Green Glue vs air gap/room within room

[Ted White]

You'll want that gap between the brick and the new wall frame to achieve good decoupling. Strapping the wall frame to the brick would couple the wall, dropping sound isolation.

[vass]

Thanks Ted,

And once the decoupling is in place with the framing of the inside wall, how much of a would adding the green glue make as apposed to just the double dry wall?

The reason i ask is because there would already be the decoupling of the wall from the brick wall so would it be necessary to spend the money on green glue for further vibration absorption when there is already decoupling in place?

Thanks again!

[Ted White]

Damping the mass assists in both coupled and decoupled walls:

[Sebg]

Ted has shown a test comparison for a staggered stud wall. A staggered timber stud wall will still have some coupling via the top and bottom plates and in the test results I have seen, Green Glue has the most dramatic effect when there is coupling - paradoxically. In a separated stud wall there is less improvement from Green Glue. I have published before a test result of a separated stud wall with/without Green Glue and the improvement was not worth the extra cost. Admittedly, this was just one test series but I have been asking GG for years to publish a test data comparison for a separated stud wall. This is probably not possible at the Orfield Lab that they have been using for testing as it has flanking issues over about STC 55.

[Ted White]

Riverbank Labs tested two double stud wall assemblies. One with, and one without the damping compound. While wet and not nearly polymerized, the damped wall has a 4 point advantage over undamped. Properly dried damping materials would produce greater improvement.

It is unfortunate, as you say, that the manufacturer has not tested a double stud wall with properly dried compound.

Also, the flanking limit at Orfield Labs was increased many years ago into the 60s.

[Sebg]

Ted, 65dB transmission loss at 500Hz is certainly not a flanking limit to sneeze at (and is better than the 58dB that it used to be) but it is still a significant limitation and means that any walls over say STC 58 will have a question mark (in a good way I suppose as the real performance would be higher than the test result, but not ideal when doing comparison testing). regards the tests you referred to at Riverbank; my understanding is that they were not the same test series.

I know that GG continues to do product development - perhaps you can prompt them some more regards double stud tests... Ideally what I'd like to see is a relatively lightweight plasterboard used (two layers of 10mm thick or 13mm thick each side) and a narrow cavity (say 64mm studs + 15mm gap + 64mm studs) - in this way we can best see the effects of GG at the MAM frequency in this wall configuration (if MAM is too low then that won't give us a good comparison).

[Ted White]

The fact that the Riverbank double wall tests were not done back to back does not change the data.

[vass]

Appreciate all the info guys! Thanks!

I think i will test before the second layer of drywall goes on and see where i am with that before deciding where to use green glue on the second layer.

[mpowell]

Originally Posted by vass

Hi,

Im in the process of planning a garage to studio conversion. It is a small room roughly 8' x 12' and 7.5' high.

The room is very small and currently bare brick walls. i planned to frame walls an inch or so inside the room to decouple from the brick and then double drywall. But then to gain some extra space i though about strapping the framing to the brick and using green glue between the 2 layers of green glue. Would that be effective or am i better giving up the space and decoupling?

The garage door will have a double wall system a few feet in front of it (garage is 16' long in total) to help stop sound leaking out there.

any thoughts??

Your help is much appreciated!!!!!

Thanks!

Hello! I'm builing a similar room and have been unclear on how big to make this airspace gap between the brick walls and the framing. Is it worthwhile to have a 6” gap everywhere. Although there would be insulation within the framing, there would not be insulation on the brick or in the gap. Wouldn’t bass build up in this space and become essentially… a drum? Thank you very much for any suggestion you all can offer and for the wealth of information you all provide on this forum!

[Ted White]

You want the LF resonance frequency as low as possible. Two big variables. Assuming a decoupled system, cavity depth and mass both directly establish that frequency. Of the two variables, mass is the more dominant. So given the choice, you'd opt for a smaller air cavity and a third sheet of 5/8" drywall.

Use simple R13 fiberglass in the wall. I'd suggest building the new wall 1" from the brick. That plus the 3 1/2" stud = 4 1/2" air cavity.