A flat panel rectangular or elliptical loudspeaker has one or more anisotropic diaphragms (14, 15), made of double skinned fluted polypropylene copolymer (core flute) or corrugated cardboard, having a longitudinal bending strength greater than the transverse bending strength. The diaphragm is vibrated by a driver unit (16) which comprises a magnet (17) and voice coil (18). In this version the magnet (17) is mounted on the rear diaphragm (15) and the voice coil (18) is mounted on the front diaphragm (14). The two diaphragms (14, 15) are mounted at their edges to a frame (11) with the driver unit (16) mounted in the space enclosed by the frame and the diaphragms.
