In loudspeaker design, a dipole radiator is a system which radiates forwards and rearwards with equal energy, but with opposite polarity. Examples of dipole radiators are electrostatic loudspeakers and planar speakers. Some cone-type speakers have dipole radiators. For a dipole radiator to have adequate low-frequency response, it must be very large to prevent the rear wave from canceling the front wave. Also, the dipole radiator must not be placed close to and parallel to a wall, working best when not near reflective surfaces.