Double 5/8" Drywall vs QuietRock and Doors and inwall speakers - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 11 Old 12-29-2009, 06:36 AM - Thread Starter
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Hi all,

So from what I gather, double 5/8" drywall will outperform soundproofing drywall like QuietRock?

This seems to be good news considering 5/8" thick drwall is much cheaper

With double drywall, how do you hang doors, junction boxes, etc? Won't the drywall be so thick that it's difficult to mount some of this stuff?

Also, what about inwall speakers? Most only mount onto drywall ~5/8" thick? I understand with inwalls I'll be scraficing the sound dampening qualities of double drywall, but I do like the clean lines of inwall speakers.

Thanks for answering these questions, I'm still in the very early stages of planning a home theater ... afterall I just bought a house <6 months ago!
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post #2 of 11 Old 12-29-2009, 06:53 AM
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Quote:
Originally Posted by mshe View Post


So from what I gather, double 5/8" drywall will outperform soundproofing drywall like QuietRock?

Yes if damped. More mass alone is a big reason. Double 5/8" rock is not only cheaper, but much heavier.

With double drywall, how do you hang doors, junction boxes, etc? Won't the drywall be so thick that it's difficult to mount some of this stuff?

Just plan around it. Outlets have extenders, and doors can have the jambs cut to accomodate any wall depth.

Also, what about inwall speakers? Most only mount onto drywall ~5/8" thick? I understand with inwalls I'll be scraficing the sound dampening qualities of double drywall, but I do like the clean lines of inwall speakers.

This will seriously compromise your sound isolation. You're pumping sound straight into the stud cavities and into the original framing.

The alternative for in-walls is to build massive backer boxes, but still not desirable from a pure sound isolation perspective.

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post #3 of 11 Old 12-29-2009, 07:21 AM
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re: outlets, I've heard suggestions to use old work boxes. Sounds like an easy alternative but how do you seal them? Seems no way to use putty pads or backer boxes with old work junction boxes.
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post #4 of 11 Old 12-29-2009, 07:23 AM
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You can line the interior of the box with a fire-rated Putty Pad.

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post #5 of 11 Old 12-29-2009, 08:03 AM
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I will be using in-walls for my surrounds but, I'm going to incorporate them into decorative columns. The same holds true for electrical outlets and sconces.
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post #6 of 11 Old 12-29-2009, 08:07 AM
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What a great way around the issue.

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post #7 of 11 Old 12-30-2009, 05:01 AM
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Well, the lab data is quite clear that a damped wall using QuietRock will outperform not only 2 layers of drywall on both sides, but 3 and 4 as well.
A 24OC wood stud wall with 2 layers of 5/8" drywall on both sides has an STC of 44 (up from STC of 39 with a single layer of 5/8").
QuietRock on both sides has an STC rating of 52 to 60, depending on the model (there are many to choose from). Even at lower frequencies, QuietRock outperforms double drywall easily. All these tests are 3rd party and readily accessible. All referenced in this document:
http://www.quietsolution.com/acousticfireassemblies.pdf

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post #8 of 11 Old 12-30-2009, 05:06 AM
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Quote:
Originally Posted by Kevin Surace View Post

Well, the lab data is quite clear that a damped wall using QuietRock will outperform not only 2 layers of drywall on both sides, but 3 and 4 as well.
A 24OC wood stud wall with 2 layers of 5/8" drywall on both sides has an STC of 44 (up from STC of 39 with a single layer of 5/8").
QuietRock on both sides has an STC rating of 52 to 60, depending on the model (there are many to choose from). Even at lower frequencies, QuietRock outperforms double drywall easily. All these tests are 3rd party and readily accessible. All referenced in this document:
http://www.quietsolution.com/acousticfireassemblies.pdf

cheers,
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Green Glue would be going between the layers of drywall, so, QuietRock will still outperform? I don't think so. QuietRock also costs far more.
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post #9 of 11 Old 12-30-2009, 06:36 AM
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As for the outlet boxes, this is your best bet:



They have a screw adjustment that lets you move the box in and out after it's installed.
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post #10 of 11 Old 12-30-2009, 07:44 AM
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I have not seen many claims that double drywall (even with green glue) "outperforms" QR545. Even Ted has stated many times that the double drywall approach will not match or outperform QR545, especially in the lower frequencies. I think he may have a different view once you get to 3 or 4 drywall layers with green glue, but I don't want to get into that debate because I have nothing useful to add.

For many it is simply a cost/benefit analysis and ease of install issue. I was going to use QR545 and instead did three layers of drywall with green glue. I am very happy with the results, but certainly would have expected the 545 to perform as well or better. I just decided to use the cost savings to fund other parts of the room. I realize I may have given up some level (especially lower frequency) of sound control.

I would recommend either (green glue approach or QR545), but would caution that based on my own research the 545 needs to be carefully installed to avoid gaps etc. With the multiple drywall approach you get to cover up your mistakes.

If you can go with the QR545, I suspect you will be very happy with the results. For me, the three layers of drywall with green glue was a great solution.
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post #11 of 11 Old 12-30-2009, 08:09 AM
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Quote:
Originally Posted by Dixon View Post

I was going to use QR545 and instead did three layers of drywall with green glue. I am very happy with the results, but certainly would have expected the 545 to perform as well or better. I just decided to use the cost savings to fund other parts of the room. I realize I may have given up some level (especially lower frequency) of sound control.

Not sure you gave up anything, Dixon.

The Quiet products are excellent and I have always admired the bona fide testing. Too bad other companies / products don't test as thoroughly.

I would offer that similar pre-damped panels from Temple-Inland (ComfortGuard), National Gypsum (SoundBreak) and Supress also work very well and are also independently tested.

When we peel away the variables and look at the basics, the performance answer comes down to mass and damping.

Three sheets of 5/8" rock would weigh 205-210 lbs perhaps. Two layers of damping means a thoroughly damped laminated panel system.

One sheet of QR545 weighs 205 lbs (essentially the same) and is also thoroughly damped.

Both situations perfectly installed with no flanking would provide excellent overall isolation, including in the low frequencies.

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