A driver unit for a square planar diaphragm type loudspeaker system in which a voice coil bobbin attached to the square planar diaphragm is supported by a corrugated damper the other end of which is attached to a heat conducting support whereby heat generated within the voice coil of the speaker can be readily dissipated. A square magnetic circuit is provided including a plurality of straight magnetic circuit sections positioned along corresponding sides of the square planar diaphragms. Each of these straight magnetic circuit sections includes a pair of parallel plate members along inner walls of which opposite plurality magnets are disposed and with a yoke connecting the opposite ends of the plate members. The voice coil which is attached to the voice coil bobbin is disposed in the air gap between oppositely disposed magnets. The damper support is mounted on the outer plate member with a flange portion extending over the upper edge of the outer plate member and having an upper flange portion to the upper surface of which the damper is attached. The damper is formed of a corrugated section of treated cloth which has no elasticity in its longitudinal direction but which is free to move in a direction perpendicular to the plane of the diaphragm.