wall construction question

beardedlurker · Post by **beardedlurker** » Wed Jul 02, 2003 10:59 am

this probably has a fairly obvious answer, but...
i'm getting ready to build a studio. the rooms are on floated floors, and the walls will be built on each independent floor. the walls are going to be 2x6's, with the interiors of each room being constructed of 5/8" sheetrock, 3/4" mdf and 5/8" sheetrock. now my question is: should i finish the exterior of each independent wall, so there is material on each side of each wall, or leave it unfinished and just put the layers on the interiors of each room? man, i wish i had the extra cash to hire someone to design this for me.

knightfly · Post by **knightfly** » Wed Jul 02, 2003 11:49 am

First, for some background (lazy typist here) go to this thread

http://www.homer.com.au/phpBB2/viewtopi ... 86&start=0

and scroll down to the STC chart John posted on Mar 01 - look at the various wall constructions closely, then check the comments I made on Mar 17 as to WHY this is so.

Here are some general guidelines for soundproofing -

1. NEVER waste time/money/materials on construction methods that aren't proven to work, unless you have no life and just like to hurt yourself...

2. The best performance in a sound wall for the money, unless you can afford 3 foot thick concrete, will ALWAYS be a double-leaf wall with only ONE air space. Adding extra walls will usually make things WORSE, not better. (A "leaf" is however many layers of solid material that are layered together on one side of the frame. A standard, interior house partition with drywall on each side of 2x4's is a "double-leaf" wall.

3. This double leaf wall should almost NEVER have exactly the same construction on both sides - a wall transmits sound (bad) more efficiently at its RESONANT frequency. If both leaves of your wall are identical, then so will their resonant frequencies be identical. If that frequency is, say, 44 hZ, then that frequency will pass right through the wall with MUCH less attenuation than other frequencies. Not good.

4. For best performance, there should be no point where the inner and outer leaves of a wall have direct, hard contact with each other. This will allow sounds that impinge on the one leaf to directly vibrate the second leaf, and pfpfpfttt!!! Right on through... The way around this is separate frames, whether wood or steel studs. Drywall on the inside of the inner frame, and on the outside of the outer frame.

5. Things that improve Transmission Loss are: Mass of leaves (more is better, but DIFFERENT is better yet) - Distance between leaves (more is better - at normal wall thicknesses, even an extra inch can help) - Insulation - so far, it appears that 2.5 to 3 Pounds per Cubic Foot is the best overall density for in-wall insulation. This is why USG settled on 2.5 PCF for their Sound Attenuating Fire Blankets - see this link

http://www.usg.com/Design_Solutions/2_3 ... onperf.asp

It's getting close to when I have to go do less fun things, so I'll try to wrap this up for now -

I'd recommend you use steel 6" studs instead of wood if you can - the 20 ga ones can be used for load-bearing walls, and using 6" instead of 4" will improve the TL of your walls.

Put the paneling on ONLY one side of each frame - your goal is to have as much mass in only TWO leaves, placed as far apart as is practical (more air space) with at least 3-4" of either SAFB's (see above) or rockwool or mineral wool (same density) in between. More is generally better if you can afford it, and I believe it may work better (not positive on this) if it actually TOUCHES the inside wall panel - it should contribute to damping the panel, which would decrease the transmission.

On one leaf of the wall, replace the outer 5/8 wall board with 1/2" - on the OTHER leaf, replace the 3/4 MDF with "sound board" - typically 1/2" thick, kind of crumbly - goes by other names such as Homosote, Celotex, etc - it's the stuff those drop-in, 2x4 foot ceiling tiles are made of.

Either find a source locally (commercial insulation/drywall contractors, usually) of REAL acoustic caulk (about $3.50 per 1-QUART tube, or $7.50 each if you have to get it online) and caulk EVERYTHING as you go. You want all construction to be "boat" quality (would float indefinitely, hermetically sealed)

Home Depot carries the 1-quart caulk guns, but don't even slow down at their "wall of caulk" there's nothing there that will help you, except possibly their "drywall adhesive" which can be beaded on wood studs under the FIRST layer to even out irregularities and lessen the chance for rattles, plus it allows you to spread out the fasteners some without losing strength. I don't think it would be as beneficial on steel stud construction though.

One last thing, then I gotta run - check out the SAE site from top to bottom, it's the cheapest "consultant" you can find (free)

http://www.saecollege.de/reference_material/index.html

Click on EVERYTHING - by the time you finish, I guarantee you'll be answering questions for ME... Steve

beardedlurker · Post by **beardedlurker** » Wed Jul 02, 2003 6:20 pm

i'm sorry, i don't want to come across as a dolt, and i think i have. i've been researching building practices for a while, trying to prepare for this, so i do understand about the caulking and floating of floors and switching wall layer materials and all that jazz. i was looking at the sae site, and i found this diagram. is that (loosely) how to build the wall, or do you add additional layers of sheetrock/celotex/etc. to the outside of the walls (facing the space between "studio 1" and "studio 2" in the picture)? that's what's got me stumped, because when i look at diagrams of staggered stud walls, it leads me to think that i should be building staggered stud walls for each room, so that there would be four layers of material between two rooms. am i still being confusing? i'm not a very eloquent typist/speaker.

by the way.. thanks a ton for you very very in-depth post mr. steve.

.mark.

giles117 · Post by **giles117** » Wed Jul 02, 2003 7:39 pm

Bearded. That is loosely how to build a wall.

The additional Materials increase STL. (Sound Transmission Loss)

Yes you do add the add'l materials on the inside of the walls (Studio side or Control Room side respectively) Not in the space denoted as your air cavity. The object is to have as large a cavity as possible between the 2 walls.

Remember, from drywall layer to drywall layer is the area called air cavity in that drawing.

For my set up I have about 11" between walls, not including the insulation space which increases the area to 18"

This was not planned but accidental based on the design of the house I am converting to a studio. My walls are 2 layers of 1/2" Drywall on the control room side, and 2 layers of drywall (1/2" and 5/8" on the Live room wall) I am using R-13 as my insulation

When I say wall, I am speaking of a stud network. So in essence I have 2 walls with material only on the room side of these walls. NOT the air cavity side. Hope that clears it up for you. All additional materials are placed on the MATERIALS side of the wall.

Personally if it were me I'd forgo the MDF and use celotex instead. I built my walls without the MDF and am having great results. I found it to be unnecessary to add that MDF layer.

I can stick my head on the wall, crank my montiors and hear "dead silence" on the other side.

Bryan Giles

jsshop · Post by **jsshop** » Thu Jul 03, 2003 12:19 am

a few questions. you say "Put the paneling on ONLY one side of each frame". So if I am starting from scratch finishing a room that only has 2x4 framing and an outside plywood wall I should not wallboard it, but build a separate inside wall and then wallboard that on the room side right. If I have 2x4 framing would it help to use 2x6 in the inner wall?

Also, what is the best way to frame around a window with a double wall. How do you do that without connecting the walls? If I want a window that I can open and close am I loosing so much that it no longer makes sense to use the double wall?

knightfly · Post by **knightfly** » Thu Jul 03, 2003 11:47 am

"I should not wallboard it, but build a separate inside wall and then wallboard that on the room side " - correct. Filling the cavity with insulation will help isolation by several dB.

"would it help to use 2x6 in the inner wall?" - About the only way 2x6 would help for the inner wall, is that it would increase the stiffness of the inner wall. That would improve LOW frequency performance of the wall somewhat. Otherwise, you can just inset the frame so that the inside edge is in the same place, that will give the same air space between wall panels for slightly less cost of framing materials.

"what is the best way to frame around a window with a double wall. How do you do that without connecting the walls? If I want a window that I can open and close am I loosing so much that it no longer makes sense to use the double wall?" -

The only sensible way to frame a window in a double wall, is to use a double window. (Two separate windows, in two separate, phsycally isolated, walls)

The minute you want a window to OPEN, you lose several dB of isolation. You can get SOME of it back, by using high quality sound-rated windows, but it will NEVER be as good as no window at all, or even a non-opening window. Sliding windows need to be well thought out by the manufacturer or the interfaces will leak sound horribly. Some types of casement windows, where half of the window "cranks open/shut", have fairly good seals and a cam-type lever latch that helps keep them closed tightly. Double-hung (old construction) windows have all kinds of leakage paths, primarily through the counter-weight mechanisms/holes in the casings, etc - If you can find hinged windows with decent seals and put TWO of them, each on their own frame, the inner one opening IN and the outer one opening OUT, you should get a little better isolation than by using sliders.

Generally, opening windows are a difficult problem to solve in a studio unless you're lucky enough to live in the middle of nowhere and don't need sound isolation from the rest of the world... Steve

cfuehrer · Post by **cfuehrer** » Tue Jul 29, 2003 10:05 am

giles117 wrote:forgo the MDF and use celotex instead. I built my walls without the MDF and am having great results. I found it to be unnecessary to add that MDF layer.

Did you sub the Celotex for a layer of drywall? Please explain how you layered you walls for me.

knightfly · Post by **knightfly** » Tue Jul 29, 2003 11:18 am

Just in case Bryan doesn't see this for a while, I'll give it a shot - the normal way is to sandwich the dissimilar layer, either celotex or MDF or possibly particle board, between two layers of sheet rock. This gives an extra "speed change" in the sound's travel to get through the wall. Gypsum has a propagation speed of around 22,000 fps compared to wood's typical 12,000 and air's 1130 fps, so the more changes of velocity the sound has to make the more difficult the path.

If you're looking for max TL at lower frequencies though (like anything below 125 that STC doesn't cover), I'd do at least one leaf of the two with MDF in the middle, celotex in the other. Identical leaves on both sides of the frame cause one particular frequency to hit both resonant points, and that's the frequency you hear on the other side... Steve

cfuehrer · Post by **cfuehrer** » Tue Jul 29, 2003 11:53 am

what I was going to do is 2x4 wall with OC 700 4" in the framing, RC channel, 5/8" drywall, Auralex Sheet Block, 1/2" drywall, primed and painted. Is this good? What could I do (cheaply) to add more STL to it if anything?

knightfly · Post by **knightfly** » Tue Jul 29, 2003 12:05 pm

Carl, that's only part of a wall system - I need to know more about what's (intended)on both sides of the wall, what the wall is separating, what the floor and ceiling are like, and anything else that might "short circuit" your design. You could build a 6 foot thick concrete wall, and if there's a hollow core door in it all you did was make the concrete company richer.

I know that's extreme, but I hate having to explain to people why my ideas didn't work, when they "sorta forgot" to tell me the rest of the place was built out of cardboard boxes.

Anyway, I'm looking at the design you liked on your thread over on John's side - which wall(s) in particular are you wondering about? Steve

cfuehrer · Post by **cfuehrer** » Tue Jul 29, 2003 1:40 pm

Well, the are the insides of the room. The backsides I was not planning finishing off, they would be facing the backside of another wall in a 6" gap. I plan on caulking the seams. The info I was going to use for the walls as I detailed them above is from Auralex. Please, if you have a better way of building a wall, and/or can point me in the direction of information on one (preferably pictures) please do! I am working on a mini construction budget and want to get all the info on the walls, nailed down!

knightfly · Post by **knightfly** » Tue Jul 29, 2003 3:31 pm

Carl, the sheet blok costs almost $3 per square foot - at that price, one sheet of sheet rock would cost $96 instead of $6. While I'm not saying that limp mass is useless, I don't feel it's worth 15 TIMES its weight in sheet rock. The only time I'd even be tempted to pay that kind of price is maybe if I were building a custom door and wanted a dense sandwich material to improve the Transmission Loss without adding much thickness.

I don't have any drawings done yet of the type wall you need, so it may take a while - I'll post back here when I have something. Things have been kind of hectic lately, I'd planned on doing a basic set of detail drawings and keep getting waylaid.

I think you can do a LOT better on cost for wall construction, and still get the kind of isolation you want - it will just take a little time for me to do some homework... Steve

cfuehrer · Post by **cfuehrer** » Tue Jul 29, 2003 4:17 pm

I appreciate the help! I'll check back occasionally. Your design would really help considering my estimate budget costs for the Sheet Block in the entire studio was going to be over $5000!

knightfly · Post by **knightfly** » Tue Jul 29, 2003 6:11 pm

"my estimate budget costs for the Sheet Block in the entire studio was going to be over $5000! " -

Enjoy your new FREE Lexicon reverb... :=)

knightfly · Post by **knightfly** » Tue Jul 29, 2003 7:42 pm

Til I get some drawing done, here's a few -

http://www.usgaction.com/handbook/chap8/chp8toc.htm

http://www.usg.com/Design_Solutions/2_3 ... ictips.asp

http://www.usg.com/Design_Solutions/2_3_12D_system.asp

check out figure 64, that's the framing for any walls where there is glass, so you have individual frames for the glass to be supported separately.

Also, I noticed that USG recommends laminating additional layers rather than screwing them, I had heard different from supposedly qualified acousticians - guess I'll be more careful about info from that quarter...

Gotta run for now, more later... Steve