I am not a box building expert but if you only have one chamber the box is more likely to explode...by that I mean because there is no other reinforcement (i.e. middle seperator between chambers). You could put some braces in to reinforce and still share the airspace but then the subs are not in the recommended size enclosure
example: recommended sealed space for 1 sub is 1 cubic foot and you have 2 subs in a box that is 2 cubic feet total (1 cubic for for each sub) it will cause the subs to function more poorly.
Not to say this can't and hasn't been done but it would be more beneficial to have each sub in its own seperate sealed/vented/banpass section/chamber of the box. Maybe someone else might be able to explain it better. HTH
