet core and the membrane is placed near the poles of the magnet. The alternating current flowing through the coil causes the force between the membrane and the magnet to change and the sound is reproduced.