Inside Out wall frame

Hi John, Which is the correct way to joint 2 wall frames together in a corner...using your idea for insideout walls. Please check the drawing. ABCD or none of the above :D cheers, Luis.

Luis - D is the best system IMO. Check out my attachment. cheers JOhn

Would this type of wall have any STC? or would it just absorb some frequencies?

it has a good STC plus depending on the insulation will absorb down to around 250 hz - AND it's only 5" thick. cheers john

John, the reason I ask because I was looking to build my walls with it. I'll post another question in my original post.

Attached is a drawing of my walls using Jon's inside out design. I just want to be certain I have it correct. At the moment just the external walls are in place and they have been all sealed with caulk (now that's an endless job doing the caulking!) Jon had advised by phone to put up all the ceiling on the channel 1st - this makes it a lot easier - but I want to be certain that I have the top of the internal wall correct because normal construction calls for the top of the walls to be connected to the ceiling joists - but in this situation that isn't possible. The wall guide at the top of the wall is an idea I had - gluing a strip of wood to the ceiling and nailing a strip along the top of the internal wall - total width the same as the wall frame. Then caulk all along it and lift up the wall so the 2 push together to form a good seal & also align the wall. Haven't quite figured out how to handle angled corners but I'll post on that later with a few questions. Thanks!

that's correct Andrew as we disscussed - maybe Luis (LDQ) could fill you in on how he did his. Luis?? cheers john

Cool - thanks John. Just wanted to be absolutely sure I don't screw things up!

that's correct Andrew as we disscussed - maybe Luis (LDQ) could fill you in on how he did his. Luis??

I've been busy the past two weeks so I haven't been surfing lately...any how....I think you have the right idea...some of the differences from the way I did my are: 1. I used 5/8" wallboard for all walls and ceiling. No 1/2" 2. I don't know if it is a good idea to just glue the wallboard on the ceiling since that stuff is pretty heavy. You should be fine using screws...just make sure you dont' short the RC1. 3. In my drum room's celing I did 5/8" 1/2"sound stop (Celotex) and 5/8" since it would be pretty loud in that room. 4. I did a floating floor and not floating walls. 5. Instead of your wallguide I used 1/2" foam. I glued it to the top of the wall with contact cement then once the wall was up in position I sealed it with calking. Check out some pics in the studio under constructions sections (S.Productions). I would think that using the foam there is less transmission from the wall to the celing. I also used metal brackets to joint the walls together... Structurally you shouldn't have any problems...Once you connect 4 of those walls together it won't move anywhere....that is if you could get them up. I needed 4 people to helpe put some of my walls up. Any how hope that helps... Regards, Luis. 5.

Thanks Luis - helps a lot. I was looking at your pics - looks cool. I wondered about putting cellotex inbetween the 2 layers od drywall. Did you crank up the volume in the room yet?

Sorry to butt in here, but this topic is relevant to what I'm working on. Andrew-- What is the advantage to putting the two sheets of drywall on the exterior of the inside wall with the 703 between the studs, then the cloth? Why isn't the drywall on the interior of the wall? I've seen John's "inside-out" wall design mentioned in several posts...where is this described? What's the stc of this design? It's exactly what I was planning on except for the location of those interior two sheets of drywall. Also, if I use steel studs for the interior walls would it make sense to use resilient channel? The steel studs have inherent resiliency so is it un-beneficially redundant to use the rc1? I've been lurking on this board for a while and have learned a ton so far. I just need a few blanks filled in for me...Thanks for any help you could give. Kraig

Hi Kraig, I'm in the same boat as you really - just learming all this stuff. John's inside out design is in the SAE site. The design makes sense although I cannot attest to the STC because I haven't built the wall yet. With the inside out wall - you still have the 2 detached wall masses with a decent size air gap inbetween. The only real difference is you have a smaller air gap - but you save space in the room because you can use the internal of the inside wall for treatment (the 703 + cloth replaces the additional frame you would have to build to hold the treatment). So i'd guess the STC is no worse than a traditional double wall design. John is the best person to confirm. On the RC1 + metal channel - I have no clue really. If you build with the inside out design I'm guessing the rc1 would be redundant. From what I gather the main elements are to make the 2 wall masses as massive as possible + the air space in between.

would having a normal wall (not inside out design) and a separate angled frame inside give more flexibility with absorption, considering that it would give you a variable depth between the wall and the "treatment wall"(assuming you have enough space to play with). I guess with inside out design you're stuck with one depth (the thickness of the stud)...John, Steve...anyone??

Guys, remember that John's inside-out wall was originally a band-aid for situations where there was a need for STC and acoustic treatment without having the proper room for both. The number of studios that have been built with this technique attests to its usefulness - however (it seems there's ALWAYS a "however", doesn't it?) If you are NOT short of room, as in you're building from scratch and not trying to cram Electric Lady Land into a 5' x 7' bedroom with a 6' ceiling, then I'd do things more conventionally (if there is such a thing in acoustics) - the deeper the air space in a mass-spring-mass wall construction (all other things being equal) the softer the "spring"/air space, and the better the wall performance. The more mass in each leaf, the better performance. For this reason I'd only go with inside-out if there wasn't enough room to go with brute force or if I didn't need really good isolation. (I'm sitting here typing this while listening to my neighbor's lawn mower, which is louder from 200' away outside than two computers which are in the room with me - one of the 'puters has 5 hard drives and 7 fans in it, and the case is off, and the lawnmower STILL wins, so guess which way my new facility will go?) About the only thing I'm not settled on for my own outer wall designs is this - what would be the difference in STC between the following - 1. 8" concrete/2 layers wallboard/8" air with rockwool/ 3 layers wallboard or 2. 8" concrete/4 layers wallboard/8" air with rockwool/ 1 layer wallboard? I've yet to see, hear or read what the difference in STC would be - the reason I'm wondering is that too stiff an inner leaf WILL have an effect on the trapping required, so if moving the extra layers from the inner leaf to the outer leaf wouldn't change the STC much, I'll probably do it. Sen, you're right about being stuck with the stud depth on the inside-out way. However, Barefoot brought up the point in one of the acoustics threads about variable depth only working for a slot resonator if you put septums between each slot (or group of slots) , because the wavelength of the affected frequencies is longer than the distance between slats so it averages out. I guess if you had a really long slot absorber that might be less applicable, but you'd be better off asking Thomas about that... Steve

Guys - I don't have any specs on the inside out wall other than having built Left Bank entirely with that system. In fact Left Bank defies theory regarding airlayers etc. The building I started with is a typical 2 storey US barn. 4 x 2 stud frame with and external cladding made up of 6 x 1/2" hardwood laid vertically with 2 x 1/2" battens over the joins. They had warped in the sun so were not airtight, so I disregarded it as a soundproof wall. I clad it internally with a layer of 5/8" drywall and the ceiling was the same except I put it on RC. I didn't bother with the expense of putting any insulation in the outer wall cavity, (did in the ceiling) so the only insulation was on the back of the internal walls in the air cavity as per inside out walls. When it was finished I fired up the genelecs in the control room and turned them flat out. Sounded great BTW, still do, and then went outside to see if I could hear them. Once out of the building they immediately dropped in level and when I was around the corner and down the side they had vanished. I then went to the rear and the client was there chatting with the next door neighbour. I chatted with them and then pointed out that the monitors were at full tilt - they could hear nothing. That was way above my expectation - I expected at least low end getting through. So why?? - I suspect it has to do with the properties of the air gap. In all lab tests the air gap is contained in the structure top and bottom whereas in Left Bank it is open to the whole space above the rooms which is a large airspace because of the angular ceilings. I suspect the sound dissapates into this cavity in preference to going through another mass in the outer drywall, hey but I'm no scientist :lol: :lol: any ideas?? BTW I visited Armirel at Left Bank the other day. He loves the studio and adores the genelecs. He said, "mate , I'm no engineer I'm a muso so I just put mikes over instruments, set levels and hit record. I don't need to eq anything cos everthing sounds great." He was right - he played me some of his jazz sessions and they sounded fine. He's had some of OZ's finest jazz musos through the studio. He's also had clients up from Sydney who have worked most of Sydney's major studios. They bought their own Pro Tools setup and they reckoned it was the best studio they'd worked in, they loved it. We are now talking about a left bank II as he's about to move to a better block of land with better views new house etc. cheers john

Based on the left bank experience - do you think it would make sense to add a layer of drywall on the inside face of the external wall? I was assuming that this would create 3 masses & so be worse. I have wondered if my external wall will have enough mass. Right now it's just 1 layer of OSB covered in polystyrene (which will have no STC value) and then eventually siding. I have been looking for something with mass to increase the mass of the external wall. I've had an idea of putting (& sealing) roofing felt tiles over the OSB on the inside of the extermal wall between the studs. This stuff is remarkably heavy given that it has rock in it & it's dirt cheap - about $10 for one pack that is tough to lift. Does that sound like a winner? It would be easy to staple between the studs & seal it with roofing tar - which is also dirt cheap.

Based on the left bank experience I would add it Andrew........yeah - I know - It's three layers and two air spaces. ;) cheers john

Get a sample of what you intend to use - light up your propane torch and try to burn it. If you succeed, either use something else or take out a $5 million policy with ME as the beneficiary... You could use 5/8" firecode gypsum board in sort of the same way, adding it between framing members and thoroughly caulking. John, I think your assessment of Left Bank's success is correct - that's why I was trying to get Michael to put absorptive stuff around his door from the drum room... Steve

The fire aspect is a good point - I tried the burn test & yes it would heartly support combustion - but heck if the place is going to burn down it's going to burn down no matter what you have in the walls. I plan to have those external walls filled with spray in foam - which is fairly combustible. Covering the external wall with drywall should provide the firestop. One thought about the effectiveness of the inside out wall - could the fact of gluing the insulation to the drywall be one of the contributing beneficial factors? This would allow vibrations in the wall from low end to transfer to the insulation more readily and convert to heat - rather than packed in insulation - which would be vibrated by air instead of the wall itself. Just a theory - bearing in mind that have no clue what I'm talking about :D

"heck if the place is going to burn down it's going to burn down no matter what you have in the walls" - NOT SO. If you use steel studs, firecore wallboard, flame retardent cloth, and concrete shells you can build an almost entirely incombustible shell. And, considering how closed a system you have in a tightly built studio, it SHOULD be as incombustible as you can make it. I might be as non-chalant as several other posters I've answered, except for this: Have you ever seen a marshmallow that spent too much time over the fire? Remember how the black part just sort of "slid off" the gooey insides? Well, I've had the dubious pleasure of seeing that very thing, only with HUMANS - two of them, both of whom lived long enough to scream for someone to kill them. They were both working in a rare metals plant, shoveling metal chips, when something got just a little too hot. The Zirconium chips they were working with are the same metal that is rolled thin and cut in fine slivers to make FLASH BULBS for cameras. Only this "flash bulb" was a room about 20 feet square. It took about 10 years before I could sleep thru the night without nightmares - gee, I wonder why I'm concerned about flammability... Anyway, about the glued on insulation - I don't think so. The conversion to heat is caused by the AIR molecules trying to move back and forth thru the interstices of the insulation and meeting resistance. The more resistance, the more conversion, that's why denser material absorbs more. Sorry about the soapbox - every once in a while I still get flashbacks and it scares the shit out of me. When I'm scared I either go away or blather... Steve

Point well taken about the fire issue - will re-think that addition.

If you're looking for a good wall that's still safe, I'd use two layers of 5/8" firecode sheet rock glued between the studs and up against the outer sheath, as you mentioned - then, if you have the room I'd add 2x2's (drilled, glued and screwed) to each stud on the inside, in order to increase the air space - put 3-4" of Rockwool (3 lb/cu ft is best performance) in between the studs, held in with the SMALL mesh chicken wire available (at least in more rural areas) at farm/home supply places - staple the chicken wire onto the studs being careful to only staple the wire where two strands of wire are twisted together (won't break that way) Then, put Resilient Channel (RC-1) over the stud extensions horizontally on 16" centers (The bottom piece goes on with the "flapping" part UP, so you can screw to it) Add two layers of 5/8 firecode sheet rock, making sure that the rock does NOT touch the floor (use 1/4" spacers while fastening, then pull the spacers and caulk with Silicone or Butyl NON-HARDENING caulk (or US Gypsum's Acoustic Caulk if you're lucky enough to find it) If you want to add a center layer of sound board as well, fine. You will most likely want to put the RC on 12" centers with 3 layers - and be sure to mark floor and ceiling temporarily where the studs are, so you don't "short out" the RC with a screw when installing wall board. When using more than one layer of sheet rock in a wall leaf, do NOT glue the two layers together - performance is better if they can flex independently, as long as they're not separated by an air space. Never line up seams from one layer to the next. Once you have all that in place, you could still put whatever wall treatment you want, wherever you want... Steve

Thanks. I re-tried the burn test & although the stuff melts & flames when the blowtorch is on it - as soon as you take off the blowtorch the flame dies instantly - so perhaps it isn't so combustable or at least no more than the OSB sheathing. The stuff is owens corning mineral loaded felt. It's about half the weight of mass loaded vinyl and only costs $13 per 108sqft roll. For $200 I can put 2 layers between all the studs - so I think it's a winner for adding some mass to the extermal wall. I need to do the double wall construction so I can make the internal layout. So, my wall will be OSB + 2 layers of this heavy felt stuff between the studs (the studs are already well caulked) + foam filled (I'm getting the peaked roof between the roof studs filled with spray in polyurethane foam so the walls is just a bit extra) + 1 layer of drywall Then the 2nd wall - the inside out wall - fiberglass + 2 layers dryrock then the studs. I'm thinking if I can make the external wall as solid as possible (no air) then it'll still only be 2 masses and 1 air gap - which fingers crossed - should work.