A low frequency exponential/hyperbolic hybrid folded horn enclosure intended for use in proximity with at least one planar surface, such as a floor, ceiling, or wall, with access to the horn throat from the top of the enclosure. The horn is bifurcated at the throat and folds horizontally around a central trapezoid-shaped vertical back chamber which is reflex ported for enhanced low frequency response below the frequency cutoff of the horn. The back chamber outer sides define part of the horn channel, resulting in a relatively simple structure with a small footprint and no void internal space. The throat exponential expansion cross-sectional area is consistently maintained while the proportions of the throat channels are elongated to the height of the enclosure.