Two great products work great together.As I've mentioned before, I'm experimenting around with ways to reduce some of the noise problems in my apartment on a tight budget. I think I've found the best combination to date: adding a layer of QuietRock 510 over an existing layer of gypsum drywall with a layer of Green Glue inbetween.
This was sort of the best of both worlds: taking a pre-made, sound-dampened drywall and then adding it over a powerful, viscous layer of glue....onto drywall that was already on the wall studs. No demo needed. In this project, I basically added two sound-dampening layers to the original 1950s drywall (one layer in the QuietRock and the other layer created by the Green Glue) to address "flanking noise": feet, furniture, and shoes pounding on the bare floor of my downstairs neighbors' apartment. The amount of banging, bashing, and foot-stomping sounds coming from their very "wooden" apartment has been severe, and I've had a hard time finding information about how to deal with noise that comes from below. Most sound solutions are for people who live underneath noisy upstairs neighbors, while I have the opposite issue.
I found the results very effective. The walls feel as solid as concrete, and the impact noise from my neighbors has been reduced to coming through my floor joists and not through my wall studs. It also muted the sound of their closet door rolling open and shut beneath me. (I still want to solve the floor problem.) The entire room now has Quiet Rock walls in it: two of the walls have a single layer of QuietRock 525 (the 5/8" QuietRock that has a concrete-like layer on it), while the other two walls now have double drywall, with the top layers comprised of QuietRock 510 and Green Glue.
How to buy what you needI ordered the Green Glue online by the tube from Super Soundproofing, and bought the QuietRock locally (in San Francisco, at SF Gravel Company at Berry and King Streets -- note that in 2018, this company no longer exists). You can also call QuietSolution to find out who sells QuietRock drywall in your area.
The cost was relatively low: the sheets of QuietRock were less than $50 apiece, the Green Glue was about $17 per tube (I didn't have to buy an entire case of it), and the process of adding the additional wall, caulking, and mudding over it was less than if I had demolished the existing wall and started over.
What to expectI've made a short video here to show the difference between the original wall, then the new wall two days later, and again two weeks later. I've read that Green Glue takes 3-4 weeks to "cure," so its dampening powers could potentially improve even more. Highly recommended, and in my opinion, more effective than just screwing QuietRock onto your wall studs.
Some people have commented that it seems like I wasn't knocking hard enough on the QuietRock wall to show the difference. I dug up a few other bits of video that hopefully shows more convincing knocks.
Update in 2021: I've made a video that shows measurable results for this room and how it performed during a very loud, external street-construction project. I measured the noise in the QuietRock room and compared it to the decibel levels in the un-soundproofed room. Here's the story: