(1) The principle of moving coil microphone:

　　A microphone is a device that converts sound into electrical signals.

　　The following is the construction principle diagram of the moving-coil microphone, which is made of electromagnetic induction phenomenon.

　　When sound waves cause the metal diaphragm to vibrate, a coil attached to the diaphragm, called a voice coil, vibrates along with it.

　　The voice coil vibrates in the magnetic field of a permanent magnet, which generates an induced current (electrical signal).

　　The magnitude and direction of the induced current vary, and the change in amplitude and frequency is determined by the sound wave. This signal is electrically amplified through the amplifier and transmitted to the speaker, from which the amplified sound is emitted.

　　(2) Principle of capacitive microphone:

　　As shown in the figure, Q is an insulating bracket, a thin metal film M and a fixed electrode N form a capacitor that is charged by a DC power source.

　　When the sound wave causes the diaphragm to vibrate, the capacitance changes, and a changing current is formed in the circuit, so that both ends of the resistance R output the same voltage as the sound change law. Its advantage is good fidelity.

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