A dipole speaker with a transducer that uses the audio signal to vary the strength of an electric field which, in turn, induces vibration in a metallic or metalized membrane. In principle, it is the reverse of an electrostatic microphone, and very different from the more common electromagneticelectro-magnetic voice coil arrangement. Used for consumer equipment as the power output is low. Electrostatic speakers are usually quite large, such as 6’ high by 2’ or 3’ wide. They are always direct radiators, and they must be large to attain reasonable efficiency at low frequencies. The radiation pattern of an electrostatic speaker in a free-field is similar to that of a figure-eight microphone. Because of their large size, electrostatic loudspeakers tend to become very directional in the high-frequency range. They are also characterized by a low impedance, and this is problematic for some amplifiers. See also planar loudspeaker.