A type of microphone design, similar to condenser. Basically, there is a permanently charged plate in the mic element. As the diaphragm moves in response to sound pressure, it creates a changing capacitance with the plate. The big advantage to using electret (also called back-electret, or occasionally prepolarized condenser) technology is that it does not require an external polarizing voltage (battery or phantom power). In some cases, the microphone includes an impedance changing preamp that requires battery or phantom power, but the electret element itself does not require voltage. Electret mics can lose their charge in high humidity and high temperature environments, so some care should be used in storing and using them. If the electret loses charge, the mic’s sensitivity will suffer, resulting in an reduced signal to noise ratio.