SOUNDBOARD + 5/8" SHEETROCK

[luvshinerbock]

You guys are so helpful I just had to post another inquiry...after much reading/searching on this site I found myself bogged down by the massive amount of information regarding wall construction. Before finding this site I had purchased 5/8" drywall and 1/2" soundboard (which was recommended to me by several people in the construction business). Now I've read up on Thermafiber SAFB and intend to fill my walls with that.

However, and here is the actual question, I am wondering what is the best method of erecting the walls using the materials I already have. Should I screw the drywall to the wood studs and glue the soundboard to the drywall or vice-versa? (I don't think adding a resilient channel is cost effective for me, as this is strictly a project-demo studio that will be used mostly for producing my own music. The space is rented and I don't want to go hog-wild on construction costs). Worst-case scenario is needing to add an additional layer of sheetrock. If I understand the posts so far, I need to screw one layer to the wood studs, then glue(using joint compound)/screw second layer to the first, but not to the studs. Which material would you put up first?

THANKS for your feedback!

[knightfly]

It's not recommended to use Laminating (Type G) screws with sound board - it's just too soft to hold well. By the same token, putting the sound board on the OUTSIDE will screw up the absorption coefficient of the wall - most sound board has little absorption at low freq, and a peak around 2 kHz- that's hard to compensate for, so the best way is to bury it under sheet rock.

Screwing two layers onto the same studs, as you mentioned, lessens isolation quite a bit. Even more if the studs aren't staggered.

Which brings me to a possible solution - Can you afford maybe 20-30 dollars more, and to lose 2" of floor space? If so, I'd build a staggered stud wall and weave heavy spun fiberglas insulation between the studs, screwing the sound board directly onto the studs (preferably only on ONE side) and then putting the second layer of gypsum on using fewer screws, and construction adhesive (only in stripes in line with the studs) - This will minimise the flanking caused by using thru fasteners on the second layer (as will staggered studs) and still allow the panels to vibrate independently, which is also better for sound isolation.

Here's a picture of the type frame I'm talking about - You use 2x6's for bottom and top plates, and 2x4's for studs. Each side of the frame has 2x4's on 24" centers, with the opposite side offset 12". The construction as shown, if you use all 5/8" sheet rock, is good for about STC 54. With soundboard on only one side UNDER the sheet rock, probably about the same. If you do both sides the SAME way, it will be WORSE. That's why I'd only do the soundboard under ONE side. Different resonant freq's give better sound control.

From what you've told me so far, that's the best way to get what you need at least cost... Steve

[luvshinerbock]

Thanks again for the timely reply...the good news is that I heard about this method before. The bad news is that I had already put up the framing for the walls using standard 2 x 4's for the footers/headers with the studs placed 16"OC. Mmm...dilemma. One part of me just wants to get the darn walls up and get rollin', the other part wants to try to get it as good as it can be (with my limited resources).

The soundboard placed on both sides will actually be worse?! Wow-never would have guessed. Sheesh-I wish I woulda found this site long ago! "Woulda, shoulda, coulda..."

How about putting 1/2" sheetrock on one side instead of the soundboard (along with the 5/8"??)...so, 5/8" + soundboard on wall (filled with Thermafiber) then 1/2" + 5/8?"

Thanks again for all your great help Steve!

[knightfly]

What you do now depends on your priorities mainly - for one thing, normally sound walls are constructed on 24" centers because it lets the wallboard flex a little more, which absorbs more sound. However, for LOW frequencies there are slightly different rules, and STIFFNESS is a virtue. The downside of this is; the higher freq's will pass through a stiffer partition easer, so you win and you lose.

There are a number of ways you can go from here -

1. if you can spare an extra 2-3" of thickness in the walls, I'd put the 1/2" gypsum/1/2" soundboard/1/2" gypsum sandwich on ONE side of your 16" center frame, using the offset glue/laminating screw method of fastening for all but the base layer - then, you can rip 2" wide plates/caps and graft them onto the existing plates/caps, and putting staggered studs on this new side as follows: put the first new stud (all new studs even with the edge of the ADDED plate/caps) exactly 4" (leading edge-to-leading edge, or center to center) along the frame from the first stud on the OLD side (this will leave an air gap between the old and new stud of 2-1/2") - Then, put all the rest of the new side's studs on 24" centers. They will ALL miss the old studs with a 2.5" air gap on one side or the other. This will (barely) leave room for 3-1/2" spun fiberglas insulation, woven between studs as the above picture. Now, on the NEW side, you can put two layers of 5/8" sheet rock (gypsum wallboard) - for ALL panels, make sure you thoroughly caulk with acoustic sealant (commercial drywall contractors are best bet for getting this, some are helpful - others, well...)

Doing it this way gives you a stiff leaf (16" centers) and a looser leaf (24" centers) dissimilar paneling (1/2" gyp with soundboard between on one side, 5/8" double gypboard on other) the stiff side helps low end, so the bottom 2-3 octaves of music that aren't even considered by STC ratings will be blocked better this way. The 24" center half will take care of the rest of the frequency range. If you use wood studs this way, You will also want to use the offset strip glue and laminating screws for the second layer of 5/8" wallboard on the new (staggered) side. NOT doing this will cost you most of what you gained by staggering the studs.

The other alternative would be to put Resilient Channel on the second side, and fasten both layers of wallboard to the channel (ONLY!!) This is explained here

http://johnlsayers.com/phpBB2/viewtopic.php?t=503

Be sure and download the USG manual - it's a lot, but very useful info.

Here's a couple of threads that discuss some of the construction methods -

http://johnlsayers.com/phpBB2/viewtopic.php?t=598

Actually, that one is the main one from here - this is a page that does a pretty good job of showing what's responsible for sound isolation -

http://www.domesticsoundproofing.co.uk/tloss.htm

Yet another way to get as good results - you could get some of the thin, 1-5/8" steel studs and build a second frame spaced away from the first (16" centered one) by maybe an inch - set the studs in the same places as I explained above, offset from the first one and on 24" centers, and put your two layers of 5/8 rock directly on them, no glue, no Resilient Channel, just lots of acoustic caulk (sealant) - should be about the same or better.

Here are some comparison STC values so you can get an idea of what's better than what - keep in mind, though, that these completely ignore anything below 125 hZ (that's what STC curves are, between 125 and 4k, with the dB # based on what's happening at 500 hZ)

http://www.saecollege.de/reference_mate ... 0Chart.htm

Note that your existing construction is (sorta) shown there, except it's based on 24" centers. I'd REALLY recommend you either tear that out or add a "softer side" like I described -

Gotta go for now, happy reading - let me know which (if any) way you decide to go... Steve