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post #1 of 19 Old 09-29-2017, 02:00 PM - Thread Starter
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Q&A on Soundproofing and Door Options

I've received a bunch of messages about door soundproofing and thought it would be helpful to share what I found in my research into the topic. I live near a well known acoustics testing lab and began exploring a few things. First was just the ability to buy a soundproof door. The cost was very high and the complications far greater than anticipated. Then I looked into manufacturing a custom door and having it tested at this lab (They were nice enough to deter this waste of money and give me access to existing test data). This will ensure that if I do ever go down this road of having a door maker manufacture such a custom door, I have good reason to believe it will have high TL to begin with before spending time and money having it tested.

Ok first some of the problems.
  1. Doors are nearly always the weak point in a soundproof wall
  2. Door seals are rarely the weakest point in a door that was not constructed for sound proofing
  3. The door jambs are a flanking path and often the weakest link in the door structure
  4. High STC doors installed in high STC walls require highly massive door frame installation, as in with cement and metal
  5. High TL over a wide bandwidth requires a large air space, a single door cannot achieve this
  6. Thick, massive, solid structures can transmit sound readily. Remember that sound transmits easily through a foundation
  7. Stiffness is the enemy of TL above the resonant frequency and below the coincidence frequency, undamped resonances further reduce TL at the top and bottom of the the curve

The above truths tell us a few things we need to know. First, that a door creates a hole in our walls that becomes the weakest link. Therefor, like any other penetration, the smaller the hole the better. Large doors, worse yet, double doors (french doors for example) are a bad idea. Small doors aren't as dramatic looking and make the movement of large equipment more difficult.

The next thing we can infer is that a communicating door assembly is the best option. There is no single right way to do a communicating door, but there are certainly wrong ways. Any distance between the doors is good, it creates that airspace I mentioned above and allows a door that is more similar to the wall (remember that a party wall has drywall on two sides typically and the TL of that wall is partially dependent on how thick the wall is). There is no official minimum distance, but anything greater than 12" will cause the two doors not to "see" each other acoustically anymore. This isn't a problem per say, but it does mean that 12" is a good maximum. Once you go to say 3 or 4 feet, you are creating a hallway. If you have a hallway, then you do introduce some other problems to consider, but for the most part this is the best solution. You want to ideally offset the doors so they are not inline with each other if possible. In addition, acoustic insulation on the walls, doors, and ceiling are helpful. Remember that this adds a few STC points to a wall structure, same with the doors. The difference is small, but something is better than nothing.

Door Frames, the Weakest Link
The door frame is an obvious weak link, and I'm often surprised that more people don't comment on this issue. Door frame's are typically shimmed in place and this leaves an airgap around the frame. The traditional construction technique would drywall the opening and insert the door afterwords. The space around the door is then covered with moulding. This is a big problem and creates an obvious flanking path for sound around the door. There are a few solutions for this. First is that you can install the door frame before drywall and then drywall over the door frame. If you do that you need to deal with an exposed drywall edge, but it allows you to seal the door frame to the drywall and puts a lot of mass. You need to caulk this as well. Another option is to cement the door frame in place once its shimmed, then "glue" the moulding around the frame with acoustic caulk.This is similar to the technique used by studies with steal soundproof doors. The metal frame is cemented in place. It is not uncommon to use a damped polymer cement, which is why I did. It's an additive that makes the cement more flexible, and of course, damps the cement acoustically. The Drywall approach is quite frankly cheaper and easier and I suggest that as a better option.

STC and TL for DOORS
Ok first let's talk about common STC values for doors. MDF has an STC value of about 25 for panels 16mm or greater. Oddly enough, little data is available for thicker panels and what data does exist suggests that thickness doesn't matter much, the STC doesn't increase. TL values are pretty constant. Mass law tells us this shouldn't be true, so whats the reason? The primary causes are speculated to be a result of the structural resonance of the slab assembly and the coincidence frequency. There is a dip in TL at those two frequencies and it doesn't change with thickness. The only change is the frequency, but making a door also makes it more rigid, so these two factors fight each other, and in fact thicker slabs often have a higher resonant frequency. Also keep in mind, plywood and solid wood both have STC values of closer to 15-20 points, quite a bit lower than MDF.

Additionally, there are many solid core doors in which the solid core material is made from light weight wood products or fiber products that have low STC values. As a result, these assemblies have STC values in the low to mid 20's.
https://www.masonite.com/pdf/accoust...ceInterior.pdf
Notice that DorCor and Particleboard have similar STC numbers. DorCor is a low density product and I suggest avoiding it for theater doors. I almost fell for this myself.
https://www.masonite.com/docs/defaul...rsn=55e8ffa3_5
These are commonly used as theater doors, but they are not good sound proofing doors. They have a relatively low STC rating. The core is noted as "low density."

Notice in the first link that the highest STC door value is obtained with a mineral core raised panel door that is 1 3/4" thick. The STC value is 35, and in fact, for cheap doors, its about as good as I could find. I have one of these for my doors and one flush series 1 3/4" particleboard door, which actually has a lower STC of about 32. The mineral core is actually a core similar to that of drywall, it is denser than fibercore or MDF and it has better internal damping. That is why the door has the highest STC and in fact, this is how most true high STC doors are made. With a thick damped mineral core, not MDF.

http://downloads.bbc.co.uk/rd/pubs/reports/1994-14.pdf
This is an interesting study done by the BBC on door slabs and its helpful to see that thicker wood doors really don't help the situation much at all, and in fact, damping is only marginally helpful. Their best door had a lead lining originally but they found that damping MDF worked about as well, as did an air gap, i.e. a hallow core door. Again, this shouldn't be shocking, especially when you see the Masonite data that shows a hollowcore door and a solidcore having similar STC values. Also notice that the bitumen vs just same MDF aren't that different, that the damping layer is reducing the coincidence dip, and that is the primary advantage. In fact studies into CLD have shown that in many cases damping does not add any TL below coincidence or above resonance. That its only benefit is damping the negative effect of the resonance. In some cases ,which well damped materials, there is no advantage at all, the only difference can be attributed to the change in mass.

This may lead you to think that the clear winning option is to add a sheet of MDF with green glue to a slid core door and be done with it. This is actually not a terrible option, but a few things to note. Some here have done this. The gain in transmission loss over the standard solid core doors is modest but meaningful, at low frequencies there will be no difference, but at mid and higher frequencies the difference will be about 3-6 db's more loss. You may see as much as 9db's of loss gained at the coincidence frequency of 3.8khz. Any damping of the door would make a difference however and in fact this sandwich only adds about 3dbs extra loss at the coincidence dip and nearly nothing at other frequencies. Consider that most people have a door that has an STC value of 25, a typical wall will be STC 40 to STC80 (Depending on construction). That means the door is not STC 28, the wall is still twice or more as soundproof. The door is still a huge weak point.

Notice that the winning door they tested was a hollow core door constructed of two sheets of 18mm and 9mm MDF with bitumen damping and wool insulation in the hollow core. Clearly not what we are used to seeing. This is a better door option than simply adding a big sheet of MDF to an existing door with green glue as it provides the best sound isolation. This appears to follow an STC curve that may be in the high 30's to low 40's. This is better than most commercially available doors.

Exterior Entry Doors ARE NOT better than interior doors for soundproofing
There is a common belief that exterior entry doors provide better sound isolation than interior doors. This just isn't true. They actually roughly equal an interior door, and in many cases are worse. They do have a benefit, many come with a threshold and gaskets pre-installed, but these gaskets are not designed for the best sound isolation. A lot of exterior doors are insulated and low mass, with poor damping, and this leads to relatively low STC ratings.
https://www.masonite.com/docs/defaul...rsn=f440f6a3_4
Here is Masonite test data on their entry doors. I've looked around and found comparable numbers from others. Some have doors with much higher values, but often these same companies make similar interior doors with much higher numbers as well. For those who noticed two entry doors that show much higher STC values in the 40's, note that is tested with a storm door. That is a communicating door assembly with a very low mass second door. That should tell you something. An airspace and second door makes a huge difference.

Mohawk has an STC rated door, it is about 10 points higher than their other options:
http://www.mohawkdoors.com/PDS%20She...5_45_90min.pdf
but we are still looking at just STC35. Note it is a mineral core door.

Communicating Door Assemblies are the Best!
http://www.soundisolationdoors.com/p...solation-door/

There is just no getting around this. Two doors is always better than one. This site gives the best approachable information on the topic I could find.

http://eggersindustries.com/wp-conte...Sheets-SG4.pdf
This specialty door manufacturer has high STC rated doors and does so only with communicating doors.

I could not find any test data on communicating doors made with standard MDF core doors. Based on some proprietary test data (Not proprietary to me, but I can't share details) and various links I have found, two doors back to back would give a 3db addition to STC. Adding 6 inches will add about 3db's. Each additional 6 inches adds about 1-3 db's. At some point you hit a limit, no more gains to be had without upgrading the doors. My own door assembly has a 12" air gap and a roughly 45 db average transmission loss. It should be noted that at 45 db's of loss or more, I am at or below the measurement limit that is possible. I cannot measure below 40db's reliably at most frequencies, and the ambient noise outside my theater is at or above 45 db's. That means that I must play my stereo at or above a constant 100db's, and while the system can handle it, that puts high stress on the system. The transmission loss at high frequencies is so great that I cannot measure it, I am at my noise floor.

Gaskets for Doors on Soundproof Walls

First, look at this test data
http://content.assaabloyusa.com/cs/g...dss1012247.pdf
and notice the benefit gained from the various gasket sets for a given door's STC rating. Now look back to the values we found for typical doors we use. Standard silicone stick on gaskets with acoustic thresholds work just as well as any other option on doors up to STC 42, and in fact, there is little to be gained up to STC 45. The adjustable gaskets and adjustable automatic door bottoms do not provide benefit until you hit about STC 49 and above. Notice that not even the custom BBC door met that criteria. That tells us that unless you bought a custom high STC door, these gaskets are not a huge benefit.

I think people should buy what they like, the kits are easy to use and you know they won't be the weak point. However, they are also expensive. I suggest that people consider the stick on gaskets and thresholds first and if looking at two different options, one more expensive than the other, don't assume you get any acoustic benefit. There is no acoustic benefit to the expensive gaskets and bottoms over much cheaper products.

High STC ratings above 50 always are hurt by even the best gaskets, and so the only option becomes more advanced solutions like multiple gaskets and vault like closures. Often these doors are large, thick, metal, and use double or triple seals that close with magnets.

Myths I wish would die
  1. Outside doors are better for sound isolation than inside doors
  2. Simply adding more mass increases transmission loss
  3. Door gaskets are the weak link
  4. The door jamb doesn't matter
  5. You can achieve equal or better results to a basic communicating door assembly with a single heavy and thick door with quintuple gaskets
  6. A thick solid core door with 1/2" MDF and Green Glue can provide huge benefit over a standard door (As mentioned earlier the benefit is actually small)

Key Take-away, what should you do
To be honest, probably the best option for most will be either a)Cheapest bang for buck is the communicating door approach with large as possible air gap and high as possible STC rated doors, or b) buy a professional high STC door and install properly. For those doing the Communicating door approach, damping the door assembly will increase transmission loss at coincidence frequencies. Doing so with a single door is ok, adding another layer of MDF and green glue will certainly be better than nothing, but it's important to know that this is offering only 3-6db's of additional transmission loss and only at certain frequencies. It will not stop any more bass, and in fact, because of the added stiffness may block less bass.

Possible DIY Option
My idea for a possible ultimate DIY door would be to create one using the approach the BBC tested, but enhanced with additional materials. I would consider creating a door with half inch MDF faces and framing. Total door thickness should be as thick as possible, but a minimum of 2" and preferably 3"-4". The core should laminate 5/8" drywall and lossy adhesive (like green glue) to the MDF faces. The core should have a 1" air gap with fiberglass insulation. Both layers of MDF should be damped with greenglue and Drywall if possible. That of course creates a problem, as the door would end up being more than 3.5" in this scenario. It is possible that only 1 layer of green glue and drywall is used, and that 1/4" masonite and green glue are adhered to the other layer. Bitumen damping could also be used for the MDF damping. The next hard part will be the door frame. It should be made of MDF and will need to be installed in a manner that is acoustically sealed, damped, and massive. As I said, I used a damped cement adhesive product for my two door frames, again, with an airgap. I further glued the moulding in place to ensure a good seal.

I would like to try building such a door as mentioned above. I plan to try making one that fits in my existing 1 3/4" slab door frame and so will need to use thinner material. I also want to have it tested if possible as I think it would be great to know that it works.
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post #2 of 19 Old 09-29-2017, 02:11 PM - Thread Starter
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http://9dc159b43a66b1fe0a49-bd2073f7...ic-ratings.pdf

The Jeld Wen Tria R series was the cheapest available door I could find with a good STC rating. I would have gone this route myself but it still was expensive enough to create budget problems for me. The difference between this door and the ones I have is relatively small.

I also just checked and found I mis-remembered what my interior slab flush door is. It isn't Masonite, it was Mohawk by Masonite MDF flush. They don't publish their STC data but emailed me the sheet, which is how I figured out what I had. The STC for that slab is 37.


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post #3 of 19 Old 09-30-2017, 08:32 AM
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Good stuff! If you have more info to post on the polymer concrete damping compounds please do - links to products used, references to people using them to seal the gap between jamb and drywall etc.This seems like an area where you want the material to be able to flex otherwise cracks will just develop?


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post #4 of 19 Old 09-30-2017, 02:36 PM - Thread Starter
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Originally Posted by Nyal Mellor View Post
Good stuff! If you have more info to post on the polymer concrete damping compounds please do - links to products used, references to people using them to seal the gap between jamb and drywall etc.This seems like an area where you want the material to be able to flex otherwise cracks will just develop?


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I made up the compound myself through trial and error using a mixture of casting urethane, Portland cement, flexible thinset mortar, and green glue.

However I later found this:
https://www.usg.com/content/usgcom/e...ca-durock.html

I bought a bag and tried it. I think it's just as usable as what I created. I had some large gaps that needed filling around a duct and used this with some drywall and it held well. I added fine glass beads and talc for damping. Those ingredients were based on a suggestion from someone who cast speaker enclosures in urethane and found the best damping of the urethane required these additives.

I believe that there are a lot of flexible cements now and may be even better options. Most are made flexible with latex or vinyl. I happen to think urethane is better for this, but it has a set time that wasn't impacted by the addition of cement. It makes it really hard to work with. You get maybe 20 minutes before it's too hard to use anymore. That means adding the urethane last and doing it in batches. The urethane I used was shore 30d and designed for mineral loading.

I wish I had taken pictures but it was so messy that the last thing on my mind was bringing a camera or my phone. If you mix the stuff too thin then it won't stay put. Too thick and it won't flow through the gun and into the crevice easily. You also need to do it in layers so that it sets properly. I did 4" thick along one side of the door and it was still tacky after 2 days. When I did the rest in 2-3 hour intervals it seemed to work better.

Since this is very similar to how professional soundproof door frames are set I have to imagine they have a good trick or approach. I used the flexible product for damping and isolation, not crack prevention. That's a good thought that Portland cement would probably crack.


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post #5 of 19 Old 10-02-2017, 08:51 AM - Thread Starter
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Hallway style entryways-What are the benefits, what are the problems?

I mentioned above that once you create a distance between the doors that exceeds 12" they no longer acoustically see each other and you start to create new problems. I also mentioned that this is still a best case scenario in some ways, so while it causes problems, it also has benefits.

Communicating doors typically refer to back to back doors and are typically within 12" of each other. Acoustically this is a good scenario and provides a large amount of sound isolation.

However, in large studio's that need to maintain a high degree of transmission loss to other spaces, or worse yet, anechoic chambers, you tend to see a different approach. These spaces typically have hallways with indirect paths into the soundproof space. The benefits of such a space are that since sound volume decays as it expands (Inverse square law) this greater distance helps dissipate more sound and reduce the amount that escapes. It also reduces direct paths for flanking (such as door jambs or door knobs inline with each other). However, to be more effective, other things have to remain true as well. The hallway needs to be fairly soundproof to be maximally effective. If the ceiling is a false ceiling or the walls are thin lightweight construction then much of the sound will escape through those paths. While it is still much better than not having the hallway, it may no longer be better than just a typical communicating door assembly.

If the hallway is acoustically isolated, you have a new problem. The sound can only spread within the space of the hallway, it is not a chamber. Because there is nothing to convert the sound energy to heat and because none of the sound can escape, the total energy of the soundwave does not diminish. Technically sound will always dissipate energy into heat, even in a perfect 100% reflective space. Air alone provides enough resistance for this. However, for our purposes, this is a small effect. In addition, we have a hallway which is acoustically a tube and so resonances along the tube can develop. The hot spots (high pressure zones) along the length of the hallway can cause weak points in the soundproofing. If they Align with a door, it is likely the TL at those frequencies will be very low. If not, if they align with the walls/ceiling only, it still can create places where natural flanking paths allow sound to escape. Resonances can actually create sound levels that exceed the fundamental during a period of decay, so this can be quite serious. This sound could even leak back into the room much delayed from the original signal. What this means is that the large air space around a soundproof room is good, but just like we damp the inside of our walls to stop standing waves, we need to to do the same in the hallway. It's also good to consider the dimensions of the hallway and calculate its modes. Check these against the resonant frequencies of the walls and concident frequencies of the material (very unlikely that a mode would equal a coincident frequency which is typically well over 1khz). It's also important to acoustically treat the inside of the hallway. I would probably make it a soundproof structure but then install a false ceiling so that at least 6" of fiberglass insulation could be installed overhead. I would likely then install acoustic panels that are biased toward LF absorption along the walls, especially on the apposing short walls. I would also consider strongly putting bass traps in the corners. Finally, if I did have a resonance in the hallway that is causing a weakpoint in my TL, I would find its source and use targeted tuned traps to dissipate the sound energy.

Hopefully you can see that hallways, while providing benefits, can also provide challenges that require careful planning.

In fact, in general, any time you create a long tunnel in an acoustic space, consider it a problem space that must be addressed. A soffit can also create standing waves that compromise the sound proofing at certain frequencies along hot spots in the soffit. By simply breaking up the soffit space with acoustic insulation in the path (and even creating solid breaks along the path) you can mitigate the problem.
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post #6 of 19 Old 10-02-2017, 11:12 AM
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This is great info, Mpoes12. Thanks for researching, doing your own studies and posting this!

Expanding on the benefits of your "hallway" idea, apply the same principles, but instead of a "hallway", use the space for a "foyer" or "lobby", or other similar transition space between the theater and the rest of your home and you get all of the same benefits with a space that adds functionality as well as sound isolation.
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This is great info, Mpoes12. Thanks for researching, doing your own studies and posting this!



Expanding on the benefits of your "hallway" idea, apply the same principles, but instead of a "hallway", use the space for a "foyer" or "lobby", or other similar transition space between the theater and the rest of your home and you get all of the same benefits with a space that adds functionality as well as sound isolation.


Yes Absolutelt true. In fact if you make it a useful space like this then it may no longer be shaped like a tube and the furniture will help break up some of the standing waves. Maybe add in a few chairs and a table and all the better.

I'm working on another post like this around acoustic panels. Nothing new, but I find far too many people avoiding proper materials due to difficulty in obtaining, shipping costs, etc.

Here's a teaser pick of one of the pieces.


That's 24"x24"x36" for scale.


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post #8 of 19 Old 10-05-2017, 07:25 AM
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Originally Posted by Mpoes12 View Post
http://9dc159b43a66b1fe0a49-bd2073f7...ic-ratings.pdf

The Jeld Wen Tria R series was the cheapest available door I could find with a good STC rating. I would have gone this route myself but it still was expensive enough to create budget problems for me. The difference between this door and the ones I have is relatively small.

I also just checked and found I mis-remembered what my interior slab flush door is. It isn't Masonite, it was Mohawk by Masonite MDF flush. They don't publish their STC data but emailed me the sheet, which is how I figured out what I had. The STC for that slab is 37.


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Thanks so much for taking the time to post all this information. I've been struggling with finding a door and haven't received much help.

Do you remember what the cost was for that door you linked to above? Also, do you have a link to what you ultimately purchased?
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Originally Posted by Spyderturbo007 View Post
Thanks so much for taking the time to post all this information. I've been struggling with finding a door and haven't received much help.

Do you remember what the cost was for that door you linked to above? Also, do you have a link to what you ultimately purchased?

I can't fined the direct links you would want. My suggestion would be to see what brands of doors you can get locally. I didn't choose Masonite or Mohawk because they are the best options, I chose them because they were available from one of my local suppliers. I did consider ordering doors online, but ultimately decided that it was smarter to go local.


I can't find the quote I was sent on the Jeld Wen door, I'm not sure if I got that in person or by email. I just recall getting the price and deciding that for two doors it was too much. I want to say it was like $300 or $400 each.
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post #10 of 19 Old 10-09-2017, 12:58 PM
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Thanks for posting the data and results of the research you put into your project!

I'm building a home office at the end of a basement game room used by noisy kids. I've built a 9' staggered wall with mineral wool insulation and double drywall w/green glue on one side. The room is a challenge because it has an adjacent room and a lot of piping penetrations in the ceiling area - so lots of ways for sound to sneak in.

I'm now ready to purchase and install a single 32" door.

Questions:
1) Do you recommend a flush face door as opposed to a panel door?

2) Any particular brand/model door you recommend? Or do you think the STC manufacturer numbers are reliable enough to go on? I will most likely be purchasing from HD or Lowes.

3) Do you think split/jamb prehung doors are acceptable?

4) Do you suggest filling the gap around the jambs with insulation and/or spray foam? And caulking the door trim with acoustic sealant?

5) Use regular gap filling materials to seal the door when closed.

Anything else you think I should keep in mind?

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The wife has asked.... about adding a sliding 'barn door' (I blame pintrest). She asked mostly for aesthetics, but has anyone thought about going down that path for creating as a point of soundproofing

Have not researched much on tracks/etc. I could see the possibility of making a larger than the opening by ~8in MDF built up sliding door that would be a double/communicating door to cover a 'standard' door. The thickness could be a design point. Would not have to have the swing stability that a thick heavy door would need. Would be worried about it rattling with heavy bass. Could add a guide at the end to seal it back to the jam/weatherstripping around jam.

Sure it would be an engineering evolution to build, but would solve some issues but likely introduce other issues.
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post #12 of 19 Old 10-10-2017, 04:53 AM
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Originally Posted by BSHuff View Post
The wife has asked.... about adding a sliding 'barn door' (I blame pintrest). She asked mostly for aesthetics, but has anyone thought about going down that path for creating as a point of soundproofing

Have not researched much on tracks/etc. I could see the possibility of making a larger than the opening by ~8in MDF built up sliding door that would be a double/communicating door to cover a 'standard' door. The thickness could be a design point. Would not have to have the swing stability that a thick heavy door would need. Would be worried about it rattling with heavy bass. Could add a guide at the end to seal it back to the jam/weatherstripping around jam.

Sure it would be an engineering evolution to build, but would solve some issues but likely introduce other issues.
Tell her, "No sliding barn door for you!" lol

Seriously, tell her no. Those doors are going to be out of fashion soon enough anyway.
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post #13 of 19 Old 10-10-2017, 06:42 AM
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Seriously, tell her no. Those doors are going to be out of fashion soon enough anyway.
that is what they said about Rock and Roll in the 50s.
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post #14 of 19 Old 10-10-2017, 06:53 AM
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I actually think we are moving more toward movable and/or disappearing walls. The barn doors will get bigger. As the pressure to maximize the utility of any given space increases (supply and demand) the desire to create spaces that can be reconfigured to fit the occasion will foster innovation. I can't count the number of basement projects discussed here where there was interest in creating a large open entertaining space but having the ability to close it down for an intimate light and sound controlled screening room.
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post #15 of 19 Old 10-10-2017, 07:12 AM
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I actually think we are moving more toward movable and/or disappearing walls. The barn doors will get bigger. As the pressure to maximize the utility of any given space increases (supply and demand) the desire to create spaces that can be reconfigured to fit the occasion will foster innovation. I can't count the number of basement projects discussed here where there was interest in creating a large open entertaining space but having the ability to close it down for an intimate light and sound controlled screening room.
During conceptualization I considered creating a wall slab (4' by 8') that would open conventionally and give the impression of an open room. I decided to settle for a regular 42" door.
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post #16 of 19 Old 10-10-2017, 07:28 AM
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I've seen conference rooms that had sections of floor to ceiling panels that were on tracks to make smaller spaces. You might get some ideas from a google.
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post #17 of 19 Old 10-10-2017, 09:37 PM - Thread Starter
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Thanks for posting the data and results of the research you put into your project!

I'm building a home office at the end of a basement game room used by noisy kids. I've built a 9' staggered wall with mineral wool insulation and double drywall w/green glue on one side. The room is a challenge because it has an adjacent room and a lot of piping penetrations in the ceiling area - so lots of ways for sound to sneak in.

I'm now ready to purchase and install a single 32" door.

Questions:
1) Do you recommend a flush face door as opposed to a panel door?

2) Any particular brand/model door you recommend? Or do you think the STC manufacturer numbers are reliable enough to go on? I will most likely be purchasing from HD or Lowes.

3) Do you think split/jamb prehung doors are acceptable?

4) Do you suggest filling the gap around the jambs with insulation and/or spray foam? And caulking the door trim with acoustic sealant?

5) Use regular gap filling materials to seal the door when closed.

Anything else you think I should keep in mind?


Good questions.

1) the idea behind flush face doors is that they are thicker and more massive. I found some panel doors (including the one I bought for my outer door) that had the panels added onto the middle slab. I forget now what they called this but it means the doors minimum thickness is the same as the slab and the “panels” actually add mass. For doors with composite cores I honestly question how big a difference it makes. The STC values are typically the same.

2) I don’t have a particular recommendation. Yes I think the STC values are honest. They are typically tested by third parties in special labs. The data from those labs is meant to be reliable and comparable (that is arguably not true for absorption testing but I see no reason for big issues with transmission loss testing). The main concern with comparing test data is that some test glued in place and some test with a gasket set. If you don’t know a lot about those gaskets it could be hard to compare.

As mentioned earlier there was a Jeld Wen door series that had a higher STC rating. I’m sure there are other brands with similar rated doors. That one stood out to me.

3)I think a split jamb is ok as long as it’s made of solid material. There is an arguable advantage to having that split in preventing sound from radiating through the jamb.

4) in my first post I mentioned that the door jamb is one of the biggest sound leaks. The gap must be filled to reduce this problem. You could use insulation or foam but it would be no different than adding insulation or foam around a hole in your wall. It will help, especially at high frequencies, but it won’t be ideal. You want mass. I used a mixture of drywall and a flexible cement to fill the gap around my door. I used the drywall to shim the door in place. Once it was shimmed and nailed, I filled the remaining gap with the flexible cement. Once that dried I put the trim around the door frame with acoustic caulk. If your gap is smaller than mine you might shim it the traditional way and then fill the remaining gap with the flexible cement. If you don’t use the flexible cement, you certainly want to fill it with something. I’d suggest lots of acoustic caulk over foam. It’s at least a lot more dense.

5) I’m not sure what you mean? Weather stripping? If so yes that is probably fine. The Pemko and Zero Int. Stick on gaskets are sound rated and so while I’m sure they don’t work any better than similar stick on gaskets from HD or Lowe’s, you at least have peace of mind on their effectiveness. For what it’s worth I found the larger silicone 3 finger gasket from Pemko to work the best.

I tested my gaskets by turning the theater lights off and lights in the play room on. I then examined for light leaks. I also had my wife put a flash light around the perimeter and again looked for leaks. This process helped me adjust the gaskets and ensure no sound leaks.



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post #18 of 19 Old 10-10-2017, 09:40 PM - Thread Starter
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I've seen conference rooms that had sections of floor to ceiling panels that were on tracks to make smaller spaces. You might get some ideas from a google.


So those are often acoustically sealed. It gave me ideas for making a sliding pocket door that was soundproof. Turns out it’s really expensive. Like when I contacted a manufacturer about this it was in the neighborhood of $5000 for the hardware alone (I would have to supply the wall/door slab).


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post #19 of 19 Old 10-10-2017, 09:45 PM - Thread Starter
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The wife has asked.... about adding a sliding 'barn door' (I blame pintrest). She asked mostly for aesthetics, but has anyone thought about going down that path for creating as a point of soundproofing



Have not researched much on tracks/etc. I could see the possibility of making a larger than the opening by ~8in MDF built up sliding door that would be a double/communicating door to cover a 'standard' door. The thickness could be a design point. Would not have to have the swing stability that a thick heavy door would need. Would be worried about it rattling with heavy bass. Could add a guide at the end to seal it back to the jam/weatherstripping around jam.



Sure it would be an engineering evolution to build, but would solve some issues but likely introduce other issues.


I actually think it would do something. Remember I posted a link to an exterior door with an stc in the 40’s due to a storm door. If adding a store door can add 5-6 stc points I think that a barn door would do something similar.

I think they make gaskets for sliding doors that could be applied to this and it would probably further help with the effect.

You will need to find a low profile door knob so the slide barn door isn’t 4” from the wall (unless you want that but then gaskets again). I would imagine that without a good acoustic deal around the door with a lot of mass behind it that a barn door won’t have the same level of benefit as a communicating door assembly. However I am sure it would do something. I’ve never seen such a test.


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