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Discussion Starter #1
What are most people doing to maximize the STC of their door walls? I thought I had read once that two doors opening in opposite directions is the most ideal solution when a true soundproof door is not possible. My plan is a solid core door with gaskets and a floor seal. However I won't spent $1000 or more to do this for a real sound proof door, and so far, the solutions I'm finding are closer to $3000. I could have a totally custom made door for less than that, no? What about having a custom door made from two layers of MDF or Plywood and a viscoelastic compound (i.e. a CLD door). Maybe even a layer of mass loaded vinyl adhered to the two wood panels? Green glue won't stick well enough I suspect, but there are urethane polymers that could work I think.


I can get a solid core sound rated door that matches my other house doors for $125 prehung, so for $300 I can get two of them and the necessary materials to add gaskets and such. Is this not the cheapest and simplest solution?
 

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It is thanks. I missed this in my earlier search. The title may have threw me off as I know what STC rating to shoot for, just difficult achieving it.


It is really tempting to just build a door from scratch. There is a mill shop in the area that can custom make a door and when I told them my plan they said they had done similar work for studios in Chicago and would be happy to build to spec. I actually wouldn't use Greenglue in mine but a talc loaded urethane as it does in fact set but remains viscoelastic at mid to low frequencies. I can't speak to how I know this, but this stuff is used in some commercial and tested CLD panels but is sold for molding stuff as well (you have to mineral load it yourself, but otherwise its the same stuff).


Even the stupid door seals are expensive. This isn't my first party and I've worked on creating sound proof doors before. I never had a dedicated space so I never had the option to sound proof with two doors or an entrance hallway, but...I have a sound proof office for work (I work from home) and we installed an acoustically rated solid core door with an STC rating of 37. However what I quickly learned is that the STC rating is for the door, not the door and jam system. It then took a lot of work to raise it to a decent workable value, and realistically, putting some neoprene gaskets around the door aren't working. The problem is that there is simply not enough pressure against the gaskets. The door latch is even adjustable, but its a single point. The door systems built for this use special adjustable gaskets that put pressure on the door themselves and self adjust. They cost a few hundred dollars. I priced out all of them at one point and was nearly at the price of a commercial offering. I need to figure out a better DIY solution.
 

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Bat-wing type seals may be easier to work with if you can't apply enough pressure to compress the neoprene seals. Very little (comparatively) pressure needs to be applied to create a decent seal. I'm guessing you already have a drop-down seal for the bottom of the door too?


^^^ these are the seals I'm using at the moment. My main issue with them is they are so small that I don't have the confidence the door is engaging with them throughout its length. Their specs require a maximum of a 4mm gap between the door and the frame to work effectively, with a recommended space of 3mm or less!


^^^ these are 'bat-wing' seals. They are much larger than the seals I'm using at present, with the flat faces being 12mm each, so should provide a good seal, even if the door is a couple of mm farther from the frame. Very little compression required to make the seal.


^^^ and of course, these are drop-down seals for the bottom of the door - my particular setup has two of these rebated into the bottom of the door. They seem to work well.

Food for thought - and none of the above is expensive.
 

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It is thanks. I missed this in my earlier search. The title may have threw me off as I know what STC rating to shoot for, just difficult achieving it.


It is really tempting to just build a door from scratch. There is a mill shop in the area that can custom make a door and when I told them my plan they said they had done similar work for studios in Chicago and would be happy to build to spec. I actually wouldn't use Greenglue in mine but a talc loaded urethane as it does in fact set but remains viscoelastic at mid to low frequencies. I can't speak to how I know this, but this stuff is used in some commercial and tested CLD panels but is sold for molding stuff as well (you have to mineral load it yourself, but otherwise its the same stuff).


Even the stupid door seals are expensive. This isn't my first party and I've worked on creating sound proof doors before. I never had a dedicated space so I never had the option to sound proof with two doors or an entrance hallway, but...I have a sound proof office for work (I work from home) and we installed an acoustically rated solid core door with an STC rating of 37. However what I quickly learned is that the STC rating is for the door, not the door and jam system. It then took a lot of work to raise it to a decent workable value, and realistically, putting some neoprene gaskets around the door aren't working. The problem is that there is simply not enough pressure against the gaskets. The door latch is even adjustable, but its a single point. The door systems built for this use special adjustable gaskets that put pressure on the door themselves and self adjust. They cost a few hundred dollars. I priced out all of them at one point and was nearly at the price of a commercial offering. I need to figure out a better DIY solution.
You hit on a very key point. Single point latches. I don't subscribe to the "one latch is good enough" camp. The swing out side of the door NEEDS good pressure against the seals. With one latch I don't see how that's truly possible. You can get a GOOD seal, but not a great (dare I say "correct" instead) seal with one latch. The door I have has 3 latches. I've seen SCIFs (where most of this technology really comes from) use the same setup. SEALS and mass are key with these doors.

Communicating doors HELP (and are cheaper depending on where you get the doors/etc), however it's a geometry nightmare for most theaters. How do you handle the one door that swings in (or out?)? Will it hit chairs? Cosmetically does it work? Door handles become more interesting. The list goes on.

If on a budget I would do this:

One door with seals from Zero Int'l (or one of the vendors on the forum), heavy heavy heavy mass (talk to custom door shops in town for options), double or triple latching system, mortised drop down seal with solid door saddle (stone or wood).

The door SHOULD feel like a vault door when opening and closing. If you can slam it, it's not heavy enough!
 

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Discussion Starter #7
Well I think you have to balance this a bit. It's not just mass since the mass controlled region is only part of the issue. Low frequencies are handled by stiffness and the stiffness needs to be damped. In addition, damping helps reduce the transmission through the wall of the lower frequency energy. If I have a custom door made, don't I want them to make it a CLD door and not just a massive door? Don't I also want the core of the door made massive with something other than wood? When you say massive to typical builders, they think lots of plywood or MDF. From what I've seen in STC tests in engineering handbooks, the STC of standard drywall is much higher than plywood or MDF, but MDF is much stiffer than Drywall. It seems like what is best is a composite of different materials (which creates natural impedance mismatches as well) with viscoelastic compound.


I was thinking if I went a custom route, assuming this is feasible, that having an overlap lip for the door that creates a more massive area for the seals would also be good. I could have triple seals for example that way.
 

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The best approach is communicating doors, with seals.



I did this, which was massively OTT and still benefited from another "communicating door" at the end of the small hallway (about 5ft). This door is about 100mm thick with about 10 layers of 10mm mdf sandwiched with green glue, acoustic seals all the way around



 

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Discussion Starter #9
That is a wildly thick and heavy door.


I wonder if part of the reason your sandwich door wasn't more successful was that the door was made of identical mediums sandwiched together. As I understand it the doors are more successful when there are different impedances through the door. The more mismatches the better. The Green glue does change the impedance at that intersection, but its a very thin layer, so I believe that is primarily acting as a CLD and not really impacting the change in impedance. I've noticed there are some builders that suggest alternating MDF, plywood, etc. I wouldn't be shocked if maybe having a central core of drywall would be good, its heavier than the plywood but a lot less rigid.


I'm at such an early stage of planning right now that I don't even know if I can do the dual communicating doors option or not. If I restrict the width of the riser or ensure there is a walk way behind the riser, then I definitely can, but... if I do that then I have the problem that my riser doesn't intersect with a corner and can't be used effectively as a bass trap.


If I'm willing to sacrifice about 6' of room depth I can add a hallway and have two doors that way, but...my models of the rooms response and modes show that the longer room is better. I also think the inner wall then needs to be fairly rigid and overbuilt for the basstrap idea to still work.


At the moment its unsure. At first I was so positive I could do the communicating doors and after hearing some people indicate why they can't, thinking about the most probably layouts for my space, I'm realizing I may not be able to either. The only option that would work without giving up depth is the make the riser narrower in the back on only one side, have the entrance there, but intersection with the other corner. It may mean losing 2 seats in the theater.
 
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