A Music Room, the plan, and a couple of questions

G'day everyone, Dex from Australia here, with a plan of attack and a couple of questions if anyone has time for answers. But first a thanks to all who have contributed to this forum, it has made invaluable reading as I plan for a small music (or noise) room in our basement. The main aim here is the sound-isolation of this room so my son and I can go berserk on guitars and drums without disturbing the rest of the family. Firstly a broad description of the area in the basement I am using and the plan of attack. I was thinking of using the "room within a room" principal, and the area I am using is 9' wide by 21' long by 7'7" in height. We'll label the existing walls (the "outer-walls" if you like) ABC&D going clockwise: outer-wall-A is 21' long, made out of besa-blocks (cinderblocks in the US I think), and is an internal basement wall backing onto another part of the basement (ie doesn't have dirt behind the wall). Also has an existing doorway which will be the entryway into the music room. outer-wall-B is 9' long, made of cinderblocks, and is an external basement wall, i.e. has dirt on the other side of the wall. outer-wall-C is 21' long, made of cinderblocks, and is an external basement wall, i.e. has dirt on the other side of the wall. outer-wall-D doesn't exist yet, and needs to be built. i.e. outer-Wall-D will essentially partition a larger room within the basement into the music room and a smaller area that will be used for storage. The outer-ceiling is a slab, on the other side of which is a living area upstairs, hence the need for some sound isolation. The floor is a concrete slab, on the other side of which is dirt (I should hope) Given that outer-walls AB&C are essentially there already, I was going to use some CSR-Soundscreen on wall-A seeing as it backs onto the rest of the basement, and on the ceiling as well seeing as it backs onto the living area upstairs, but I was going to leave walls B&C as they are seeing as they back onto dirt, which (should) effectively absorb the sound going through these walls (?). Outer-wall-D was going to be of the same construction as all of the inner walls, which would be two layers of 3/8" drywall with CSR-Soundscreen-insulation. As mentioned above, the inner walls (ABC&D), and the inner-ceiling are to be two layers of 3/8" drywall with CSR-Soundscreen, mounted on a frame made of construction-timber (4x2 pine). This "inner-frame" would sit on some 5mm rubber strip to isolate it somewhat from the floor. The inner-floor? well from what I've read here on this forum it sounds like there is little point doing a floating floor unless I knew what I was doing with it (nope I don't), and at 7'7" in total height to play with, I don't have enough to be raising the floor any, so the "inner-floor" was basically going to be a layer of rubber-backed carpet tiles that have been uselessly taking up space my basement for years (not anymore!), a layer of carpet underlay on top of those, and a layer of carpet on top of the underlay. between each of the inner-walls and outer-walls (and inner-ceiling & outer-ceiling) I was going to leave a gap of 4" of air. So for example the whole of Wall-A (including inner and outer), going from the outside to the inside will be: cynder-block,CSR-Soundscreen, 4" of air, CSR-Soundscreen, 3/8"-drywall, 3/8" drywall. I'd like to be able to leave more of a gap than 4" as I've read on this forum that bigger gaps between the innner and outer walls is better, but as you can see above from the dimensions, I don't have terribly much room to play with here. So the above is the plan in a nutshell, and the questions are below. Apologies if they are answered elsewhere in the forums, I read a lot, and maybe just didn't come across specific answers to these questions: -is it OK to leave outer-walls B&C without any soundscreen-insulation seeing as they back onto dirt? Or should I use soundscreen insulation on them -should I be using soundscreen-insulation on outer-wall-A and the outer-ceiling which back onto other parts of the basement/house, or am I wasting my time and money here. -Is soundscreen-insulation worth the extra 50% cost on top of normal standard fibre-glass house insulation (which I guess is primarily thermal in purpose)? -is 4" of space/air between outer and inner walls going to be enough? - Is my approach broadly OK, and are their any suggestions anyone would make? I've read these forums, and my solution above seems right to me for my budget, but am happy to hear any feedback. a couple of side-notes: the CSR-soundscreen I am using will be the R2 stuff at the link above. Also if anyone is interested I will post some pics as we progress on the project. Thanks for reading, Dex

welcome. the challenge is that the insulation will not isolate... so you need mass all around - ceiling and walls to make it work. in the air space for the new isolation walls - use lighter weight insulation 15-24kg/m3 will do it. assuming the remaining block walls meet your requirements and the end result is enough isolation, use the heavier rigid insulation (48kg/m3 or so) to make your acoustic treatments - corners trapping, first reflection points for your mixer desk, and scattered absorption around to balance the room. if you're looking for integrated treatments like slats and polys etc, that is an option.