A long time ago, a very clever guy called Alexander Fleming discovered that if you introduced an electric current into a magnetic field, you produced motion. Conversely, if you moved a coil of wire within a magnetic field, you induced an electric current within the coil of wire. Most people are grateful for this invention for the creation of the electric motor, but we audio addicts are much more grateful for the creation of the loud speaker and the dynamic microphone.
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!
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!
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