It took me another month to complete the room, but I am pleased to say that now it's finally ready!
I'll break down the steps that followed from my last "making of" post. Basically, the room was structurally ready with all the walls, ceiling, and door so it was sound proofing and final touches that remained. I also spent went to the US for a 10-day trip with some friends which ate away some of my time... and funds...
At this stage, the sound is like an echo chamber. A rectangular room with flat plaster board surfaces and a hard floor. I also bought 10W LED-lights (750 lumen each) that I put up into the corners and I put some simple electrical wiring up. I ended up opting for normal extension leads because I want to be able to take the lights down and relocate them in the room if necessary. The reason I went for LED-lights are primarily because they are silent (no humming) and they don't generate much heat which benefits both the room temperature and also it won't heat up the metal of the light which in traditional lights have a tendency to start producing clicking sounds as the metal contracts/expands.
A big 2 pallet shipping arrived from http://thomann.de. I ended up buying 40 of their 1x1m 80mm thick sound absorbing SA-P80 foam along with 16 large foam CBT-37 bass traps CBT-37 bass traps. For additional sound proofing I also got 10 Stairville Acoustic Curtains to line the interior walls with.
I used about 10 tubes of "Akrylfog" to seal any and all little corners where the plaster boards met the wood frame - not too sure that it was worth the time it took, but at least I know it's done and if it prevents even the slightest sound from entering / exiting the room I guess I'm happy with that =)
I moved on to put up the insulation in the room. Since I had spaced all the wood beams 60cm apart it fit perfectly with the standard size of the insulation slabs. I didn't go with rockwool because I didn't know where to get it or how much it would be, so I bought standard glass-based 120mm thick insulation called Space Slab (it said it had good acoustic and sound absorbing properties.) I really hate putting up insulation, especially in the ceiling. I had a mask to cover my mouth, a hoodie over my head, and goggles when working on the ceiling. Still, the fibers go everywhere and I couldn't wait to get finished. Finally I was:
I recorded some hand claps during all stages of the insulating process and this insulation really eat up the echo totally. I was very pleased with the sound and just speaking or being inside the room had a really strange feel to it - the sound was extremely dead with no echo. Maybe not the most pretty walls, but there was still many layers to go.
Next step was to put up the Stairville Acoustic Curtains. I didn't want to put any plaster boards up to internally to cover the insulation because the hole idea was for the sound to get eaten up by and absorbed into the insulation. The solution was to staple up the sound blankets using a staple gun. Doing this on my own was a real challenge and a pain in the XXX. Especially tricky was the blanket in the ceiling because A) it had to be put up perfectly in line, B) few stables would not hold the weight of the blanket up, C) even the slightest offset would result in the opposite corner not having enough blanket to cover, D) the blankets are heavy so resting them on my shoulder as I try to staple it upwards in a straight line in darkness (since I was under the blanket) was far from easy - but I got through it.
It took 2500-3000 staples to put up the double layers. I stapled them directly into the stud beams and the first layer was the worst since I was working directly onto the insulation (dusty and itchy fibers!) and the second layer was also worst come to think of it because it was more difficult to feel the wood beams and staples didn't necessarily reach that well through multiple layers of sound blankets, especially in the corners where it was overlapping. Thomann had missed to ship one of the blankets in the order as well so I ended up taking cutoffs to cover the second layer of one of the short walls. They sent me the missing blanket without any hassle but I wanted to proceed with the build - always good to have a spare blanket that I can use in the field.
Interestingly and surprising (well, maybe no that surprising) there was an echo in the room again with the blankets up. The sound will bounce off the blankets compared to how well the insulation was absorbing the sound waves. Far from what it sounded with the plaster boards, but enough to notice that there was an echo again. Still, I think that it's the better option because the little sound that bounced means that it'll keep external sound from coming into the room as well. The first layer of blankets I put up quite stretched which was a mistake because it'll act like the membrane of a drum. I deliberately didn't stretch the second layer which I hope helped a bit.
It was finally time to put up the sound absorbing foam. Since the blankets were stapled directly onto the wood beams I had limited options to install the foam panels. They weren't as stiff as I first anticipated so the ceiling panels were more difficult to install. I ended up going for 4" (10cm) long nails that I hammered through the foam into the wood framework. I had to feel my way to know where I could put the nails and generally I used only 4 nails per panel. Some of the panels were only covering one single wood beam and in the ceiling this was especially a problem since the entire panel would drop down on either end. To solve this I put 6 nylon lines across the length of the room that I secured on either end and on all ceiling beams (every 60cm) - that kept the panels up. There is a bit of a wave-pattern in the ceiling due to gravity but I think that is actually beneficial if anything - sound bounces more off straight areas.
The panels were up and again the echo was gone. Not sure how it exactly compared to just having the insulation exposed but I will be able to compare that when I process the audio recordings and footage that I took between each step. Now it started to look like the sound recording room I had envisioned.
Final touch to the room was to add the carpet on the floor. It'll take the final slap echo that the flat epoxy floor produces. I made sure to also cut along the length of the room on both sides and across one of the shorter sides because now I can roll the carpet up to expose a large portion of the solid floor when I need it to smash stuff on, like glass, melons, computers, plates, TVs... you get the point =)
I should also mention that the trickiest thing of the entire room build was to figure out how to get the door to seal properly. I have put rubber strips on the door frame onto which the door shuts, but it needs to be pulled close with a decent amount of force (otherwise it'll glide open.) I'll put a separate post on that someday how I solved it. The main thing was that the door shouldn't only be sealed from the inside, in case of an emergency, so whatever mechanism I went for had to be openable from the outside too. With the door being thicker than standard doors normal handles was no option.
Finally, here are some pictures of the final room and an updated equipment picture. Let the recording begin!!