Why do electret condenser microphones usually require an external power supply?

Electret condenser microphones usually require external power supply, mainly due to the characteristics of their working principle and internal structure. Here are a few of the main reasons:

Working principle: The electret condenser microphone contains an electret film inside, and free charges are distributed on this film. When sound waves cause the membrane to vibrate, it changes the distance between the two electrodes, thereby changing the capacity of the capacitor. However, the voltage generated by this change is very weak and requires external circuitry to amplify it for normal use.

Signal amplification: Since the voltage generated during the conversion of sound into electrical signals is very small, it is not enough to directly drive external devices. Therefore, a power supply is needed to provide enough current to drive the amplification circuit inside the microphone and amplify the weak electrical signal to a sufficient level for subsequent circuit processing or output.

Bias voltage: The electret film in the electret condenser microphone requires a stable bias voltage to maintain its normal working condition. This bias voltage is usually provided by an external power supply to ensure that the microphone maintains stable performance under various environmental conditions.

Electret condenser microphones usually require an external power supply to provide the necessary energy to drive their internal circuits, amplify weak electrical signals, and maintain their normal working condition.