you are saying the MSM thing won't work, when I have mass (gypsum) - wool - mass - wool - mass?
Correct, because that would not be MSM: that would be MSMSM. That's a three-leaf wall, which will always isolate WORSE than the equivalent two-leaf wall, all other factors being equal.
So, I'd rather need mass (more) - wool (more) - mass (again, more)?
Yes. That's MSM.
Afterwards, I use the same principle on the other side. My wall would look like this:
That's one way of doing it, if you have access to both sides of the wall. Brian is suggesting another way of doing things, which is very useful if you only have access to one side of the wall.
2) I assumed that two layers of 14 mm gypsum (these are the ones I already bought) add up together as one 28 mm mass. Or not?
Not!
Well, OK, let's say "yes and no": Sure the total mass is the sum of the two individual masses, but that's not the only issue here. It's a bit more complex than that. Two sheets of thin drywall do not act the same as one sheet of thick drywall, since the panel has properties other than just pure mass: thickness, rigidity, flexibility, resonant frequency, coincidence dip, etc. All of those change for different thicknesses of panel. So, for example, if there were such things, then two sheets of 8mm drywall would NOT work out the same as a single sheet of 16 mm drywall. The wall made with two sheets of 8mm would not isolate as well as the wall made from the single sheet of 16mm.
I suppose that green glue is to join these boards even tighter, right?
Nope! As Brian pointed out, is not really glue at all. That's just the name of the product, but does not describe what it does. Maybe they could have chosen a better name!
What it does is not to glue the sheets together, but the exact opposite: it keeps them apart! It creates a thin layer of rubbery "stuff" with tiny air gaps in it, which acts to damp certain types of resonance in the wall, and that increases the isolation.
Regarding the glue - it looks expensive:
Yup! But you might not need it: how much isolation do you need?
3) Regarding the fibreglass: That guy who is going to inject my ceiling with stone wool could also do that with the wool.
Brian already mentioned this, but I'll repeat it: blowing in insulation is not a good way of isolating walls, acoustically. You run the risk of creating both flanking paths and voids, and also of uneven distribution in the cavity. All of those are Bad Things That Should Be Avoided.
but packed tighter than with doing it bay hand. Do I understand you right that looser is better in that case?
Correct: you do not want it packed tight at all! You want it loose. Just enough insulation to fill the cavity, and no more. You should NEVER pack insulation tightly if you need isolation.
4) Regarding airtight: When I plaster each drywall separately, is that air tight, or are additional treatments needed.
Yes, more is needed: you need to seal the framing to the floor with acoustic sealant, at least 3 seals (five is better). Same where walls meet: the frames must be sealed together. Same where the walls meet the ceiling: acoustic sealant in the gap. Very important. Sealing is critical to isolation You need two perfect, hermetic seals: one for the outer leaf, one for the inner leaf.
Also, to decouple the ceilings above each room, I had to cut the ceiling open. So, the Air inside the wall will always be coupled to the air inside the ceiling, even if I manage to get the wall tight. Is that a problem?
If I understand you right, that is fine: But do you mean that the air between the inner-leaf ceiling and outer-leaf ceiling meets the air between the inner-leaf walls and outer-leaf walls?
I do not expect to isolate a rock drummer ... I think this would require a room in room construction;
Ummmm..... don't look now, but everything we are talking about so far IS for room-in-a-room construction!
That's exactly what you are doing.
I slightly angled the wall because I had read that to be a good thing somewhere.
Well, yes it is a good thing, but you angled the wrong wall! For a control room, the rear wall should be parallel to the front wall, or at least symmetrically non-parallel, if possible, oar worst case, designed specifically to not reflect sound back to the engineers ears too soon or at too high a level.
the wooden frame of the wall rests on a footfall absorbing rubber layer - about 1,5 cm thick; I bought the pieces they sell for putting your drum set on it; meanwhile, I found out it might be to hard or to soft - I should have calculated the weight of the wall
Unless you did all the calculations, then the chances are pretty close to zero that it is not doing anything useful. For example, what is the total mass of that wall, including everything that the wall supports? And what
deflection are you getting on the rubber under that load? And what deflection does the manufacturer of that rubber recommend for optimum float? If you didn't figure that out carefully, then I suspect that you just have an expensive but useless decoration under your wall...
but I already started building that wall frame, so I would only redo that if it really matters a lot; what do you think?
How did you attach that wall to the floor underneath? Did you use bolts, screws, nails or something else?
- at both sides the wood frame is drilled into the concrete wall with massive screws; I suppose I can ignore the transfer, as the walls are massive and the whole studio is in the basement, hence, connected to ground soil; am I right with that?
Actually, it is the other way around: If that wall is firmly attached to the side walls, then
nothing is decoupled, and sound will transfer very well between rooms. Sorry.
the guy who is going to inject the ceiling with rock wool told me, he could also fill my wall with it; it is going to be much denser, than I could achieve by doing it with fiberglass pieces; the question here is: denser better or not?
What do you mean by "dense"? Put that in numbers. And what type of insulation? There is an optimum density for each type of insulation. denser is not better.
5) About the decoupling the new frame: Is the drummers mat on the floor going to do the job? Does the drilling to the side walls cause a problem? If so, how else do I get the required stability?
One at a time: "Is the drummers mat on the floor going to do the job?" No. "Does the drilling to the side walls cause a problem?" Yes. "If so, how else do I get the required stability?" You decouple the walls, by building a complete "room in a room". You CANNOT isolate two rooms unless you decouple everything: Just building a wall between them will NOT achieve good isolation, unless you also cut all the flanking paths. And the only way to do that, is to build the room correctly, as four decoupled walls with a decoupled ceiling on top.
6) Finally, what do you suggest regarding the framework in the ceiling? Do I have to uncouple (cut) that between the two rooms?
Yes, but you have to do it correctly!
- Stuart -
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