Abstract: A wave guide fitted at the output of a loudspeaker, in front of the membrane or in front of the orifice of a compression chamber, along the axis of the transducer being considered, and comprising a conduit which expands from its input to its output. The area of the output orifice of the wave guide is planar and oblong, that its conduit comprises a passage between the input orifice and the output area, adapted to guide the waves along a general direction from which the shortest paths allowed in the one or more passages are all of lengths which are practically identical from the input orifice to the output orifice of the conduit. The invention is for use in providing sound to large areas.