The span is a little less than 11'-0". About 10'-8". I believe the number I came up with was around 13psf for the load
OK, that sounds about right. It looked like a longer span in the photos. Optical illusion, I guess.
Independently?
Right. The layers of a leaf act both together, as a single mass, and also independently.
I don't think I am following? Did I do ALL MY WALLS WRONG TOO? I screwed the gypsum to the OSB? they are 100% directly fastened to eachother rigidly.
You should only use screws (or nails) into the STUDS (or joists). Yes, the screws on the drywall will also go through the OSB, then into the studs, but you don't ever screw only into the OSB where there is no stud behind. If you screwed the drywall into the OSB away from the studs, then that's not so good. It's the same as gluing the layers together.
Screwing or gluing two panels solidly together will make them act as one, with one single coincidence dip frequency taht will be LOWER than the individual coincidence dips for each panel by itself, and the bend/flex characteristics will also be different from having the panels separate. In almost all cases, this is not good for sound attenuation. When the panels are only attached to the studs, with broad open areas between them, even though the faces are in contact they can still move independently, with the layers sort of "sliding past" each other if necessary, especially with the case of bending waves, but also with plain old flexing waves. To understand with a simple practical illustration: pick up any paperback book that you happen to have on hand, and firmly grip the spine in one hand and the opposite edge in the other hand, pressing the pages together tightly. Now bend the entire book, so that the front bends towards you, then away from you, then towards you again. Not what happens to the pages in the middle of the book: they slide past each other as the "flexing wave" moves through the book. In effect, that's what happens to the layers in a leaf on the wall as sound waves cause it to flex, just on a smaller scale. The friction between layers adds to the isolation, since it removes some of the flexing and bending energy. And that's what Green Glue helps with: it damps that "sliding" action, since it is viscous, so it removes even more of the energy than friction alone would. But if you rigidly attach the layers to each other with screws out in the "field" of the sheathing, then that action cannot happen, and the two layers act more like a single, solid, rigid block, with a lower coincidence dip. This is the same reason why windows should be laminated glass, which is two thinner panes of glass with a flexible PVB bonding layer between them. That allows the two panes to flex and bend independently, as well as together, and the interlayer absorbs some of the flexing/bending energy. That's why laminate glass has superior isolation to what you'd get from a single solid glass pane of the same thickness.
I did NOT use green glue. Is green glue REQIURED?
No, it's not required. Not at all. It helps, yes, since it puts a damper on several types of resonance that happen in the wall sheathing, but it is not NECESSARY to get good isolation from a wall. It's just an extra boost for low frequency isolation. It works, yes, but it's expensive. So it's a cost/benefit thing: If you absolutely must have the best possible low frequency isolation, then it is worthwhile using Green Glue. But if you don't absolutely need that extra boost, and can't afford the extra cost, then that's OK. The wall won't isolate quite as well as it would have WITH the Green Glue, but it also won't be terrible! You can get roughly the same boost as Green Glue would give you, by simply adding one more layer of drywall.
So basically: It's nice to have if you can afford it and can justify the cost, but is not required. Not by any means.
Why can I not have the gypsum screwed into the osb? I though the whole point was to make a massive leaf?
Yes, you certainly do need the mass! But mass is only one aspect of how walls isolate. There are four main aspects: Mass, spring, resilience, and damping. And there are five regions of the spectrum where each of those has a different role, with some being dominant in one area and others dominant in other area. For frequencies BELOW the MSM resonance of the wall, resilience rules. Down that low, it is the key aspect. The walls "breath", like a balloon inflating and deflating, in sympathy with the sound pressure. You want the wall to be flexible and resilient but also damped for very those low frequencies, since that's the major mechanism that is removing energy from the waves. Around MSM resonance, mass, spring and damping matter most, with resilience being less important. Between MSM and coincidence, mass matters most (although the others do still play a role: just reduced). At coincidence, we get back to resilience and damping. Above coincidence, it's mostly mass again. There's a LOT going on in a wall to get you good isolation at all frequencies. Imagine how hard that wall is working when you have a deep sub-sonic thump from the kick, plus the bass guitar doing things around MSM, the keboards fleshing out the middle, the electric guitar smashing into coincidence, and the cymbals screeching through the top end... all at once! The wall is doing all sorts of stuff together to isolate all that, and of course, there's also interaction between them: the ultra-low flexing of the wall has the bending wave from the bass riding on it, with the mids and highs superimposed on that... so each panel of the wall is vibrating in several different modes at the same time... It gets complex!
I've been on here for 3 years and I dont even know how to build a wall!
It's not that bad! You have built them quite well... maybe not optimally, but certainly not bad!
I thought the reason I used cleats for the "beef-up" was so that I didn't risk putting a nail through the sub-floor or pushing up any floor finishes above?
Not really: it's mostly to keep the panels acting separately. If it weren't for that, you could just use shorter screws...
I just want to know if I missed something major and I'm doing all my walls wrong too?
I'm not 100% clear on how you did those: if you ONLY put screws through the drywall where the studs are, then that's great! But if you ALSO put ADDITINAL screws through the drywall and into the OSB at locations where there are NO studs behind, then that might be a problem... The magnitude of that potential problem is hard to predict...
Ok yes 10% is a significant amount, I guess I was thinking the MSM system had more to do with Volume of the cavity.
Actually, not really! there's no parameter in the MSM equations for volume. Only for depth. There's only three variables that you can change in the equation: the mass of the leaves, the distance between them (depth of the cavity), and the damping factor (given by the insulation). The volume of the cavity does not come into it, for MSM. Here's the actual equation:
f0 = C [ (m1 + m2) / (m1 x m2 x d)]^0.5
Where:
C=constant (60 if the cavity is empty, 43 if you fill it with suitable insulation)
m1=mass of first leaf (kg/m^2)
m2 mass of second leaf (kg/m^2)
d=depth of cavity (m)
That's it. No volume.
but when you look at the cubic volume of the overhead cavity, we are talking like less than 1%?
Right, but not relevant!
Just a visual glance at one of the bays you can see that it's about 99% filled, not 90% filled.
And that's a good thing! But that is "damping factor" in the equation, not "cavity depth"...
Either way, this point makes a lot of sense so I think I will be increasing the gap in the control room.
One way you could do that is to simple drop the "modules" down an inch. Instead of having the bottom face of your module flush with the bottom of the joists, they would be an inch lower. That still gives you an inch and a half of contact between module frame sides and the joists, which is fine. Yeah, that means the bottom edge would be an inch lower, which might not be so pretty... but I'm assuming you'll be covering those modules with fabric of some type, so you could just paint the bottom face of the joists black, and that can look nice up there.
As far as the reduced isolation I'm starting to lose track of all the many many many places where I have settled for (slight loss in isolation) over and over again. Single doors, less MSM distance than I would have liked, AC openings, electrical conduits, no green glue...... I'm wondering if I'll have any isolation at all once these slight losses add up to a big loss in isolation
How much isolation are you shooting for? What's your "number"? (in decibels) If you really suspect that you aren't going to get there, then you can always add another layer of drywall to all of your inner leaf. If you do that on your ceiling you should re-check with your engineer, but from what you said above, there seems to be enough margin to handle the extra load (the walls are not a problem from that point of view).
There are solutions...
- Stuart -
. Then once you get into door openings with 2x6 headers below the double top plate, you basically have a door that you have to crawl through to get into the room. I had to choose lesser of two evils here. 
