(Yes, another one of these threads...) I will soon have a 21 x 15' room which will contain both a home theater setup with ELAC F6 floorstanders and a 12" sub, as well as a 4x12" Mesa half stack. I'm not concerned nearly as much with the quality of sound in the room as I am with the penetration of that sound throughout the rest of the house. Insulating WITHIN walls is unfortunately not an option as it's just too late for that and access within the walls will be extraordinarily limited. What I'm primarily concerned about is a single 15' wall which borders the part of the house I'd like to disrupt the least. That wall will be behind the guitar rig, meaning the 4x12 will face 180 degrees away from it. I THINK what that means is the wall will primarily receive bass from it (it's a fully closed back cab, so even that will be minimal). The wall will, however, be roughly 15 feet away from the front and center channels of the HT setup. The HT speakers will rarely top -20 db from reference, so perhaps the guitar rig remains the issue--even it will rarely exceed 85db. There are all kinds of suspiciously cheap egg carton or wave-style 12x12x2" squares available on Amazon. If they manage to dampen the sound that hits the key wall in the neighboring room by even 3db, it's worth using over nothing. However, I'd really like to have a more effective solution. I don't care nearly as much about sound quality within the room as I do not disrupting the rest of the house. What would you do with this wall 15x8' wall? I realize other acoustic properties of the house will affect matters and that the construction of the wall changes, but let us assume for simplicity that all I can do is improve the wall from within the room itself. FWIW I am already planning to have bass traps in every corner. If it comes down to it, I'd rather dampen highs and mids. A generally muddy resonance in bordering rooms is, in my experience, far less annoying than an articulated sound complete with treble which demands your attention. Note that the cab has Vintage 30s in it which put out some serious highs... As for my budget, it's flexible but I'd really prefer not to spend more than $1000 on 15x8' wall... I could easily afford enough Amazon 12x12x2" tiles (of questionable density) and surplus carpet to go behind it, but I'm sure you will have better ideas. Should I look at covering my own OC 703 panels instead and stacking them floor to ceiling?