Microphones are pressure transducers, and are used to convert sound pressure levels into electrical signals. The following types of microphones can be used to convert sound pressure waves into electrical signals: electromagnetic, capacitance, ribbon, crystal, carbon, and piezoelectric. Figure 12.8(a) shows the cross section of a dynamic microphone, which consists of a coil in a magnetic field driven by sound waves impinging on a diaphragm. An EMF is induced in the coil by the movement of the diaphragm. Figure 12.8(b) shows the cross section of capacitive microphone, which is an accepted standard for accurate acoustical measurements. Sound pressure