Abstract: A bass unit for a loudspeaker system which has a pair of loudspeakers mounted one behind the other in a casing to define a chamber of air therebetween. The loudspeakers are operated in phase with one another so that the pressure of air in the chamber remains substantially constant and the loudspeaker which is mounted on a front wall of the cabinet thus operates under substantially "ideal" conditions. Any changes in sound pressure within the chamber represent distortion components and are absorbed by a curtain of absorbent material in the chamber by a filling of absorbent material.