Drywall is nailed to the bottom edges of those truss members, thus creating the "middle" leaf of the three-leaf MSMSM system. The walls are normal 2-leaf MSM walls, but the ceiling is 3-leaf, with that middle leaf effectively completing the outer "shell" of the isolation system. Actually, it wasn't just drywall in this case: first a layer of plywood went up, directly on the bottom of the truss members, then two layers of drywall were nailed onto that, with Green Glue CLD compound in between. Like this:
V2-S055-middle-ceiling.jpg
That's from part of the original design concept, viewed from above, looking down on the roof as if there were no roof deck. You can see the plywood on the bottom of the trusses, and the drywall below that.
I couldn't find many photos of the completed middle-leaf ceiling, but here's one taken later in the build, where you can just see part of it right at the top edge. All of the framing and OSB you see there is actually the inner-leaf of the control room, partly built. That photo is taken roughly from the mix position, looking towards the back of the room, and you can see a bit of the middle-leaf ceiling above that, at the top edge of the photo.
OWCAUS--CR-inner-rear-+-middle-leaf-ceiling.jpg
Here's some photos from a different studio I did a while back, much larger than the one above. Same concept:
First, just the trusses in place, before the roof went on:
FRKCAUS--01--Roof-trusses-open-SML-ENH.jpg
Then with the roof completed and the trusses still exposed:
FRKCAUS--02--Roof-trusses-done--SML-ENH.jpg
Then with the first layer of sheathing on (OSB in this case):
FRKCAUS--03--Roof-trusses-sheathed-SML-ENH.jpg
And finally completed, with the drywall on as well (and part of the inner-leaf wall being raised):
FRKCAUS--04--Roof-trusses-sheathed-and-drywalled--SML.jpg
It should be clear form the above that the middle-leaf ceiling on the bottom of the trusses completes the shell, and then you build your individual rooms inside that shell, each as it's own single-leaf structure that does not touch any of that outer shell at all.
In other words, each room is built as a separate, stand-alone frame, consisting of the walls AND the ceiling for that room, with drywall on only one side of that framing. Each room is fully independent, has its own walls and it's own ceiling, does not touch the outer-leaf walls or middle-leaf ceiling at any point, and does not touch any other room.
This is what I was looking for! I need to find a structural engineer who can help design this for my building.
Actually, it's your studio designer who should design that part! It's an acoustic system, so the studio designer should do it. Then the structural engineer should check it, make sure it is safe, make sure it meets code, etc. Then the architect should draw up the plans for presenting to the relevant authorities, along with the structural engineer's signed report. Then once that is approved, you can hand it all over to the contractor, who will actually build it.
You seem to be confusing the issues here:
ONLY the designer should do the actual design for the complete studio, and that design should include everything: all of the walls, doors, windows, ceilings, floors, the HVAC system, the electrical system, and everything else that is even vaguely related to isolation or acoustics. That's what the designer does. Not the architect, not the engineer, not the contractor. Once the design is complete, in every aspect, it goes to the architect and engineer, who check the structural and code compliance aspects, and create the drawings. In your case, the design will also need to go to the HVAC contractor, so he can check the calculations (flow rates, flow speeds, static pressure, sensible heat load, latent heat load, climate conditions, AHU, HRV (if there is one), etc.) and make sure it will all work. And it will also need to go to the electrical contractor for checking, and also the plumbing contractor. All of them need to see the design, and make sure that there are are no issues with it, then it goes to the architect and engineer. There's a whole process here. I'm surprised that either your general contractor or your studio designer didn't mention this in the initial meetings you had with them. That's part of their job! to coordinate the build. Perhaps your GC does not have much experience with recording studios? Or maybe your studio designer isn't too familiar with the actual build process? Either way, I'm sensing some little red flags here, waving warnings about future issues with your build.... not necessarily technical issues, but coordination and work duplication issues...
At the risk of overkill, let me clarify again: It is the job of the studio designer to do the ENTIRE design of the complete building, including
all aspects. The contractor is NOT involved in this. Neither is the architect, engineer, or anyone else. The designer will probably be talking to them along the way, but it's the
DESIGNER'S gig. Once the initial design is complete, it goes to the architect and structural engineer, who will check for safety, structural issues, code compliance, etc. The architect then draws up the plans, and those go to the electrical guy, HVAC guy, framer, plumber, etc. for comment and suggestions. The drawings then need to go back the designer for double checking, to make sure nobody screwed up the acoustics with the modifications, and when all issues have been dealt with, the drawings and other documentation go to your relevant local authorities for their rubber stamps and permits. Only then do the contractors get to start work.
The studio designer is the central hub of the process, simply because the entire purpose of the project is to have a
studio! And since studios are nothing at all like normal construction, the designer will also need to be "looking over the shoulders" of the various contractors during the build, to make sure they really are following the design, and not cutting corners or screwing up in other ways. Nobody else on the team understands acoustics, so nobody else will be able to determine if things are being done right. It doesn't take much to totally trash the isolation of a studio: one gap that wasn't sealed properly, or a nail in the wrong place, or a wrong wall penetration, will all cost you dearly. Typical contractors don't know or care about that, because it isn't important when they build a normal house, shop, office, school, etc. But it is critical for a studio.
Hopefully you already knew all of that, but it doesn't hurt to check!
- Stuart -
