Microphones are transducers. Electret Condenser Microphones (ECMs) have both moving and stationary parts. Each part of an Electret Condenser Microphone (ECM) plays a significant role.
Simply put microphones are transducers. As a transducer a microphone converts acoustic energy into electric energy. This is quite the opposite of a loudspeaker driver which converts electric energy into acoustic energy. In an electret condenser microphone the energy conversion – acoustic to electric- is done when the distance between the two plates of the capacitor is varied. More about the principle of operation of an ECM in the next blog.
The electret condenser microphone consists of both moving and stationary parts and each part, though very small, has a significant role to play in the operation of the microphone.
Microphone Case: Made from a metal alloy, typically an Aluminum alloy, for its light weight, strength and durability. It is what houses all the parts that make up the electret condenser microphone.
Diaphragm: Like a speaker driver, an electret condenser microphone also has a diaphragm. The diaphragm is the only moving part of the electret condenser microphone and acts as the variable plate of a capacitor. The other plate of the capacitor being formed by the back plate to which we turn next.
Back plate: The back plate forms the other plate of the capacitor and it is stationary.
Spacer: As you can see from the exploded view of the ECM the spacer sits between the back plate and the diaphragm. It is made from plastic and though very small it has the big job of keeping the back plate and the diaphragm (the two plates of the capacitor) from touching each other, thus preventing short circuits.
Plastic cavity: Since the back plate is permanently charged and the case is made from an Aluminum alloy we need to insulate the back plate from the metal case. The plastic cavity is “charged” with the responsibility of insulating the back plate from the metal case.
Copper ring: The small copper ring connects the back plate to the PCB thereby transmitting the variable voltage produced by the diaphragm and back plate to the FET for amplification.
Additional information on Electret Condenser Microphones can be found:
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