![]() ![]() This preamp is frequently phantom powered in sound reinforcement and studio applications. 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). It is equivalent to the back electret in that any conductive film may be used for the diaphragm. The electret film is adhered to the inside front cover and the metalized diaphragm is connected to the input of the FET. Front electret This design features no back plate, and the capacitor is formed by the diaphragm and the inside surface of the capsule. 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. Modern materials have enabled very comparable performance to other designs. It is often considered the lowest quality, as the electret material used sometimes does not make a particularly good diaphragm. There are three major types of electret microphones, differing in the way the electret material is used:įoil-type or diaphragm-type A film of electret material is used as the diaphragm itself. This became the most common type, used in many applications from high-quality recording and lavalier use to built-in microphones in small sound recording devices and telephones. Modern electret microphones use PTFE plastic, either in film or solute form, to form the electret.Įlectret materials have been known since the 1920s and were proposed as condenser microphone elements several times, but they were considered impractical until the foil electret type was invented at Bell Laboratories in 1961 by Gerhard Sessler and James West, using a thin metallized Teflon foil. ![]() The polar molecules of the dielectric align themselves to the direction of the electrostatic field, producing a permanent electrostatic "bias". ![]() Electrets are commonly made by first melting a suitable dielectric material such as a plastic or wax that contains polar molecules, and then allowing it to re-solidify in a powerful electrostatic field. The name comes from electrostatic and magn et drawing analogy to the formation of a magnet by alignment of magnetic domains in a piece of iron. The audio signal appears at the output, after a DC-blocking capacitor.Īn electret microphone is a type of electrostatic capacitor-based microphone, which eliminates the need for a polarizing power supply by using a permanently charged material.Īn electret is a stable dielectric material with a permanently embedded static electric dipole moment (which, due to the high resistance and chemical stability of the material, will not decay for hundreds of years). The resistor sets the gain and output impedance. The two-terminal electret capsule contains an FET which must be externally powered by supply voltage V +. JSTOR ( September 2012) ( Learn how and when to remove this template message)Įlectret condenser microphone capsules A typical electret microphone preamp circuit uses an FET in a common source configuration.Unsourced material may be challenged and removed.įind sources: "Electret microphone" – news Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification. ![]()
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