Now to the speaker backer boxes. Using IB3 clips to decouple the boxes from the framing cavity in the wall
Due to the weight of these boxes, which are well over 45lbs., I decided to use 3 clips for both the top and bottom and one clip each for the sides to stabilize.
First I measured the top side of the box + 3/4" on each side of the 2x6. The 3/4" on each side will provide enough of a gap so that the side IB3 clips will fit.
I decided to go with one clip on the back, and one each on the sides of the 2x6. To create more stability I attached the side clips a little to the front to form a type of triangle pattern.
I marked out the exact locations of the clips
Then attached the clips in a triangle pattern
Fastened the 2x6 to the top of the backer box
Again, there was a 3/4" gap on each side of the box so that the side clips could be attached. The 3/4" gap was just enough to fit the IB3 red gasket into. In this picture you can see all 4 sides are attached. The sides have one clip. The top and bottom have three clips, the one visible on the back and one each on the sides.
For position of the side surrounds I want the front row to be the money seats so I placed the boxes about 5 degrees back from the listeners head position of each side wall. I have the center of the backer box right at 6.5'. To ensure all boxes are exactly the same height all around the room I used my laser level
From this picture you can see that all sides are completely decoupled from the 2x6 framing
And the finished box
The rational behind the depth of the box is this; Each box is 7" deep. I have a 2" gap from the rigid foam to the 2x wall. So that 2" + 3.5" (2x4) = 5.5". That leaves 1.5". Clips, channel, and DD is 1 5/8", That gives me within 1/8" of the finished wall. That small seam will be sealed with acoustic caulk. Acoustic treatments will be 2", so this will give me 2" from the speaker to the GOM fabric. Right where I want to be. The boxes are very stable in the wall. I will most likely fill some of the box with Polly-fill. In previous posts I went into the design of the boxes. The front cover will be a custom template for each speaker to fit into. Each Triad will fit into the 1/2" MDF front. That 1/2" cover will sit flush. If I want to change speakers out in the future I will just rip another 1/2" MDF cover front template