How much do you want to spend and how much sound do you want to stop? An opening as small as 1/4" between the two rooms will cause the sound to get through. Are aesthetics important? Most sound is stopped using gasketing that can be either surface mounted (cheaper) or concealed in the door. Phil Brady.
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To reduce sound transmission you need one or more air spaces, this reduces the path that sound can travel through. First option is two or three solid core doors where you create an air gap between each. I don't know your room or construction of your space so I can't elaborate on how and where to hang them. I had a hollow core door on the utility closet housing our central AC unit. I replaced it with a solid core plus a fiberglass panel on the back and it reduced the sound enormously. Upgrading the second door to solid core, the hall way door between the utility closet and my listening room removed all noise competing with the music. Sound works the other way around too. Stopping it from going through to the bedroom is the same approach. Gaskets may be required if you have much space under the door and unless the walls are filled with fiberglass sheets like I've done in my room, the door may no longer be the transmission path after upgrade. |
If Albert constructs his "air spaces" with concrete or lead, great! But the only thing that affects (reduces) sound transmission from one space to another is MASS and STIFFNESS, but primarily MASS, not xtra air spaces. I just love the myth that stuffing a stud wall cavity with fiberglas stops sound transmission, LOL! The only thing doing that will stop, are the screams of the little creatures that choke on the fiberglas ;-) As for doors, 1-3/4" solid core (MASS) fully gasketed. with a welded steel frame (STIFFNESS) and no less than 1-1/2 pairs of ball bearing hinges (1-1/2 pair actually = 3 hinges ;-) . |
Nsgarch I think we are agreeing and disagreeing. I agree with your comment on mass and that's why I posted the comment about two doors. However, the space between them is some benefit too, especially if a sound panel is attached. (Hals_den said aesthetics were second to performance). This from Wired Magazine How Sound Travels This from University of Massachusetts, Amherst, MA. Sound attenuation batts soak up sound and can improve the STC rating of a wall. We carefully installed 3-1/2 inch thick sound attenuation batts (Owens Corning http://www.owenscorning.com/ 1-800-438-7465) in all stud cavities after the resilient channel was fastened to the wall. We purchased batts that were sized for steel studs. These larger batts extend into and completely fill the hollow profile of the steel studs. Language on the package claims they can improve partition STC ratings by up to 10 decibels. http://www.owenscorning.com/quietzone/products/products3.asp Specification from Owens Corning including specification of attenuation with acoustical batting and sealing. I agree with your comment about solid core 1-3/4 doors. In fact that's what I used in my home and what I suggested in my post. I also contend two are better than one and better still would be if they did not line up with each other, but rather were staggered. However this is likely not possible in a residence where we have to work with what we have rather than constructing from scratch. |
Albert: the language "Adding loosely packed fiberglass insulation in the wall cavities of interior walls further reduces the energy passing through, in effect making the air between the walls more lossy." is utterly wrong, and contributes to that myth I mentioned. The only way that filling a wall (with anything) can improve the STC Rating(Sound Transmission Coefficient) is by virtue of whatever additional mass it adds to the wall. As such it could be any material: sand, rock wool, lead sheets, wood chips, fiberglas, or even Owens Corning batts ;-), you name it. But the idea of a fuzzy material stuffed INSIDE a wall somehow absorbing sound waves from OUTSIDE the wall is completely bogus. Our acoustics professors at MIT constantly drummed into us to be wary of anyone trying to sell us such drivel (or such products ;-) Here's how it really works: The sound on one side of the wall strikes the wall surface and sets the whole wall assembly moving (vibrating). The now-vibrating surface on the other side of the wall sets the air in the adjoining room in motion, thus acting as a secondary transducer (driver). What's inside the wall doesn't matter a hoot, except insofar as how much it weighs, because the more massive (heavy, dense) the wall's material(s) the harder it is for the initial sound (wave) to set it vibrating. There are some other ways of stopping sound transmission when it's not possible to make the wall itself of high mass, such as hanging a second drywall surface on spring clips in front of the main wall surface. This second surface must be completely sealed with rubber gasket material to the floor sidewalls and ceiling. Sound energy striking this additional "hanging" surface is absorbed (used up) by flexing the clips, and so never even gets to the main wall itself. It sounds complicated but it works, and is used all the time in schoolrooms and music practice rooms. So if any of you feel compelled to stuff your wall with something to reduce sound transmission, here's an idea that not only works, but is easier, in new or old construction, and and probably costs less money: just throw a second layer of drywall on each side of the wall to increase its mass and stiffness. That will reduce the transmission loss to over 40dB (Owens Corning quotes 10dB, but when you really get into their specs, it somehow shrinks to 4dB!) The only way sound absorbing material (called "fuzz" by acoustical engineers) can absorb sound is if it's in the same space as the source of the sound. It can't absorb sound if it's trapped inside a wall cavity. |
There are 2 types of sound transmission, air born and structure born. Air born can be stopped mostly by mass alone. Structure born requires decoupling, which means a mass layer, air gap (or other low density layer), followed by another mass layer. Recording studio doors have mass layers and an air gap. They are usually very thick (3" or better). Albert pointed out doing 2 doors with a significant air gap. This is also done in studios and is called an air lock. It is a greater air gap and thus is even more effective. Last, I'll point out that STCs often quoted for things like this are often useless. STC (sound transmission coefficient) is for 125 Hz. Usually the problem frequencies are much lower, like around 50 Hz and are structure born. Now the door probably is the biggest problem you have, but there's no point in buying a very expensive studio door if your walls are single layer sheetrock and offer little sound isolation. Sound isolation works like the old addage "a chain is only as strong as it's weakest link." Probably the first thing to do is determine what type of sound transmission is the problem and go from there. Here's a linke to our resource page. There is an article we wrote on sound isolation that might be of help. Rives Resource Page |
Thank you all for your helpful respsonses and references. One of the aspects I love about this hobby (or profession for some) is the chance to apply science and test theories in solving problems. I now have some more food for thought, and for a temporary fix for my leaky door I will try hanging my 30 year old Coleman sleeping bag over the door. This will ad some mass and create a 5" air gap. I will post the effectiveness shortly. For a more permanent fix, I'm thinking a heavy exterior door with good seals would be the most economical solution. Can anyone recommend some good manufacturers of such doors? |
I have headphones and use them when I can. However, there are a lot times when headphones are not an option. In any case, I was able to tighten up the door tolerances and temporarily hang two cotton and one wool blanket over the door. I have achieved a considerable improvement in sound attenuation and the Mrs. is surprisingly impressed my blankey solution. It's kind of like entering the yurt when you squeeze through the blankets I see installing a solid core 1 3/4 exterior door with the best weight to price ratio and imploying a good gasket along with stiff framing and hinges as the best solution so far. Then I can see where the next weakest link is. I can't wait. |
Hals_den For a more permanent fix, I'm thinking a heavy exterior door with good seals would be the most economical solution. Can anyone recommend some good manufacturers of such doors? I don't know where you live, but if there's a Home Depot or Lowes nearby they sell several quality levels of solid core doors. I opted for plain (no panel) paint grade since the other interior doors are this style. You can go solid for as cheap as $75.00 or $80.00 (I just checked via internet). Alternately, if you have a builder supply in your area, they stock door and window in an amazing array of styles and finishes, hopefully to suit your home and your wife :^). Often a local handyman will have a wholesale account at one of these places, you can go shop with him and pay him a markup on the door and his labor and everyone comes out great. I did that with my three solid core doors (two different contractors) and got great results both times. |
I would suggest solid core door, not a panel door. Prehung on an exterior frame. Order it without the sill and get a surface mount or recessed automatic door bottom. In addition to the weatherstrip installed in the frame get some surface mounted acoustic seals. Hager hinge makes some stuff at hagerhinge.com . Use 747S or 730S for door bottom and 866 for around frame. This stuff will not be available at home center but is readily available from commercial door suppliers. I used to sell this stuff in another life. Phil Brady. |
Thank you Philbrady . This is exactly the kind of information I am seeking. I appreciate what a great resource Audiogon has become for me. I have learned a lot from this thread and now I can see how mass, stiffness, and air seals all work together to make an effective acoustic door. In the meantime I am tweaking my layered blanket door cover. It's actually quite nice as it gives the bedroom a cozy yurt-like atmospere that my wife, cat, dog, and I all dig. |
