An acoustic horn arranged to be fastened between a cabinet of a loudspeaker enclosure and an outer casing, the horn presenting a shape and/or dimensions that depend on the outer casing, the acoustic horn being arranged in such a manner that when the acoustic horn, the cabinet, and the outer casing are assembled together its inner face is in contact with the cabinet so that its inner edge surrounds a diaphragm of the loudspeaker and its outer face is in contact with the outer casing in such a manner that a hole set having at least one hole in the outer casing lies inside an area defined by its outer edge, the horn thus being arranged in such a manner that its inside peripheral surface guides sound produced by the loudspeaker towards the outside via the hole set having at least one hole in the outer casing.