Microphone

Microphones are transducers which convert the mechanical energy of sound into the electrical energy of a signal. They can be used to transmit sound, as in telephone or radio broadcast applications; amplify sound, as in a public address system or a hearing aid; or record sounds, as used in audio engineering and film.

The most common microphones in use are the dynamic microphone, condenser microphone, and piezoelectric microphone, each of which vary in their methodology used to convert the sound to electrical signal.

Dynamic microphones are perhaps the more common of the three, and use a coil suspended in a magnetic field to generate the signal. The vibration of the sound moves a diaphragm to which the coil is attached, which generates a current as the coil moves in relation to the magnetic field.

The condenser microphone goes away with the coil and magnet and instead uses the diaphragm itself as a capacitor plate. When the diaphragm moves in relation to the other side of the capacitor which is fixed, it causes the capacitance to vary with relation to the sound frequency, and a signal can be extracted by this varying capacitance.

Piezoelectric microphones take advantage of the piezoelectric quality of some materials, which causes them to produce voltage when pressure is applied to them. A crystal with piezoelectric properties produces varying voltage from the air pressure in sound waves, which can then produce the signal desired.

• Wikipedia - Microphone