double interior sound wall with a twist

Looked at many of the threads and links on sound”proofing” interior walls found through the “search”. Good stuff.
Wanted to see what the community thought about a different approach to a double wall for sound attenuation purposes (bedrooms, library, utility rooms).
Was thinking of ripping 2×4’s in half to make two complimentary base (and top, of course) plates. Then using studs twisted so flat sides face room (please, no cussing…) putting them on 24″ centers (they are all nonbearing walls). The two plates would be separated by a 1″ gap with the studs on one side offset from the other side by 12″. Was thinking of sandwiching a 1″ foam board between the two split wall plates thereby leaving about a 3/16″ hypothetical (although not perfect in practice, i realize) space between backs of all studs and the foam board. One wall would be covered with 5/8″ drywall while the other with 1/2″ with accoustical caulk in joints. Final wall finishing on both walls is to be 3/4″ T&G pine or oak siding. Outlets would be can-foamed where they penetrated the foam board. Was also hoping that a ripped 2×6 second top plate to tie the two halves would not wreck the sound benefits unduly. Was also hoping that the DW/wood siding combo would be stiff enough to make up for the studs not being on edge. Was undecided by the links/discussions whether foam board would be ok or if any sandwich material should be used at all. And, should acoustical glue be used between drywall and siding?
Any insights would be appreciated.
Replies
Sounds like too much work.
Set 2x6 sills and plates and the stagger 2x4s, front/ back.(Front 8" from end then 24", 16"OC etc..) (Back, start at corner, 16"OC). Then weave batts between the 2x4s which are fromt, and back every 8"s. More the merrier for the insulation. No sound will pass through the wall.
Hey, presto.
Well, very little sound.
skipj
Edited 12/10/2007 2:19 am ET by skipj
You are re-inventing the wheel.
Typical detail is to use a 2x6 plate top and botom, then use 2x4 studs staged so they do not tounch to transfer sound vibrations.
In commercial where you do fully build double wall similar to yours, it is full 2x4 but instead of foam between, it is gypsum board. The heavy mass absorbs sound better. You use soft sound dampening material on the side of wall originating the sound, not inside the wall.
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Like the others write, the 2x6 with staggered 2x4's is standard but flat studs would also support the finish. Sound batts are better than foam board. If you really need the sound separation, put 2 layers of 5/8 rock on one of the sides for density and better yet, separate those 2 layers with resilient channel (looks like z furring). Filling the gaps is important too. Also, be sure the ceiling or floor isn't a sound transfer point with ducts etc.
Norse
If you do it that way, be sure to pick perfect studs.
Perfect studs also known as steel studs. And make sure you glue put a dab of glue between the z channel and the stud as well as the gyp and the channel. You'd hate to go through all that work and get a buzz at some frequency in your home theater.
Mass is key. Forget the foam board it won't do anything. Do a google search for: STC wall assemblies
Thanks, guys. I knew that it was a departure from standard practices and that the community would have good food for thought on the subject. Thanks, again....
I'll second everyone's comments that you're making this too hard. :-)
Piffin suggested using gypsum in the middle, if expense really isn't an issue, try using Durock instead. It's more dense than gypsum so you'll see an improvement in the STC.
Since you're going to this extent, have you examined the other 2 planes in the room? ie. floor and ceiling? Are you putting something in place to block noise transmission in those directions?
Glen
Ceiling shouldn't be a problem -- attic above with blown cellulose.
Floor, however, is another question in itself. The basement will be finished (eventually) so kinda wanted to lessen footfall some. Was thinking of using something like the 5/16" Acoustipad from SoundSense on subfloor with laminate flooring on that. Subfloor is on floor trusses so was thinking of using resilient channels (RC-2) across those before putting up basement ceiling (T&G pine). Have no experience with Acoustipad, though, so don't know if it's ok to use with laminate... more research, i guess.
California (of course) publishes an STC assembly rating comparison manual. The best STC in that book comes from two 2x4 walls one inch apart staggered studs with 3 1/2" insulation and a one inch air gap between the studs. Not a whole lot of diff between 1/2" rock and 5/8 but you need to be obsessive on the caulking of the bottom plates and penetrations. Adding material between the studs or filling the space full of insulation does not perform better than the one inch air gap.
I loaned my copy out and it never came back or I could give references.
I made a sound proof phone booth this way in my powder room at my last office. If I had a really tense conversation I would go in there and talk to the individual while watching my own face in the mirror over the sink. If my face looked angry or anxious it generally was noticeable on the other end of the line. If people in the office were noisy I could just step into the powder room and shut the door.
I originally built it to give people privacy while using the toilet but a sound proof room is a very handy thing to have.
m
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"You cannot work hard enough to make up for a sloppy estimate."
Yeah, i saw the wall you mentioned in one of the links, but i wanted to keep the wall footprint as small as possible. The system i described would be about 7 1/8" whereas the better wall (as you described it and with the siding as well as rock) winds up closer to 10 5/8". Maybe i shouldn't be worrying about the extra 3 1/2" tho....
In some plans 3 1/2" may as well be a mile, in some it's no big deal. Where I've been concerned about sound it's usually a music room or home theater or a privacy issue in a powder room or office so generally an indoor to indoor issue. For exterior walls maybe spray foam would be worth considering.m------------------
"You cannot work hard enough to make up for a sloppy estimate."
I don't think exterior walls will be a problem as they are ICFs, but it's the back to back bedrooms connected to home office connected to TV family room that raised my design concerns. Maybe i'm too concerned over bedroom privacy and TV room isolation....
Thanks again for all the info.
In addition to what others have said consider using this:
http://www.jm.com/insulation/faqs/996.htm
And here is some more info for you:
http://www.soundproofing.org/infopages/channel.htm
Lol. Thanks for the laughs as well as the links. Had already checked out the second one. Good stuff.
this topic has been toosed around here alot... and i think sound proofing walls/rooms is alot like fast cars... speed cost... how fast do you want to go...
but attention to detail will get you alot in the form of less sound transmission...
the main idea is the 'seperate' or break the path of the sound.... air gaps very small holes... gaps under/around doors these are places sound as direct access...
junction boxes i glue a 4x4" scrap of drywall onto the back of each...
i hang one side of a wall that gets drywall on both sides... then seal it from the non hung side... looking for light.... a few quart tubes of any liquid nail type product works for me... i then glue as much scrap drywall to the back of the hung drywall as i have... even a 10" sq piece will change the way sound travels thru the wall... plus it gets rid of all your scrap drywall... i also spray foam every drilled wire or plumbing hole... i run a bead of caulk where the plate meets the floor... while i'm glue'n scraps of drywall to the backside of the hung wall... i make a point to cover the back of all joints...
I did see once where a guy built 2x6 stud walls but put a saw cut up the center of each stud leave'n the top, bottom and maybe 2other places in a 12ft wall uncut... on the center uncut places he off set another cut... his idea was to "uncouple" the 2 sides of the stud... I know at one time they made a metal stud with a rubber center web with the same idea in mind...
they make a wall board glue... where you glue every stud... screw it off let the glue set and then remove the screws... that is supposed to help...
fiberglass anything... sound batts ect... do all but nothing...... mass and decoupling and sealing all paths... seems to be the most cost effective... i guess if you wanted to fill each stud bay with sand... it might work...
just my 2 cents
p
Hey, interesting stuff. Thanx. More to ponder. ;)
This is probably pretty extreme, but a couple miles from my house is the quietest place on earth as recognized by the Guiness book of world records....
It's a place called Orfield Laboratories; it used to be Sound 80 Studios, where Bob Dylan recorded Blood on the Tracks. They've measured the sound level inside their anechoic chamber at negative 9.4db!
Here's a description of the place:
http://musicalperceptions.blogspot.com/2005/03/quietest-place-on-planet.html
There are a few pictures here:
http://minnesota.publicradio.org/display/web/2006/07/27/_orfieldlaboratories/
Making up a sound assembly by adding together lots of sound absorbing materials often leads to unpredictable results. For instance, adding mass such as the durock or gypsum in between the two stud walls which would seem like a good idea, actually reduces the STC rating and is rarely included in most wall assemblies these days.
Your best bet is to Google wall assemblies until you find one that fits your situation. There are several that use a single 2x4 stud wall that have tested at an STC of over 60, which is a very quiet wall.
If you use a tested assembly and install it diligently you can guarantee results. It's like using a recipe when cooking.