When hanging bookshelf speakers(6.5" woofer) without spacers on back, what is the best thing to add to back of speaker, to leave a little space for wiring to sneak out? I have 1 speaker that the wiring has to come out from behind and up thru my ceiling tile. I was thinking of some sort of rubber spacer. Also, is it best to use a rubber spacer, etc. even when speaker rests flat against drywall for vibration reasons? Thanks.