An apparatus comprising: a first substantially horn shaped structure configured to couple and amplify sound from a first speaker of a further apparatus; and a second substantially horn shaped structure configured to couple and amplify sound from a second speaker of the further apparatus, wherein the first and second substantially horn shaped structure each comprise a mouth portion with a physical separation dimension greater than a physical separation dimension of the first and second speaker acoustic outlet of the further apparatus.

A loudspeaker includes a horn and a compression driver in a shallow package for installation in a wall, e.g., a four inch wide wall. The total depth for this loudspeaker may be about 3 and inches. A low frequency speaker can be supported by the frame and dimensioned to be mounted in a wall. The horn can be supported by the frame positioned by the speaker. A compression driver is supported by the frame and acoustically connected to the horn. The horn acoustically loads the compression driver to provide a high dynamic output and a high sound pressure level with controlled acoustic directivity.

A speaker includes: an open-backed speaker unit, a housing, and a fin unit. The housing is disposed so as to cover a rear side of the speaker unit, and forms a back cavity with the speaker unit. The fin unit is disposed in the back cavity, and includes an annular or arc-like fin, which approaches a rear side of the housing as going from a center of the speaker unit toward an outer diameter side thereof, and expands in diameter as separating from the speaker unit.