How Microphones Work
Microphones
Both use this exact same principle, but in opposite ways. In the loudspeaker, a coil of wire is wrapped around a strong magnet with a small air space between them. The coil is attached to a cone of stiff paper or similar material. An electric current is applied to the coil and it moves within the magnetic field, moving the cone with it, displacing air and producing sound – Magic! Microphones are usually connected to the recording interface with cables, but more recently, wireless microphones are becoming more common.
Dynamic Microphones The opposite is true for the dynamic (moving coil) microphone. Sound pressure moves a membrane or diaphragm (small cone) which moves the coil in the magnetic field. This induces a small electric current in the coil. Isn’t physics wonderful!
Ribbon Microphones Ribbon microphones work in a similar manner. The ribbon is a thin corrugated strip suspended within a magnetic field. As sound pressure moves the ribbon, so an electric current is produced within the ribbon. Ribbon microphones tend to be more delicate than other kinds of mic's and are exclusively used for studio work, and you need to make sure you don't drop them!
Condenser Microphones The condenser microphone works on a different principle. Two thin plates are mounted close to each other; one is fixed and the other, the diaphragm, is suspended and free to move. Sound pressure falling on the diaphragm causes the distance between the plates to vary and hence causes a change in capacitance between them. If the plates are biased with a fixed charge (hence the need for phantom power), the variation in capacitance creates a change in voltage proportional to the variation in sound pressure – More magic! Condenser microphones come in two basic forms; large diaphragm, and small diaphragm. Large diaphragm mic's can stand higher sound levels, but small diaphragm mic's generally have a better frequency response.
Electret Microphones A relatively recent introduction is that of the Electret microphone. It works in a similar way to the Condenser microphone in that sound waves cause a change in capacitance which in turn produces a voltage. However, the electret micprophone uses a ferro-electric material as the transducer, that is permanently charged, so no phantom power is required for this purpose. However, since the voltage generated is so small, electret microphones do require internal amplification. Sometimes this is via an internal battery (and since the amplifier uses so little electricity, it can last for many months), or it can use the phantom power supply that would alternatively power condenser mics.
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