Three Common Types Of Aviation Microphones

There are three common types of aviation microphone in use. These are:

Carbon Microphone
Dynamic Microphone
Electret Microphone

All these microphones have one common factor and that is they all change sound waves into a fluctuating electric current that can be transmitted, using the vibration of the diaphragm to cause the fluctuation in the electric current. How this vibration is converted into the electric current is the basic difference in the microphones.

Carbon Microphone: The least expensive and the simplest in design. Basically, the sound is transformed into electrical signals by sound waves striking a diaphragm, causing the diaphragm to vibrate. A small vessel containing carbon granules is attached to the diaphragm and as the diaphragm vibrates the carbon granules move. The small electrical current, that is flowing through the system, fluctuates due to the movement of the carbon. This fluctuation in the current is then amplified and transmitted.

Dynamic Microphones: This method, in terms of price falls somewhere in the middle of the range. In this type of microphone, the diaphragm has a coil of wire attached to it, which has a strong magnetic field. The vibration of the diaphragm and electric coil cause an electric signal that fluctuates in voltage in response to the frequency and amplitude of the diaphragm’s vibration.

Note: The magnetic field used in Dynamic Microphones are susceptible to electromagnetic interference. This can easily damage the signal, and so this type of microphone utilises some sort of electric shielding, to cancel or at least minimise this interference.

Electret Microphone: This type of microphone is both smaller and lighter than the other types and is the one most extensively used. A charged diaphragm is placed a given distance away from a fixed plate. The vibration of the diaphragm caused by sound waves change the distance between the diaphragm and plate. This is what causes the fluctuation in the electrical signal and is then amplified and transmitted.

Noise Cancelling: This is achieved in all microphone types by allowing the ambient noise to reach both sides of the diaphragm and thus effectively cancelling each other out and the diaphragm doesn’t move. This then leaves the sound waves caused by speach to act on one side of the diaphragm only, which causes the vibration required to cause the electric signal.

Whereas this is the same basic method used by all microphone types to achieve noise cancelling, it is recognised that Electret Microphones achieve a greater effect.