Wayne Parham Messages: 18748 Registered: January 2001
Illuminati (33rd Degree)
I use R13 (which is about 3" thick) on the back, top and side nearest the port. I also use a sheet that spans the cross-section, glued on the brace between the woofer and tweeter, which is also between the woofer and port. Honestly, this is probably the most important sheet. It does a great job of damping internal standing waves that would otherwise cause some lower midrange ripple.
This has been discussed on the forum, although I'm sure it is lost in the thousands of posts. It is mentioned in the plans.