Carbon microphone

The carbon microphone is a special kind of microphone that changes sound into an electrical audio signal. It has two metal plates with granules of carbon in between them. When sound waves hit the thin plate, which acts like a diaphragm, it moves and puts different amounts of pressure on the carbon granules. This changes the electrical resistance between the plates.

A steady electric current flows through the plates, and the changing resistance makes the current change too, just like the sound waves. In old telephone systems, this changing current would travel through the wires to reach someone else. In other systems, it would be made louder by an audio amplifier.

Carbon microphones were very important before electronic amplifiers became common. They were used in telephones for many years because they were cheap and worked well for basic voice calls. They were also used in early AM radio broadcasting and some radio systems, but they had limits and made some noise, so they were replaced by better technologies later.

History

The first device that could carry voice calls was a carbon microphone. It was made around 1878 by David Edward Hughes in England and also by Emile Berliner and Thomas Edison in the US. Hughes showed his working device to many people years before Edison got a patent. His device used small carbon pieces that changed how much they resisted electricity when squeezed by sound waves. This made it possible to turn sound into an electrical signal that could carry voice.

Carbon microphones were very important for the start of telephones, radio, and recording. They were used in phones from 1890 until the 1980s. These microphones worked by changing the electricity flow when the sound waves moved parts inside them.

Use as amplifier

Carbon microphones could also help make sounds louder. They were used in early phone systems to make long-distance calls possible before better technology came along. These early loudness helpers used a phone part connected to a carbon microphone to boost weak signals. They were replaced by newer technology but were still used in small portable devices like hearing aids for a while.

Early radio applications

The first radio voice broadcasts used carbon microphones to change voice into radio signals. Early long-distance audio transmissions in 1906 used a special carbon microphone to send voice signals through radio waves.

Current usage

Carbon microphones are still used in some special places even though many makers have stopped selling them. One example is the Shure 104c, which was popular in the late 2010s because it works well with older equipment.

A big benefit of carbon microphones is that they can create strong audio signals from very low electricity, without needing extra power from batteries. This makes them useful in faraway places with long telephone wires, where the electricity can be very weak. Most modern telephones need at least three volts to work, but carbon microphones can still work with just a tiny bit of electricity. They also do not have a problem where one telephone stops all others from working on the same line.

Carbon microphones are also used in important places like mining and chemical factories where higher electricity could cause sparks and explosions. They are also strong enough to survive damage from lightning or strong bursts of energy, making them good backup systems in military places.