Communicating doors in a double wall?

[Vanhoecke]

I'm trying build a HT in the basement with superior isolation. My plans include double wall construction (i.e., two seperate stud walls) between the HT and the adjacent living space. The stud walls will be connected to the ceiling joists with DC-04 isolation clips. In order to maximize the STC I'm loking at installing two seperate doors in the entry. This should be significantly less expenses then purchasing a soundproof door for $2500. Each door will be an exterior grade metal door with a full seal around the door ($250 each). Each door will swing open in an opposite direction. My question is how to install the two door jams. Since there will be a 1" gap between the two walls, I assume I will have something a little less than an inch gap between the two door jams. I don't think I want a ridge connection between the two, since this defeats the whole purpose on installing a double wall. One thought is to use some MLV behind the door jam which will span the gap. Another idea is to use some backer rod and chalk the gap with Green Glue. Does anyone have any ideas?

 

[Savant]

One idea from an Auralex site. This is just a sketch, but should get the point across. The purple triangles represent absorptive material on the interior sides of the doors and jambs. This is not 100% necessary, but does help minimize possible cavity resonance in the door assembly. GG could be substituted for the "StopGap" to close off the jamb-gap without rigidly connecting it. This is usually desirable from an aesthetic standpoint.

 

[Scott R. Foster]

I have a similar situation in my studio... the door jams ended up almost touching do to wall dimension. I filled the gap with an elastomeric [never gets hard] exterior grade caulk [a product made by Thoroseal if I recall correctly]. Work great and has stood up well over the years. If you press on it, it is still soft.

 

[Alex2507]

I would say that you could do your layout to achieve a 1/4" gap in between the jambs. I'm not sure what MLV is but there is an acoustical caulking made by USG. $10 or so for a big tube. It hardens on the outside but the inside stays soft. Kinda cool. There is a product called Deciband and something else called Resiliant Channel aka RC-1 Channel. Let me suggest mineral wool insulation. Any drywall supplier will carry all that. Solid core wood doors might be better. A door supplier would be able to turn you on to the door system used in hotels with adjoining rooms. Good place to at least get ideas and see how they approach those situations. Have a blast.

 

[Vanhoecke]

Thanks for all the input. It seems everyone agrees that using some form of acoutical chalk in the gap is the way to go.

Scott, I googled Thoroseal. All I could find was a plaster mix for waterproofing cement. It didn't appear that it will remain pliable. Was it somethin else? If not, I'll probably use GG since I'm going to be using it between the layers of sheetrock. I think it will remain pliable. I haven't used GG before. Does anyone know if it will span a 1"+ gap or do I need to fill the gap with mineral wool first?

Alex, you indicated that a "Solid core wood doors might be better". Why? A metal exteror door will have much greater mass and will come pre-hung in a frame with a good seal all around the door.

 

[Alex2507]

Sorry to get back so late. I'm just learning my way around here. Wood is better for stopping sound I think. I do know that the double doors used in adjoining hotel rooms are wood and they are all about stopping noise transmission. Automatic sweeps come built in to provide a seal at the bottom. The USG caulk is carried by drywall suppliers. You can even get a weather strip type material to use with your track or bottom and top 2x4's. Home Depot and Lowe's are not your friends in this case.

As far as the mass is concerned I assume you're talking about prehung residential entry doors. They are well insulated for heat and cold, not sound and not nearly as heavy. I wish I knew 1/2 as much about A/V as I do about this. I do this for a living. I'm not proud of it though so mumm's the word. Good luck.

 

[Scott R. Foster]

Alex:

I went back and thumbed through some invoices... I am pretty sure the material we used was made by these guys:

http://www.tremcosealants.com/

but I can't be certain.

In any event I sourced the material with help of a professional in the field of weather proofing and sealing as a large element of my studio build dealt with sealing around openings in a block wall we had filled with grout to yield a truly massive wall section and many elements of the sealing had to be up to snuff for exterior applcations not just to meet acoustic need but to maintain the vapor barrier. We had enough of this expensive caulk left over for a number of interior jobs, such as the control room window and door systems similar to the one you contemplate. This material has stood up very well in these applications.

In the end - for an interior application - the USG acoustic caulk would probably be fine... but for any elements which might cross your vapor barrier on involve penetrations to the exterior or encounter a good deal of "traffic" it is probably worth your while to ask a pro.

Good Luck!

 

[Alex2507]

Hey Scott,
Good points about weather proofing, sealing penetrations and checking with pro's. I was only considering interior acoustical applications when recommending the USG caulk not even thinking about the exterior walls.

 

[Vanhoecke]

Thanks for the input.