for my first layer of drywall on my outer leaf, I simply screw it to the studs like any other job, right (no adhesives, cleats, etc.)?
...and once that layer is up, ideally, I'll then Green Glue the next layer of drywall to the first (w/seams staggered), and again, screw through the first layer of drywall and into the studs, just like I did with the first layer, but with Green Glue this time, correct?
Exactly! Yes, that is indeed, the correct way to use Green Glue.
The question that eludes my understanding here is weather or not the green glue will actually offer any extra benefit,
Most definitely! See their website and the rather large section of technical testing they have had done on walls built with their product, at independent acoustic testing labs. It is quite well documented.
since the two layers won't act independent of one another;
Why not? I don't understand your doubt here. You have two layers of drywall, separated by a visco-elastic polymer: why are you concerned that this could prevent them from acting independently? That's actually the point here: they layers
do still act independently, and
are able to flex and slide past each other as the waves cause the surfaces to vibrate in different manners. The Green Glue compound acts on that independent movement, damping it, as well as damping other vibrations that involve both surfaces together. If you were to use construction glue, for example, or any other type of glue other than Green Glue, then the layers would NOT be able to act independently, and that's a different acoustic scenario. In that case, they would act as one single, solid mass, and therefore the coincidence dip would move down to a lower frequency.
I do recognize the value of the GG's low frequency heat dissipation characteristics, and I imagine that is the main, if not only, real world benefit here?
... and it achieves that precisely BECAUSE the two layers remain independent! That's how constrained layer damping works! You have a
damping material that is
constrained between two
layers of building materials, that are otherwise free to vibrate independently. The relative motion between those two layers is damped by the CLD, and converted into low grade heat. That's how CLD's work. But this is not just a low-frequency issue: it also works at higher frequencies. For example, at the coincidence dip, where the bending wave is causing both layers to follow the same vibratory motion as a single unit, the motion of that wave across the surface of the leaf still causes some relative motion between the layers (thin about it....), and the CLD still acts to damp that. Thus, a wall with GG shows improvement in isolation at low frequencies as well as in the mid range, where the coincidence dip occurs. And therefore, it improves overall isolation across the entire spectrum.
- Stuart -