Abstract: A resonant loudspeaker system which produces improved reproduction of low frequency sound comprises a coupling chamber which encloses the rear of the low frequency driver and which contains two additional openings in which are suspended diaphrams free to move but coupled together so that the forces on them are in opposition. One of the diaphrams is baffled and the other is free to radiate. The air in the coupling chamber when excited by the low frequency driver can only act upon the difference in the areas of the diaphrams, but the radiation produced by the diaphrams is determined by the unbaffled area. The radiation from the rear of the low frequency driver is thus amplified permitting an improved combination of low frequency response, low distortion, electrical efficiency and physical size to be achieved.