A composite loudspeaker diaphragm is disclosed having first and second substantially flat carbon fiber skins, and a honeycomb core sandwiched between the first and second carbon skins. In a preferred form, each carbon fiber skin comprises a sheet formed of primarily unidirectional carbon filaments bound together by an epoxy resin. In the preferred embodiment, the honeycomb core is formed of nomex, and is glued with epoxy to the first and second carbon skins, and then heated. The sandwich diaphragm is manufactured so that the direction of the carbon fibers of the cross plies of each outer skin are out of phase relative to each other, preferably in the range of approximately ninety degrees. The improved diaphragm is used in an flat-panel loudspeaker system having improved performance at higher frequencies.