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What is an Electret Microphone?

written by: Kristina Dems•edited by: Amy Carson•updated: 4/18/2011

An electret microphone is a device that uses two conducting plates to capture sound waves and translate them into electrical waves. This simple design is found in other types of capacitor microphones, except here less power is needed thanks to a conducting plate with an attached insulator.

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    Electret Microphone

    Electret Microphone An electret microphone is an omnidirectional microphone, which means it can capture sound from all directions. It is one of the most widely used types of microphones in any field where a microphone is needed. Its good performance and inexpensive quality makes it very popular all around the world for different uses. What sets it apart from types of microphones is how it transmits sounds to output devices.

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    The Design of Electret Microphones

    It uses two conducting plates; one is fixed while the other is a vibrating diaphragm. This kind of design is found in all capacitor microphones, which are types of microphones that deliver great sound quality but requires a constant source of electrical charge to produce electrical signals that communicates the sounds made by the diaphragm into sound that comes out of outputs devices likes speakers. What makes it different from generic capacitor microphones is that it does not need a constant source of electrical charge. Its diaphragm is actually made of insulating material that contains a permanent electrical charge. This makes it very efficient by producing quality sounds without requiring a constant source of electrical charge.

    This kind of design usually makes the diaphragms heavier because of the insulating material, but newer electret microphone designs feature a more efficient design wherein the insulating material is attached to the stationary back plate and not to the diaphragm, making it lighter and thinner, providing a more energy efficient microphone that produces roughly the same sound quality as capacitor microphones.

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    How Electret Microphones Work

    With the diaphragm and the back plate ready to receive sound waves, they work by letting the incoming sound waves from a source of sound from any direction to change the capacitance between the two conducting plates. The diaphragm is the conducting plate that receives the sound waves and it causes the change in capacitance. This change in capacitance produces variance in voltage on the back plate and this, in turn, sends electrical signals to output devices like speakers and sound systems. It may seem magical and mind-blowing, but this technology has been around for decades. Its simplicity lets it stand the test of time and even with some modifications through the years, the basic principle of using two conducting plates to deliver electrical signals that represent sound waves is still there.

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    The Different Uses of Electret Microphones

    Due to its simple and low cost design that produces great sound quality through output devices, the electret microphone has earned the trust of people all over the world no matter what their purpose for using a microphone is. Since it is an omnidirectional microphone, it can be used for recording sessions for both voice and instrumentals. It can also be used in live performances and like stand-up comedy or band performances. Broadcasting through television and radio are also fields where this kind of microphone is very popular. Karaoke bars, classrooms and all type of places where a microphone is needed to amplify and broadcast voices or other kinds of sounds are usually using this type of microphone.

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    References

    http://www.soundonsound.com/sos/1995_articles/jun95/microphones.html

    http://www.jlworld.com/website/Technology?OpenForm&CP=MIC

    http://www.epanorama.net/circuits/microphone_powering.html

    Photo Courtesy of EiTrade.com