Abstract: 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 cardboards 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.