I'm not too sure about this tendency to talk about "acapella" instead of "unaccompanied". I think that the term should be restricted to a certain sort of pure voiced singing that might be appropriate in a church setting.

If you start using " acapella" as if it meant the saame as "unaccompanied" you get the absurd (to my mind) situation where you call the sinmging of sea shanties and rugby songs "acapella", just because no-one's playing any kind of intrumental accompaniment.