Abstract: A loudspeaker comprising a horn waveguide having a throat and a waveguide surface; an acoustic radiator assembly, located at the throat of the waveguide, comprising a diaphragm having a rigid acoustically radiating surface shaped as a section from a toroidal surface for generating acoustic wavefronts, the waveguide surface being adapted to match the shape of the wavefronts coming from the assembly.

Abstract: An audio system comprises three or more loudspeaker units and a source of four or more audio channels, each loudspeaker unit comprising a monopole loudspeaker and a dipole loudspeaker, or a pistonically driven diaphragm loudspeaker and a resonant panel loudspeaker. The system may be arranged such that, for any position relative to a listener at which a loudspeaker unit is situated in use, sounds emitted in response to signals carried by the audio channel for which the designated intended output position corresponds most closely to the position of that loudspeaker unit are emitted from the monopole loudspeaker or pistonically driven diaphragm loudspeaker of that unit. If a loudspeaker unit is not situated approximately at such a position, then sounds emitted in response to signals carried by that channel may instead may be emitted from the dipole loudspeaker or resonant panel loudspeaker of that loudspeaker unit.