Abstract: A loudspeaker enclosure comprising a cabinet to be located adjacent to a wall and having a horn contained therein driven by two loudspeakers oriented at right angles to the axis of the throat portion of the horn in which they are located and on opposite sides thereof, the speakers being substantially aligned in close mutual proximity and driven out-of-phase to provide adequate drive to the horn while tending to damp each other's excursions, and the horn having an internal expansion air column which extends into an external expansion air column bounded by the cabinet and by the wall and floor of the room, the external air column having a catenoidal rate of expansion which terminates in very rapid flaring closely matching the high expansion rate of the air column into the room which results from placing the horn at a mid-wall location, as distinguished from a corner-wall location.