What Are Carbon Microphones Used For?

In audio production we utilize many different kinds of microphones that can carry out specific tasks. For example condensers capture vocals, dynamic mics capture louder sound such as sound effects and instruments.

A carbon microphone is not a common microphone and in this post I’m going to walk you through its uses.

“What is a carbon microphone” is a common question I usually run into from most newbie audio guys.

Therefore, I’m going to provide my expertise and give you all the necessary insight that you need on carbon microphones.

With that said, lets dive into this post…….


What are carbon microphones used for?

Carbon microphones are a very old kind of microphone that were mostly used for public address, broadcast, military operations, and telephony.

An Overview of carbon microphones

The carbon microphone, is also known as a carbon button microphone, button microphone, or carbon transmitter. It is a type of microphone, with a transducer that is able to convert sound to an electrical audio signal.

The transducer is made up of two metal plates that separated by granules of carbon.

One of these plates is very thin and faces toward the speaking person and therefore acts as a diaphragm. 

Sound waves striking the diaphragm cause it to vibrate thereby exerting a varying pressure on the granules, which in turn changes the electrical resistance between the plates.

Higher pressure lowers the resistance as the granules are pushed closer together.

A steady direct current is passed between the plates through the granules.

As a result, the varying resistance results in a modulation of the current, creating a varying electric current that reproduces the varying pressure of the sound wave.

In telephony, this undulating or fluctuating current is directly passed through the telephone wires to the central office.

In public address systems it is amplified by an audio amplifier that offers the needed boost.

 The frequency response of most carbon microphones, however, are limited to a very narrow range, and the device notably produces significant electrical noise.

Applications explained

Carbon microphones were an ideal choice of microphone in the early days of the telephone.

They were widely used in telephone applications because they had the ability to provide a high output which meant that no amplification was needed.

As radio began to take off as a way of broadcast, the carbon microphone was initially used there for broadcasting as well as for communications purposes.

However their use in broadcast applications soon came to end because of the drawbacks of the noise and poor frequency response.

Other types of microphone started to become available and their use was preferred because of the better fidelity they were able to offer.

For a couple of years, the use of the carbon microphone persisted for communications purposes as they gave a high output an were robust.

The poor frequency response was not really looked at as an issue.

The carbon microphone was used for telephones up until the 1970s and 1980s, but even there it became possible to use other types of microphone more conveniently.

Also the crackle and noise of the carbon microphone had always been an issue and when other types of microphone became available at a low cost they started to be used, despite the requirement for additional electronics needed.

Carbon microphone advantages & disadvantages

As with any form of microphone there are advantages and disadvantages.

Carbon microphone advantages

High output

Carbon microphones were the go to mics because of their high output and this is one advantage they have.

Simple principle & construction

Carbon microphones relied on a simple mechanism for operation and thus were easy to build without the need for outsourcing components.

This made them relatively easy to work with.

Therefore the major advantage when broken down is that they were relatively cheap and simple to manufacture.

Carbon microphone disadvantages

Very noisy

High background noise and on occasions it would crackle. This is one of the reasons why radio as industry started to use other alternative microphones for broadcast.

Poor frequency response

Carbon microphones have a poor frequency response which means they can only be used for certain specific purposes.

Requires battery or other supply for operation

Carbon microphones need batteries or a supply of power for operation. Without this supply, they’re unusable.

Final Thoughts

The carbon microphone has a number of advantages, but today the disadvantages normally outweigh the positives and as a result they are rarely used..