Abstract: A low frequency loud speaker is disclosed for use in a room at the intersection of two, mutually perpendicular planes, such as a ceiling and a wall, a floor and a wall or two walls. The speaker has a back air chamber within which an electrically-driven diaphragm, centered on and facing a vent cut through the chamber's rear surface, projects low frequency sound waves into the throat of a compact, bifurcated, exponential horn folded around the sides of the chamber to the mouth of the horn at the back of the speaker. The back air chamber receives sound waves from the rear face of the diaphragm and causes these back waves to acoustically activate the air in the vent above and below the diaphragm.