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Example from Roxul: insulating a home theatre room

I like this video from Roxul because the presenter clearly explains the difference between the two types of noise: airborne and low-frequency noise, which I will add to here.

The lower frequencies travel through the wood studs. A low frequency travels from your wall surfaces, floors, and ceilings if they sit directly on those studs. Lower frequencies include bass from your stereo, impact sounds from walking or pounding, trucks driving outside, and maybe the spin cycle on a washer.

Roxul insulation mitigates the other kind of noise -- airborne noise -- which can include talking and TV (without bass). This insulation product is dense and does a really great job of blocking airborne noise. However, used alone, it doesn't stop low-frequency noise.

The presenter shows how to insert Roxul batts between the studs, which you've seen before. Then he installs a resilient channel to keep the drywall from touching the wood studs. The resilient channel's job is to reduce the low frequencies that might get passed into the wood framing.

The first layer of wall is installed horizontally. Then he installs a second layer of drywall on top of the first layer, and this time he installs the drywall vertically, so the seams of the second layer don't overlap the seams of the first layer.

I think everything in his process is really solid, but I would have done one more thing: I would have also applied some Green Glue to the second layer of drywall before I installed it. Or I would have used a soundproof drywall (like QuietRock) for at least one of those layers of drywall.

If this is a remodel, it already will be superior to the previous construction and it will reduce the noise coming into and out of that room. However, I think there's a missed opportunity here: if he'd applied Green Glue between the two layers of drywall, it could absorb some of those low frequencies before they even get to the resilient channel.


  1. Great blog! Here's a question: In sound-insulating an existing floor/ceiling, should I (1) blow in cellulose, or (2) add Green glue and an additional layer of sheet rock? Or do I need to do both?

    This is a simple construction, recently renovated, with drywall ceilings below wood joists, then plywood and wood floors on top of that. No insulation. Right now conversations/TV at normal volume and footsteps are coming through.

    I don't need perfect soundproofing but need a bit more sound protection than we've got currently. Thanks for any help you can offer.

    1. Blowing in cellulose definitely helps to mute conversation noise. It won't mute footsteps or any impact noise. I have no personal experience with adding an extra layer of drywall to a ceiling with Green Glue (only to walls), so I don't know how effective it is. I've seen reviews on the internet from people who say it's less effective on ceilings than on floors, and they advocate a drop ceiling with additional drywall, which is fairly effective.

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