I've read up on sound isolation techniques, and I understand the physics behind sound damping with products like Green Glue, which essentially converts sound energy to heat when it flexes, thereby reducing the energy in the vibration. It's easy to see how a room with all surfaces damped would do a good job containing the sound. But when installing the damping material and drywall against the subfloor, between the joists, the joists themselves are left as sound transfer paths. There will also inevitably be gaps between the drywall and joists, as well. BUT, if I understand the contribution of the Green Glue correctly, it doesn't HAVE to be a continuous, unbroken surface for the job it is doing. For example, sound entering the joists will transfer to the subfloor above, but the damping material against the subfloor in the surrounding area will still absorb and convert some of that sound energy to heat. The same goes for sound entering the subfloor in the gaps. Now, obviously it would be better to dissipate the sound BEFORE it reaches the subfloor, but the real question is HOW MUCH of a difference can actually be heard between the continuous surface scenario and the non-continuous surface scenario?
Edit: Copied from my post below. Clarifies my question.
To clarify my question, consider this video
, which demonstrates the effect of Green Glue "sandwiched" between two ceramic tiles versus conventional adhesive. When striking the tile sandwich with Green Glue using a hard object, the resulting sound is significantly quieter than when striking the tile sandwich with conventional adhesive. Now imagine cutting a strip, about 1/5th the width of the tile, out of the middle of one of the tiles with Green Glue, then performing the test again, striking the tiles in different places, on both sides. This is obviously an experiment I could do myself, and perhaps I will, but I know Green Glue takes about 45 days or more to fully cure, and I can't really wait that long to move forward. Regardless, as I said, I also want to start a discussion about how Green Glue works in this type of application. My prediction would be that the sound would still be significantly dampened, regardless of where you strike the tile. I would think that only the amount of surface area near the source of the vibration that has Green Glue between tile would determine how much damping occurs. So in the drywall under subfloor scenario, I would think that the damping effect of the Green Glue would be essentially the ratio of (drywall and Green Glue covered surface area) / (total floor surface area).