Abstract: The present invention relates to a compound loudspeaker. In the loudspeaker, the L.F. drive unit has a curved flexible diaphragm whose shape is determined such that it optimally controls the directivity of the compound loudspeaker to produce matched directivity of the L.F. and H.F. drive units. The L.F. diaphragm drive unit radiates sound by the controlled flexure of its diaphragm and thus, eliminates the need for a flexible rolling seal at the edge of the diaphragm. This allows for a continuous smooth surface to exist between the H.F. drive unit and the exterior of the loudspeaker, thereby greatly improving its radiation characteristics.