Yeah - an older thread, but a cool subject.
Anyways, if you're interested in making diffusers I would suggest you use
PL Premium Polyurethane Construction Adhesive. This stuff is amazingly strong - and will fill a gap or void quite well too.
I've used this stuff to build a bass speaker cabinet and am currently building some sound absorption panels and continue to be amazed at how strong this stuff is. ... and no, I am not affiliated in any way to Loctite.