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3rd Layer of Drywall - Green Glue or No?
Old 1 week ago
  #1
Here for the gear
 

3rd Layer of Drywall - Green Glue or No?

So in designing my drum rehearsal/practice studio, I am trying to achieve as much isolation as possible. 10 feet outside the room can get up to 115-120db. My inner leaf of a decoupled frame will be:

2x6 w/ 24 OC studs stuffed with R-19 insulation, 3/4" OSB, 5/8" drywall, Green glue, 5/8" drywall (all outer seems backer rod and caulked).

I currently have enough GG to use 3 tubes per sheet of drywall. My questions are if I want to go with another (3rd) layer of 5/8" drywall, should I...

1 - just add the 3rd layer to the wall, backer rod and seal it and be done.

2 - only use 2 tubes on the first drywall/GG/drywall sandwich, and purchase enough GG to apply 2 tubes to the 2nd drywall/GG/drywall sandwich...

3 - purchase enough green glue to use 3 tubes on the 2nd drywall/GG/drywall sandwich as well.

4 - do nothing, because the extra layer of drywall (either with GG or without) will not make enough of a difference to justify the cost?

Thanks in advance!
Old 1 week ago
  #2
Quote:
Originally Posted by Jag94 View Post
So in designing my drum rehearsal/practice studio, I am trying to achieve as much isolation as possible. 10 feet outside the room can get up to 115-120db. My inner leaf of a decoupled frame will be:

2x6 w/ 24 OC studs stuffed with R-19 insulation, 3/4" OSB, 5/8" drywall, Green glue, 5/8" drywall (all outer seems backer rod and caulked).

I currently have enough GG to use 3 tubes per sheet of drywall. My questions are if I want to go with another (3rd) layer of 5/8" drywall, should I...

1 - just add the 3rd layer to the wall, backer rod and seal it and be done.

2 - only use 2 tubes on the first drywall/GG/drywall sandwich, and purchase enough GG to apply 2 tubes to the 2nd drywall/GG/drywall sandwich...

3 - purchase enough green glue to use 3 tubes on the 2nd drywall/GG/drywall sandwich as well.

4 - do nothing, because the extra layer of drywall (either with GG or without) will not make enough of a difference to justify the cost?

Thanks in advance!
I found this interesting on the topic of Green Glue as explained by Dennis Foley of Acoustic Fields.

1.Acoustic Fields: https://www.youtube.com/watch?time_c...ature=emb_logo

2.Acoustic Fields: https://www.acousticfields.com/use-d...oom-acoustics/
Attached Thumbnails
3rd Layer of Drywall - Green Glue or No?-dennise-foley-acoustic-fields.png  

Last edited by Roll Tape; 1 week ago at 07:48 AM..
Old 1 week ago
  #3
Lives for gear
In general, you will get the best results with a mixture. The idea with glue, or anything, is to get air pockets between the sheets. change in mass helps too, even a layer of foil or plastic. Foam or metal would have a major impact.

for practical sake, I suggest two layers right on top of each other, than one air gap to the 3rd layer. Can be accomplished any way you want, would be simplest using trimming of sheet rock for a 4th layer---of space. One layer of plastic over the air gap will help things out. Could get fancy with the plastic layer over the air gap to keep crumblings out of the room.
Old 1 week ago
  #4
nms
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nms's Avatar
Quote:
Originally Posted by elegentdrum View Post
The idea with glue, or anything, is to get air pockets between the sheets. change in mass helps too, even a layer of foil or plastic. Foam or metal would have a major impact.
This is incorrect. Green Glue is a CLDM (constrained layer dampening material). It's purpose is to dampen.
Quote:
I suggest two layers right on top of each other, than one air gap to the 3rd layer. Can be accomplished any way you want, would be simplest using trimming of sheet rock for a 4th layer---of space. One layer of plastic over the air gap will help things out. Could get fancy with the plastic layer over the air gap to keep crumblings out of the room.
I would definitely recommend never offering any of this for advice again

Adding an additional air gap to such an assembly creates a 3rd leaf and resonant cavity. It is only helpful to increase the primary (single) air gap. So for example, increasing the main air gap from 7 to 9" is good. Building an assembly with a 7" cavity then drywall, then 2" air gap, then more drywall is bad. Don't do this. Just like you should never install resilient channel this way. You need to remove any existing drywall on the inner shell and mount it on the studs.

Quote:
Originally Posted by Jag94 View Post
My inner leaf of a decoupled frame will be:

2x6 w/ 24 OC studs stuffed with R-19 insulation, 3/4" OSB, 5/8" drywall, Green glue, 5/8" drywall (all outer seems backer rod and caulked).

I currently have enough GG to use 3 tubes per sheet of drywall. My questions are if I want to go with another (3rd) layer of 5/8" drywall, should I...

1 - just add the 3rd layer to the wall, backer rod and seal it and be done.

2 - only use 2 tubes on the first drywall/GG/drywall sandwich, and purchase enough GG to apply 2 tubes to the 2nd drywall/GG/drywall sandwich...

3 - purchase enough green glue to use 3 tubes on the 2nd drywall/GG/drywall sandwich as well.

4 - do nothing, because the extra layer of drywall (either with GG or without) will not make enough of a difference to justify the cost?
1 tube of GG will get you around 70% of the performance of two tubes. If you're going to use GG, just use 2 tubes/sheet.

Last edited by nms; 1 week ago at 04:42 PM..
Old 1 week ago
  #5
Here for the gear
 

Quote:
Originally Posted by Roll Tape View Post
I found this interesting on the topic of Green Glue as explained by Dennis Foley of Acoustic Fields.

1.Acoustic Fields: https://www.youtube.com/watch?time_c...ature=emb_logo

2.Acoustic Fields: https://www.acousticfields.com/use-d...oom-acoustics/
This guy goes against everything I've read about the subject. He actually states it in his video. My problem with this is two-fold. One, if you dig deeper into his materials, he talks about this product that they "found" that does a better job than drywall, and green glue, and drywall and green glue together. He also states that it is best useful for the frequency ranges that our voices live in. This is not helpful for a rehearsal/recording studio that deals with all instruments of a MUCH wider frequency spectrum. Second - he's pedaling his own product, for which he gives absolutely zero information about unless you pay him $1,500 to design your studio for your. yeah. No thanks.

I'm going to stick with the information I've found by multiple sources who build studios for a living, who suggest using drywall (of course making sure to hang it properly).


Quote:
Originally Posted by elegentdrum View Post
In general, you will get the best results with a mixture. The idea with glue, or anything, is to get air pockets between the sheets. change in mass helps too, even a layer of foil or plastic. Foam or metal would have a major impact.

for practical sake, I suggest two layers right on top of each other, than one air gap to the 3rd layer. Can be accomplished any way you want, would be simplest using trimming of sheet rock for a 4th layer---of space. One layer of plastic over the air gap will help things out. Could get fancy with the plastic layer over the air gap to keep crumblings out of the room.
I appreciate you chiming in to help, but everything you wrote goes against every piece of material I've consumed over the last 2 weeks (which is a lot). I've read Rod Gervais' book twice, plus all of his posts on the matter on this website forum, as well as hundreds of threads on the topic. Sorry bud, maybe do some more research.


Quote:
Originally Posted by nms View Post
1 tube of GG will get you around 70% of the performance of two tubes. If you're going to use GG, just use 2 tubes/sheet.
So you're suggesting using 2 tubes/sheet for the first sandwich, and then when I put the 3rd layer of drywall on, to use 2 tubes/sheet for that sandwich as well? Instead of 3 tubes for the first sandwich and 0 (or 3) for the 2nd sandwich?

Last edited by Jag94; 1 week ago at 05:22 AM.. Reason: grammar
Old 1 week ago
  #6
nms
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Quote:
Originally Posted by Jag94 View Post
This guy goes against everything I've read about the subject. he's pedaling his own product, for which he gives absolutely zero information about unless you pay him $1,500 to design your studio
$1500 to design the shell. No mention of the acoustic treatment. And yes, Dennis Foley's claims and products aren't particularly well regarded among the regulars here. Bold claims that contradict proven practice by the best in the industry need to be backed up by credible test data and evidence in order to be taken seriously. His responses are elusive when questioned and all of this has led to a bit of a snake oil salesman reputation.
Quote:
So you're suggesting using 2 tubes/sheet for the first sandwich, and then when I put the 3rd layer of drywall on, to use 2 tubes/sheet for that sandwich as well? Instead of 3 tubes for the first sandwich and 0 (or 3) for the 2nd sandwich?
Do not use 3 tubes/sheet. Skip the GG on the 3rd sheet or do 2 tubes. Either way, you'll get great performance out of your wall so long as everything else is on point.
Old 6 days ago
  #7
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Quote:
Originally Posted by elegentdrum View Post
In general, you will get the best results with a mixture. The idea with glue, or anything, is to get air pockets between the sheets. change in mass helps too, even a layer of foil or plastic. Foam or metal would have a major impact.
First, Green Glue is not glue. It's just a name, but the product is NOT an adhesive, and was never meant to be an adhesive. As others have said, it is a CLD compound.

Second, the purpose is NOT to create tiny air pockets! The purpose is to create a damping layer that is constrained between the two sheets: hence the name: Constrained Layer Damping. This works when the Green Glue material resists the shearing forces acting along the plane of the wall, due to the bending and flexing of the panels as the wall vibrates wen sound waves hit it. The Green Glue stuff is very efficient at removing the energy in these shear forces, and turning it into low grade heat, which is then dissipated by both the product itself and also the layers that constrain it. Any air that might be entrapped between the panels is incidental, and has no effect on the process. It is purely a physical process, involving shear forces at the microscopic level.

Third, layers of foil or plastic would do nothing at all. They are not visco-elastic, like Green Glue is, so there would be no shear damping. Thus, no useful effect. Zero.

Fourth using layers with different amounts of mass or different densities is pointless here. It is a myth that it provides an advantage in isolation. The slight advantage that the impedance mismatch produces, is offset by the lost mass, in a normal wall WITHOUT Green Glue, but in this case the layers are not even in contact with each other, so there isn't even that advantage! Using layers of differing density or mass in a wall with Green Glue would give you LESS isolation, not more.

So your statement is completely wrong, on every level.

Quote:
for practical sake, I suggest two layers right on top of each other, than one air gap to the 3rd layer.
That would be wrong advice as well. That would create a 3-leaf system, which always has WORSE isolation in the low frequencies, than the equivalent 2-leaf wall. And small air gaps in a wall have very high resonant frequencies, thus trashing the isolation even more.

Quote:
Can be accomplished any way you want, would be simplest using trimming of sheet rock for a 4th layer---of space. One layer of plastic over the air gap will help things out. Could get fancy with the plastic layer over the air gap to keep crumblings out of the room.
I don't even understand what you were trying to say here, so I can't comment on that directly... except to say that I've never heard or read of such a thing in acoustics.


As others have said: it would be better if you refrained from posting bad advice like this. It only confuses people who are trying to learn how to build their studios properly.


- Stuart -
Old 5 days ago
  #8
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damping per stress layer (may be an other translation will be better)




in google translate

http://translate.google.com/translat...contrainte.htm


in french
http://www.lafontaudio.com/dossiers/c-contrainte.htm
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