Types
There are three major types of electret microphone, differing in the way the electret material is used:
- Foil-type or diaphragm-type
- A film of electret material is used as the diaphragm itself. This is the most common type, but also the lowest quality, since the electret material does not make a particularly good diaphragm.
- Back electret
- An electret film is applied to the back plate of the microphone capsule and the diaphragm is made of an uncharged material which may be mechanically more suitable for the transducer design being realized.
- Front electret
- In this newer type, the back plate is eliminated from the design, and the condenser is formed by the diaphragm and the inside surface of the capsule. The electret film is adhered to the inside front cover and the metalized diaphragm is connected to the input of the FET. It is equivalent to the back electret in that any conductive film may be used for the diaphragm.
Unlike other condenser microphones electret types require no polarizing voltage, but they normally contain an integrated preamplifier which does require a small amount of power (often incorrectly called polarizing power or bias). This preamp is frequently phantom powered in sound reinforcement and studio applications. Other types simply include a 1.5V battery in the microphone housing, which is often left permanently connected as the current drain is usually very small.
Read more about this topic: Electret Microphone
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