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Upgrading existing walls

You can add mass to your existing walls.

As I mentioned in a previous entry, I successfully muted some neighbor noise in my apartment building when I added a second layer of drywall on top of the original 1/2" drywall, with a coating of Green Glue in-between. This produced better results than simply replacing the original wall with QuietRock 525. I made the double-drywall solution even more successful by using QuietRock 510 as the second layer of drywall, with Green Glue in-between the two.

Here's a diagram from Trademark Soundproofing that demonstrates the STC results between different wall assemblies, including those with Green Glue. 

Why do I think the Green Glue + layer of QuietRock was better than just replacing the original wall with QuietRock, right on the studs? My theory is that when you add QuietRock directly onto the wood framing, you're still not decoupling it from the structure. And therefore, impact noise and lower frequencies might still come through, even though conversation and other frequencies of noise might be reduced. However, by adding a second layer of drywall on top of a viscous layer of Green Glue, some of the impact noise from the framing might not resonate through the layer of Green Glue to the layer of new drywall -- at least not to my ears. And any gaps in coverage of the Green Glue between the two drywall layers will also be mitigated by the layer of dampening material that's already inside the QuietRock drywall.

Of course, sound travels in many different ways -- not just through the walls. Here's a quick primer from Trademark Soundproofing in the "5 Principles of Soundproofing."



    Damping and decoupling are often confused or used interchangeably. They are, in fact, separate functions.

    Examples of decoupling would be the use of resilient channel, resilient clips + channel, staggered studs, and double stud construction. This is a physical disconnection of the drywall on one side of a wall from the other. Or the ceiling drywall from the wood floor above.

    Damping is the conversion of the kinetic energy travelling through a panel to thermal energy. Vibration to heat. This process robs the system of vibrational energy, therefore less is left to exit the board as sound again.

  2. Yes, thanks for clarifying. What I was really talking about here was workarounds that successfully dampen sound when you can't decouple from the structure, for one reason or another.

    From my own experience, I tried QuietRock 525 first. I removed two walls and insulated with fiberglass batts, then put the new walls directly onto the studs. I believed that this was all I needed, and the literature implies that this is all you need to do to block noise economically. The new walls do block most airborne noise, but I discovered that I was still getting impact noise.

    One of those new walls faces an adjacent apartment building, and someone in that building does a lot of mysterious slamming, which transmits into my room....presumably through the QuietRock as well as other pathways. I can also still hear some impact noise that comes from the bare wood floor in the apartment that's below me, but this might be coming through my floor, which is also not decoupled from the structure.

    For the other two walls in that same room, I tried a different approach: I added a second layer of wall on top of the first one -- but with a layer of Green Glue inbetween. I didn't demo the original wall --it's still attached to the studs. So two of my walls are 1" thick, with a layer of Green Glue in the middle, and the outer layer made of QuietRock 510. The other two walls are 5/8" thick, comprised only of one layer of QuietRock 525.

    With the combination of Green Glue and QuietRock 510 (the slightly thinner, less-expensive QuietRock), I got both mass + dampening, and it seems to also absorb some of the impact noise, not just the airborne noise.

    Now the question is whether or not Green Glue would successfully dampen the impact noise that's coming from the apartment below me if I put it on top of my subfloor and made a subfloor "sandwich"....


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