A loudspeaker system of improved clarity, coherence and uniformity of energy distribution containing mid frequency sound chambers with an annular input and approximately rectangular output for use in multi-way co-axial horn loaded line array systems. The sound chambers propagate the annular mid frequency sound wave co-axially with a high frequency sound wave, gradually changing the cross section of the mid frequency wavefront resulting in co-linear acoustic mid and high frequency wavefronts from multiple devices which range from the shape of a flat ribbon to that of a curved ribbon. The sound chambers may be arrayed contiguously and placed at the entrance of a suitable waveguide to form a wide band width acoustic line source of extended length and controlled beamwidth.