Electret Condenser Microphone

We are going to begin this material by defining the electret condenser microphone (ECM).

This device consists of a very light diaphragm and of a back plate, which is attached with a polarizing voltage. Its principle of operation is that the sound waves impinge on the diaphragm and, thus, they cause the capacitance between it and the back plate to change in sympathy.

After this process a s.c. voltage is induced on the back plate. The electret condenser microphone has a permanent charge voltage, which is implanted in the electret material so that it provides the polarizing voltage. This process can be effected in three ways. Usually, the electret material is represented by the diaphragm, which is metalized on one side. This is not the best choice of diaphragm material, thus, when higher performance is

electret condenser microphone - Sony ECM77B

needed the electret material is applied on the back plate, the diaphragm being made of a different material. This type of electret condenser microphone is also known as the "back type".

However, there is a more recent variation of this process, which is called the "front type". In this case, the electret material is attached to the inside of the front cover of the microphone. The metallic diaphragm is, in its turn, connected to the input of the FET. The whole process is based on the variation in capacitance between the front cover and the diaphragm, variation, which is produced by the sound waves that impinge on the diaphragm.

The advantage of the electret microphone is that it is immune to vibration because of the very light weight of the diaphragm. This is very useful in the telecommunication field and also when it is used as incorporated in moving items such as motors in dictation machines and cassette recorders.

Electret Microphones

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