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It is equivalent to the back electret in that any conductive film may be used for the diaphragm. Electret microphones require no polarizing voltage unlike other condenser microphones , but normally contain an integrated preamplifier which requires a small amount of power (often incorrectly called polarizing power or bias).
English: A typical electret microphone preamp circuit uses a FET in a common source configuration. The two-terminal electret capsule contains an FET which must be externally powered by supply voltage V +. The resistor sets the gain and output impedance. The audio signal appears at the output, after a DC-blocking capacitor.
Electret microphone elements typically include a junction field-effect transistor as an impedance converter to drive other electronics within a few meters of the microphone. The operating current of this JFET is typically 0.1 to 0.5 mA and is often referred to as bias, which is different from the phantom power interface which supplies 48 volts ...
In order to take a scientific measurement with a microphone, its precise sensitivity must be known (in volts per pascal). Since this may change over the lifetime of the device, it is necessary to regularly calibrate measurement microphones. This service is offered by some microphone manufacturers and by independent testing laboratories.
A microphone or other device can obtain DC power from either signal line to ground terminal, and two capacitors block this DC from appearing at the output. R1 and R2 should be 6.81k ohms for "P48" 48-volt phantom. R3–6 and Zener diodes 1–4 deliberately clip the outputs to ±10v to protect a subsequent circuit from potentially large transients.
First patent on foil electret microphone by G. M. Sessler et al. (pages 1 to 3) An electret microphone is a type of condenser microphone invented by Gerhard Sessler and Jim West at Bell laboratories in 1962. [24] The externally applied charge used for a conventional condenser microphone is replaced by a permanent charge in an electret material.
Gerhard M. Sessler (born 15 February 1931 in Rosenfeld, Baden-Württemberg, Germany) [1] is a German inventor and scientist. He is Professor emeritus at the Department of Electrical Engineering and Information Technology of the Technische Universität Darmstadt.
An electret (formed as a portmanteau of electr-from "electricity" and -et from "magnet") is a dielectric material that has a quasi-permanent electrical polarisation. An electret has internal and external electric fields , and is the electrostatic equivalent of a permanent magnet .