Hi there Koma, and welcome!
the most important factor was the size of the room, to avoid modal activity.
You can't "avoid" modal activity by changing the dimensions of a room. ALL rooms have modes, regardless of the size or shape. A mode is simply a path that a sound wave can take around the room and arrive back at it's starting point, in phase. What you change by having a bigger room, is to have more modes in the low frequency end of the spectrum, and they are closer to each other. Which is good! In small rooms, the modes are a long way apart from each other (in frequency), and they start at higher frequencies. Which is bad. So it's great that you can have a bigger room, but it will not eliminate modes: it will just improve the modal response.
The slab in my basement is a simple concrete slab which is about 10 cm thick. The outer walls (also concrete) is 30 cm thick.
Excellent! That's very good for isolation.
To obtain the highest possible isolation, i am thinking that the double frame wall is the way to go, although it eats up a lot of space.
You already have one wall: your concrete wall is your "outer leaf". So you only need ONE frame to create a proper 2-leaf system. You do not need two frames: that would, indeed, waste a lot of space, and tit would also reduce your low frequency isolation.
In the celling if possible, i want to install 3 layers of drywall, then insulation, then rc-1 channel ( well we don't really have that in norway, but a Norwegian version of it) and then two layers of drywall.
That would create a 3-leaf system, which would have poor isolation in low frequencies. You should only ever have a two-leaf system, which is the least expensive and most effective.
Based on the information given, what would be the best design for the walls? Is a rectangular shape something i should avoid?
You only have a very small budget for this, so yes, your only option is a rectangular shape. You won't be able to do one of the more complex shaped rooms, such as RFZ, because that would increase the costs, even though it would also improve the acoustics.
(photo of ceiling above)
So you have floor boards (planks) on top of 2x6 or maybe 2x8 joists? You will need to seal that off somehow, and add some mass as well. I would suggest putting two layers of drywall or MDF up there, against those floor boards, holding them in place with cleats nailed sideways into the joists, and carefully caulking all around the edges with acoustic caulk. BUT!!! You will need to get a structural engineer to take a look at that and tell you if it is safe to do that. You can't just add a lot of extra weight on those joists unless it is safe to do so. Those joists are very small, and they span a long distance, so they won't be able to handle much extra load. You might need to replace them with something bigger. A structural engineer is the only persona qualified to tell you.
Because i live in Norway, we don't have access to the RC1 Channel, since i am going for a double frame wall it does not apply to the walls.
Once again, you do NOT need a double-framed wall! You only need ONE frame in there, a few cm away from the existing concrete wall: Then you put drywall ("gypsum board") on only ONE side of that frame. Done!
But for the celling i need some kind of decoupling, so.. what we have on offer up here in the fjords is this:
That does not look like it will decouple much, but even if it does, you won't be able to do that. Your ceiling joists will not be able to support all of that extra load. It wont be able to handle the load of the two layers that you need to "beef up" the floor above you, and also the two layers that you'd need for the ceiling itself, and also the joists, and also the acoustic treatment that you will need on the ceiling, and also the insulation that you will in the cavity, and also the lights, and also.... There's just too much load up there.
The only option you have here is to put new joists across the top of your new walls, and put your new ceiling on those joists.
The file is now to big to upload to this site, so i'am using dropbox!
But you still have two frames in there! There is NO NEED to have two frames around your room! One of them is doing NOTHING AT ALL! You only need ONE single frame there, with drywall on only one side of it. You are wasting a lot of money, time and effort by building that frame which does nothing...
And it's far from symmetrical to say the least.
It's still fine. You can have the control room area in the narrower end of the room, facing the walls, and you will have good symmetry there, then you can have your "recording" area at the other end, where it is wider. That would work out fine.
Reading through Rod's book again, and i just realised that i should add 2 layers of drywall on the outside of the first assembly, how else would i achieve an airtight construction?
I think you are misunderstanding the concept here! Your existing concrete walls ARE your outer leaf. So no you ONLY need to add the INNER leaf. If the concrete walls do not complete surround your room, then you might need to build an isolation wall in that area to complete the outer leaf, but for those parts of your studio that will be directly facing the existing concrete walls, that is all you need.
My biggest fear is to be half way through the construction end then suddenly understand that my assembly will not work. I'll rather spend 6 months planing this to perfection,
Exactly! That's the smart, intelligent, correct way to design a studio. Do it all in SketchUp, and double-check everything, to make sure it all fits properly, and nothing gets in the way of anything else.
However, I see one big problem with your design so far: there is no HVAC! You definitely will need both ventilation and air conditioning in that room, and HVAC takes up a lot of space. You should start planning for that now as well. It is very important....
- Stuart -
