72 STC Communicating MDF and Green Glue "Wal-Dor": What to cover the innards with?
Dgrlzmsuga
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#1
30th January 2010
Old 30th January 2010
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72 STC Communicating MDF and Green Glue "Wal-Dor": What to cover the innards with?

I recently added a 12" x 12" x 96" lobby outside my converted basement closet and built two communicating doors out of 2x4 wood and steel studs. Rough measures are 30 x 78.5"; I figure my STC rating on this door will be better than my walls (with the right seals ofcourse) and if I had to guess, maybe around 72-75 STC (60-65 with the 4x3/4" MDF + 8-10 with the Green Glue. Maybe the HDF + Greenglue optional layer adds about 1 or 2 points and that will be bonus. I wanted to cover the innards to prevent the Roxul from being air exposed without creating a triple leaf effect. Would Burlap or Mesh create a triple leaf? My construction is as follows:

Optional:
1/4" HDF with a nice Hardwood Look
Green Glue

Door #1:

3/4" MDF
Green Glue
3/4" MDF
Green Glue on studs
2x4 Wood + Steel Frame stuffed with Roxul Safe n'Sound

4 x 4" Commercial rated Stanley hinges, mortised to jambs and screwed into door "face". Used longer screws to secure through jambs, drywall and wood stud.

4" Airspace

Door #2

2x4 Wood Frame + Steel Frame stuffed with Roxul Safe n'Sound
Green Glue on studs
3/4" MDF
Green Glue
3/4" MDF

Optional:
Treated with Studio foam for room acoustics

4 x 4" Commercial rated Stanley hinges, mortised to jambs and screwed into door "face". Used longer screws to secure through jambs, drywall and steel stud

My idea was looking at the door as an opening into a wal, hence WalDor. Hence, I built a wall with Double Studs. Door is about 5" thick and heavy but the hinges held up great: 16" spacing between hinges and started at around 7". Word of caution, you need to cut 3/8" spacing as opposed to the typical 1/16 to 1/8 to allow for the swing, especially the 1st 2 inches of the jamb. I had used regular jambs from MDF (5/8 and had to rip them out. I ended up using some 1/4 MDF panel wood (comes in packs of 3)









#2
1st February 2010
Old 1st February 2010
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Very interesting stuff, for sure. How did you calculate the projected STC? I assume each door is attached to a decoupled stud wall? So the walls that the doors are sealed to are indeed decoupled?
#3
1st February 2010
Old 1st February 2010
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jhbrandt's Avatar
 

You might as well go one step further and NOT use any fiberglass but fill them with sand instead... they'll weigh about 400lbs each - but what the heck...

Seriously, you can put luan or any thin plywood on the back side of the doors to seal them and make them look nice.

IMHO, you didn't need to make them so thick. It is mass that you needed here - like a solid core door with mass added... Heavy. Your seals will be the weakest link and you should have at least 2 layers of seals for something like you are attempting.

What is the transmission loss of the wall that the doors are in??
#4
2nd February 2010
Old 2nd February 2010
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Hey John,

Good thoughts. I agree on the sand vs. insulation. You think he should do double gaskets? I'm thinking if he used a single line of top end 1" Neoprene all around and an automatic door bottom with similar 1" gasket he should be good. Especially if he kept the tolerances tight (small gaps).

What do you think?
#5
2nd February 2010
Old 2nd February 2010
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jhbrandt's Avatar
 

Quote:
Originally Posted by Ted White View Post
Hey John,

Good thoughts. I agree on the sand vs. insulation. You think he should do double gaskets? I'm thinking if he used a single line of top end 1" Neoprene all around and an automatic door bottom with similar 1" gasket he should be good. Especially if he kept the tolerances tight (small gaps).

What do you think?
Yes the all around Neoprene is excellent but, with all that effort put into the construction of this 'thing' (haha), if he were to add a step (like a bank vault door) on the room side - he could ensure a good seal with the additional gasket on the step.
#6
2nd February 2010
Old 2nd February 2010
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I just think how hard it is to close my (sealed) door sometimes as the door is squeezed up to the seals. How would you adequately compress double seals?
#7
2nd February 2010
Old 2nd February 2010
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jhbrandt's Avatar
 

With a heavy door and proper commercial door closer - it's very easy.
#8
2nd February 2010
Old 2nd February 2010
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What closer might you have in mind? I havent come across one that will maintain constant pressure and allow the door to be opened easily without flipping a switch to release the tension.
#9
2nd February 2010
Old 2nd February 2010
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jhbrandt's Avatar
 

Yeah, well you may have a point there. I'll have to look up the ones we used in the last install. I don't remember. Here in Indonesia things are different with different products, which I will have to deal with soon.

The seals do not actually need to compress much... if the Neoprene is V shaped the leading edge is easily compressed enough to make a good seal. We're not trying to support a different pressure environment like on a submarine or spaceship - but the idea of sealing is the same.

John
#10
2nd February 2010
Old 2nd February 2010
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You're right about the seals not needing to compress much.
Dgrlzmsuga
Thread Starter
#11
3rd February 2010
Old 3rd February 2010
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Thread Starter
Quote:
Originally Posted by Ted White View Post
Very interesting stuff, for sure. How did you calculate the projected STC? I assume each door is attached to a decoupled stud wall? So the walls that the doors are sealed to are indeed decoupled?

To my understanding, STC ratings on doors are achieved by caulking it into a frame and testing. That said, I arrived at the estimate as follows:

Most wall contruction and even Rob Gervais rates double stud wall partitions with an air space and both cavity stuffed with mineral wool and covered with 2 sheets of 5/8 Drywall on both sides as high as 63 STC. Since what I did was essentially build a double stud wall, cut out an opening and hung it on hinges: 2 sheets of 3/4" MDF I should easily attain that 63 STC rating and even exceed it. Green Glue purports to add 8 - 10 STC points so that takes me up to 71 point level. Throw in a layer of the HDF and I think I achieve the 72 point on the "Wall-door"

Yes. The Double Stud Lobby is decoupled from the opening, caulked with silent seal. I also threated the ceiling of the lobby and floated it. Green Glue used between all partitions.
Dgrlzmsuga
Thread Starter
#12
3rd February 2010
Old 3rd February 2010
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Thread Starter
Quote:
Originally Posted by jhbrandt View Post
You might as well go one step further and NOT use any fiberglass but fill them with sand instead... they'll weigh about 400lbs each - but what the heck...

Seriously, you can put luan or any thin plywood on the back side of the doors to seal them and make them look nice.

IMHO, you didn't need to make them so thick. It is mass that you needed here - like a solid core door with mass added... Heavy. Your seals will be the weakest link and you should have at least 2 layers of seals for something like you are attempting.

What is the transmission loss of the wall that the doors are in??

Good points on the two layers of seals. I will incorporate this. As for the door construction, I wanted to get away from normal door construction and focus more on techniques employed in wall construction. Given that a Double Stud wall yields the highest STC ratings in an assembly, my goal was to then build such an assembly, slide it in front of my opening and cut an opening into it and hung that opening unto hinges. That was my vision of what a 'door' is. Constructing a heavy "Super Door" with say a sandwich of lead like Gervais outlined was out of the question (budget constraints). The doors hang inside the double stud lobby that I constructed. I used two layers of 5/8 Drywall sandwiched with Green Glue in the build.
Dgrlzmsuga
Thread Starter
#13
3rd February 2010
Old 3rd February 2010
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Thread Starter
Quote:
Originally Posted by Ted White View Post
Hey John,

Good thoughts. I agree on the sand vs. insulation. You think he should do double gaskets? I'm thinking if he used a single line of top end 1" Neoprene all around and an automatic door bottom with similar 1" gasket he should be good. Especially if he kept the tolerances tight (small gaps).

What do you think?

I am thinking of using a product call Perfect Seal. They are 1":

EMP Industrial - PERFECT SEAL - expanding sealant tape

I used 2 1x2 MDF strips to frame the jambs and the doors will close against these. I have left (1/8 gap between door and jambs for a tight seal against the sealant tape) all around. I had initially thought of also sealing the door about two inches before the built up jambs as well for a double seal, all around.
Dgrlzmsuga
Thread Starter
#14
3rd February 2010
Old 3rd February 2010
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Thread Starter
PS...

What can I cover the insides with? I want to prevent the roxul from becoming airborne (although my doors will in theory be air tight) and want to avoid a triple leaf. Would burlap or a fire rated fabric suffice?
#15
3rd February 2010
Old 3rd February 2010
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jhbrandt's Avatar
 

Quote:
Originally Posted by Dgrlzmsuga View Post
What can I cover the insides with? I want to prevent the roxul from becoming airborne (although my doors will in theory be air tight) and want to avoid a triple leaf. Would burlap or a fire rated fabric suffice?
Yes. If you buy fabric such as burlap make sure it is fire rated.. if not, I think you can treat it with a spray that will help.. check into that.

OR simply buy upholstery fabric like you would use on a couch. This works very well for fiber containment. It does not need to be transparent to HF as an absorption panel needs to be.

Cheers,
John
#16
3rd February 2010
Old 3rd February 2010
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amishsixstringe's Avatar
 

Quote:
Originally Posted by jhbrandt View Post
Yes. If you buy fabric such as burlap make sure it is fire rated.. if not, I think you can treat it with a spray that will help.. check into that.

OR simply buy upholstery fabric like you would use on a couch. This works very well for fiber containment. It does not need to be transparent to HF as an absorption panel needs to be.

Cheers,
John

John,
What type of "spray" are you talking about? I am trying to find something similar to keep compressed fiberglass (0c703) from going airborne in some hvac register boxes without having to wrap or cover it.

I do not want to hijack the thread, but thought others may find it useful as well. Thanks,

Neil

Carry on...
#17
3rd February 2010
Old 3rd February 2010
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jhbrandt's Avatar
 

Flame ******ant Spray

#18
3rd February 2010
Old 3rd February 2010
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I wasn't paying close enough attention and initially inferred that you estimated a (single) door would have an STC in the 70s.

You could cover the insides of the doors with a Guilford of Maine fabric. All fire-rated acoustical fabric. Many colors and patterns. Look at the FR series.

Have a look at the dialog between John and me regarding the double seals vs. closer requirements.

Also, I would look at a seal system that is adjustable and tested. Tape isn't adjustable.
#19
4th February 2010
Old 4th February 2010
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Quote:
Originally Posted by Dgrlzmsuga View Post

Most wall contruction and even Rob Gervais rates double stud wall partitions with an air space and both cavity stuffed with mineral wool and covered with 2 sheets of 5/8 Drywall on both sides as high as 63 STC. Since what I did was essentially build a double stud wall, cut out an opening and hung it on hinges: 2 sheets of 3/4" MDF I should easily attain that 63 STC rating and even exceed it. Green Glue purports to add 8 - 10 STC points so that takes me up to 71 point level. Throw in a layer of the HDF and I think I achieve the 72 point on the "Wall-door"
This assumes 100% effective seals and a linear effect of Green Glue above and beyond the sound transmission loss of a double stud wall. In addition, the two faces of your "wall door" are not independent walls; each side is attached to the 2 x 4 frame, so you do not really have a "double stud wall". Do a sound test with a sound level meter; just crank the music on one side of the door at about 80-90 dB and measure the sound level on the other side. I would be astounded if you really observed the sound attenuation you claim.
#20
4th February 2010
Old 4th February 2010
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I must say here that I think that I was a little too vague in my comments early on... suggesting that you fill it with sand.

I agree with Miles. If you get better than 48 - 50 it would be great but I think that it will probably be close to that due to sealing difficulties with that massive construction - not to mention the flanking paths of the door framing...

Good luck!
- John
#21
4th February 2010
Old 4th February 2010
  #21
Gear addict
 

Yes, this all boils down to seals. The doors would be decoupled, however, as each is independently mounted to its own decoupled frame. Double stud walls are being used, right?

The Green Glue is not linear, just as Miles pointed out. Comparison of double stud configurations may suggest a gain of maybe 4-6 points in a double stud configuration. The data is sketchy.

Like John mentioned, seals around and through the door framing (jamb) is also possible, as well as seal failure between the door and jamb.

Lastly, there may be some issue in the low frequencies with the door mass not being contiguous with the wall mass. I believe more effective damping would theoretically occur if the wall was a solid, uninterrupted layer.

Having said all this, the doors sound excellent, and you have to have doors, obviously. Not sure what the resulting STC or OITC might be, but if you take care with the seals, you should be quite happy.
Dgrlzmsuga
Thread Starter
#22
5th February 2010
Old 5th February 2010
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Thread Starter
Thanks, Guys--- A Lot to Think Of....

Thank you everyone for the response. Seems that my challenge will be to create proper sealing. I will also take Miles advice and test the door with a sound meter. That's obviously the real world test. I will post pictures and maybe a video on the results when I complete my project. My next task is acoustic treatment of the converted closet with probably Studiofoam. I will keep you posted.
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