I've been working to empty this room for the last couple of weeks in order to get on with the soundproofing. It's involved a huge amount of manual labor. The simple fact is that this room has been the most intensive testing room of the 3 we have, and also the most packed, every wall lined with shelving and storage. Emptying has meant squeezing the contents of 3 rooms down to 2 -- necessary because once it's done, this room will only contain a table, the mic and the item being acoustically tested. It was truly a grind, and the other 2 rooms still look like a tornado came through.
The room was mostly emptied by mid-week last, and I spent the last couple of days sealing up the outside perimeter wall. That's the one with the window. The concrete block foundation wall comes up about 4 feet from the floor, and with the drywall, 2-by-4 studs etc, the overall thickness of this (lower) half of the wall is well over a foot, probably 14".
The upper half of the wall is only half that thickness, and contains no concrete, which provides much higher sound attenuation. This photo, posted earlier, showed how I sealed the window with a 1.2" thick piece of medite board. (see my June 14 post)
The photo below shows the 8" deep ledge along that wall.
Here's how I did it:
1) created framing for the new skin to be screwed into place. I used 1.25" thick pieces of wood, as well as 2x4 and 2x6 pieces for an additional center stud.
2) lined the "ledge" space with 8" thick 48"x16" pieces of Ultra Touch recycled cotton batting insulation. 7 pieces were needed. One had to be cut in half -- amazingly tough stuff, took nearly 10 minutes with a new utility knife.
3) screwed in 4 panels of 3/4" medite board to cover the 4'x10' area. I was originally going to use a single 4x10' sheet, but the 10' stuff is only available at certain commercial lumberyards.... and I because I was working mostly alone, trying to lift or handle one would be impossible. Besides, I don't have a pickup truck to transport the stuff. Even the 2'x5' pieces that were cut for me at the lumberyard are not easy to handle when you have to get them up above shoulder height -- but I'm certainly no Hercules.
Why not drywall or QuietRock? Well, both of these materials create really fine nasty dust that I want to avoid that as much/long as possible. I don't think medite board is quite as soundproof as QR, but it's pretty dense, with excellent internal damping, and there's also that 8" thick insulation.
Since I wanted the entire assembly to be taken apart relatively easily if necessary, I used no adhesives, made sure not to strip any screw heads with power drills, and applied foam insulation strips between the panels and the framing to make an acoustic seal.
This photo was taken just before I made a quick audio recording with the new ACO Pacific mic to show acoustically where the room is at this point.
Here's the recording
-- I recommend you right-click and save to your own computer before playing, as it's 3 megs.
As I said in the recording, the sound attenuation in the room is good enough that I feel compelled to line the interior of the room with the 700 lbs of Ultra Touch cotton batting awaiting in the garage -- before building the room-in-a-room. If the noise attenuation is not good enough, then it's not that difficult to remove the batting to build that second inner room. But if it is
good enough, then I will have saved a couple of weeks of strenuous labor. Well see. It might be done by the end of the day -- maybe around 10pm if I keep going at it all day.