Well, I last night I made my 12 'backer boxes', which maybe I would call more of a 'Backer Sandwich", it took about an hour in total... This relates back to Post 427/29 (&448)
I ended up with this configuration:
3/4" MDF Solid with Green Glue
5/8" Drywall Solid w Green Glue
3/8" Drywall w/ Hole w Green Glue
3/8" Dyrwall w/ Hole
I used this based on the concern expressed about Fire hazard, figuring the fire-rated drywall would be the way to go - and frankly, much easier to 'cut' that as well, so, doing it again - I probably would do two layers of the 5/8" solid Drywall.
Then with the two ceiling layers of 5/8" drywall, the box depth will match my ceiling depth with my 'backer' boxes.
Here are the parts in there individual piece forms...
Here are the parts with Green Glue applied... "Learning", I applied the GG to the 'fronts', defined as the part on the Theater side vs the 'ceiling/subfloor' side of the MDF, 5/8" Drywall, and the 3/8" Drywall... This meant when I did the 5/8" drywall 'all over', the 3/8" light box 'hole' had GG all over. So, to do it again, I would put the GG on the 'theater side' of the two 3/8" drywall layers, and the theater side of the 5/8" drywall layer..
Here is what the 'final' product looks like. These will be installed onto the subfloor side of the drywall in the correct locations before the Drywall is lifted into place. The circle at the top is the Surface Mount LED light.
We'll see how this all works out.