Carbon Microphones

Carbon microphones are devices with high output levels and low impedance. Plus, they tend to be pretty affordable. Nevertheless, they have a limited frequency response. As dynamic microphones and condenser microphones became more affordable, carbon microphones lost their popularity. Before delving into its features, here’s an interesting fact. Thomas Edison patented the first carbon microphone in 1976. Yet, most of the credit went to Emile Berliner and David Edward Hughes, who also created a carbon microphone around the same time.

Some History on Carbon Microphones

Before vacuum tube amplifiers became popular, carbon microphones were the only devices that could achieve high-level audio signals. They were most common in telephone systems and radio broadcasting (but less so). Firstly, their low cost, high output, and unique frequency response made them the perfect choice for these systems. The old telephone service (POTS) also used them because they did not need modifications. Secondly, in the case of AM radio broadcasting systems, their usage didn’t last long because of their limited frequency response and their high-noise level. Eventually their popularity stopped when someone invented a better and more affordable technology.

Carbon Mics: Characteristics

Physically, a carbon microphone includes a small cup which contains pulverized carbon. A brass disk, known as the botton, encloses this cup. The button adheres to a circular metal diaphragm. When the button and the backplate mix in, they create connection terminals. For its activation, this type of mic uses voltage: it activates due to a battery that runs through the carbon. 

The production of vibration occurs when a sound hits the diaphragm. Then, the carbon granulates and becomes alternately more and less dense as the diaphragm moves. The electrical resistance of the carbon passes through. In doing so, it transforms the battery voltage into a moving current that is an electrical image of the given sound. Afterwards, the transformer stops the current and isolates the low impedance of the device from the input.

Speaking the Truth About these Mics

Carbon microphones are not perfect. Even more so, they are definitely not highly distinguished for their sonic peculiarities. Regardless, they are affordable and resistant, so people use them within sound applications. Their main issue is that they might become inefficient and noisy when the granules at the bottom end are pressed together. However, this problem can be is easily solved by tapping the device against a hard surface.