What is an Electret Microphone?

Electret Microphones

An Electret microphone is a type of condenser microphone that comes with a permanent charge built into it. All microphones need a pair of charged plates (positive and negative plates) in order to function and record sound. General condenser microphones do not come precharged but need an external voltage to charge the microphone's diaphragm for the microphone to operate. Electret microphones, however, come with a permanent built-in charge.

An electret microphone is a variation of the condenser microphone. Instead of requiring an external voltage source to charge the diaphragm, an electret microphone uses a permanently charged plastic element (electret) placed in parallel with a conductive metal backplate.

Even though electret microphones come precharged and do not need voltage to charge them up, they do still require voltage to operate. The voltage doesn't charge the diaphragm like condenser microphones, but voltage is needed to power the amplifier, which most electret microphones come built with. Most electret microphones have a small FET amplifier built into their cases. This amplifier requires power to operate- typically a voltage between +4 and +10 V is needed. This voltage is fed into the microphone through a resistor (1KΩ to 10KΩ). See the diagram below to see the setup.

Powering an Electret Microphone

Electret microphones respond best to frequencies within the lower-middle to high-frequency range- they do not respond well to bass frequencies. For this reason, they tend to be restriced to voice communications.

One disadvantage of electret microphones is that its performance decreases over the years; as time passes, the charge on the electret is lost.

Related Resources

What is a Condenser Microphone?

What is a Dynamic Microphone?

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