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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.
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An electret microphone is a microphone whose diaphragm forms a capacitor (historically-termed a condenser) that incorporates an electret. The electret's permanent electric dipole provides a constant charge Q on the capacitor.
The condenser microphone, invented at Western Electric in 1916 by E. C. Wente, [22] is also called a capacitor microphone or electrostatic microphone—capacitors were historically called condensers. The diaphragm acts as one plate of a capacitor, and audio vibrations produce changes in the distance between the plates.
Two examples of different boundary mics (top) and a diagram of the elements of a boundary microphone. The diagram shows the location of the mic capsule, the plate, the aperture, and the pressure zone. In 1978, audio engineers Ed Long and Ron Wickersham studied the effects of the boundary layer in sound recording.
Some condenser microphones can be powered with a 1.5-volt cell contained in a small compartment in the microphone or in an external housing. Phantom power is sometimes used by workers in avionics to describe the DC bias voltage used to power aviation microphones, which use a lower voltage than professional audio microphones.
The U47 was the first condenser microphone switchable between cardioid and omni-directional pick-up patterns. It incorporated the highly successful 12- micron -thick M7 capsule and VF-14 tube amplifier, which was a metal-clad pre-World War II pentode changed to work as a triode .
Condenser microphones have impedance converter (current amplifier) circuitry that requires powering; in addition, the capsule of any non-electret, non-RF condenser microphone requires a polarizing voltage to be applied. Since the mid- to late 1960s most balanced, professional condenser microphones for recording and broadcast have used phantom ...