Ideally the housing of a loudspeaker does not contribute to the overall sound of a loudspeaker. The sound is supposed to be produced by the loudspeaker elements only. The ideal case is a loudspeaker not bigger as a point in space reproducing all audible frequencies. This reproduction should be as linear and dynamic as possible to mimic the original source of the sound. What we want is the same sound experience as the original.
Reality is a little bit different. Apart from irregulrities and distorsions of the elements, loudspeaker housings produce sound by themself.
The whole housing might vibrate or parts of it. Vibrations mean sound.