Originally Posted by mtbdudex
Some more progress on integrating the wides into the side walls:
My LH wall is outside foundation wall, it is engineered concrete with concrete studs that are 9 1/2" deep and 24" center, so I built a box to insert into the cavity as shown.
Leftover 3/4" thick OSB works nice, it takes drywall screws pretty good.
For the back I had 1/2" birch ply, so used that, since I did not have a 21" x 12" piece of OSB, wood scraps always come in handy.
Glue and screwed, box 100% sealed.
I had to contend with HVAC 8" dia pipe, so the box "wrapped" around that for maximum position ability - angle wise - of the speaker
Used pressure treated 2 x 4 for top/bottom support, as they contact the concrete studs, and then able to also screw into the RH side concrete stud, it is faced with 1" thick wood strip for drywall attaching.
Box is very sturdy in there.
Here is RH side, primed shows some spots I'll add more spackle and re-do, hey I'm not the best at mudding
Honestly, making the speaker box shelf outside of the wall and then "plugging it in" was much faster on the LH side than building it "in wall" as I did on the RH side, a small lesson learned.