A loudspeaker enclosure of the acoustic suspension type has a hollow interior of a generally spherical shape, and the enclosure is formed of polyurethane foamed plastic in which the volume (V) of the enclosure interior is determined according to the following empirical formula:V=[MD].sup.3where M is the distance between the limits of mechanical excursion of a given loudspeaker mounted in an aperture in the enclosure as the diaphragm of the speaker is moved under a constant mechanical force, and D is the diameter of the loudspeaker.