Originally Posted by WagBoss
12" thick absorption panel? Why so thick? Even 4" of roxul block 100% of 125 hz and above. Do you have more explanation for that? How tall/wide of a panel would I need for that? Would a diffuser work behind instead of an absorption panel? I already built my absorption panels and wasn't planning on building more
You're too close for diffusion.
The thickness is to lessen the freq response peaks and dips at the LP. I'm not sure 4" of anything is full to 125hz, but the point is attenuate as deep as possible in frequency, to retain punch and FR smoothness commensurately.
I'd go 12", yes. If I had Safe-N-Sound, or 703 I'd use it, otherwise I'd likely compress some fluffy E-Cose style glass fiber, and go that route.
The approach I'd take would depend what material I had.
Here's some guidelines when considering thickness available for the treatment area;
For 4" thick, the dense stuff (OC703 or equiv) is the best.
For 4"-12" use 4" of 703 like and the rest air gap, or use Rockwool Safe-N-Sound up to 12"
For 12" and up, fluffy fiberglass approach works great.
Also, comparing equal amounts of volume doesn't work. Like 12, 4" traps vs. 6, 8" traps,... thicker isn't necessarily better. Oftentimes, covering more surface area and spreading the material around performed significantly better.
These suggestions aren't hard and fast rules. 8" of 703 still works great, perhaps it's just not the best use of the material. The air gap is the performance multiplier,... mind the gap