Microphone See Also: Telephone Device (invented circa1877) used in broadcasting, recording, and sound-amplifying (see Amplifier) systems to convert sound into electrical Energy. Its basic component is a flexible diaphragm that responds to the Pressure or particle velocity of Sound Waves. In an electrostatic, or condenser, microphone, two parallel (see Parallel Lines) metal plates ( Electrodes) are given opposite electrical Charges. One of the plates is attached to the diaphragm and moves in response to its vibrations, generating a varying Voltage. An electret microphone, the most widely used type, has a permanently charged dielectic (electret) between the two electrodes. A Loudspeaker reverses the process.