John Sayers' Recording Studio Design Forum Archive

Hey all,

First, let me say thanks for such a great forum. I only wish I had known about it when I started construction.

I have a unique (and probably a bit screwy) situation here. I'm building a mixing room in a storefront loft here in Chicago. I was given a bunch of materials that someone had used to build a portable, modular iso room. This consisted of 20 4' x 8' modules constructed as follows: 3/8" mdf>1/4" neoprene>2x4 frame with fiberglass bat>1/4"neoprene>3/8"plywood (layers are glued to frame so not coupling). I also got a heavy steel door/frame (hung in another 4' x 8'), a lot of sonex-style 2' panels and corner traps, and about 20 square feet of 3/4 neoprene.

I've assembled the wall modules into a room approximately 10' x 15.3' with 9 foot ceiling. (I had to cut up and rebuild a few modules to make it fit, obviously). I'll spare you the details, but I assembled the walls to minimize shorting out the layers with caulk and 1/4" neoprene between the modules. The walls are sitting on top of a continuous layer of 3/4" neoprene between the frames and the existing hardwood floor. My plan was to add a layer of 5/8 drywall RC'd to the inside walls and close off the ceiling with 2 layers of 5/8" drywall (either as one leaf or with a layer of the 3/4 neoprene or carpet pad (that I have) between. Ceiling joists are 2 x 6's, 24" OC, hung from steel joist hangers connected to the top of the module frames so that top of joists is flush with the top of the modules (unfortunately, will couple a bit here). Plan was to lay drywall directly on top of the joists with a layer of neoprene around the perimeter of the top of the modules. Whew.

OK, I now see this design is pretty flawed, but let me say that I don't need a lot of isolation for the control room as I have the building to myself. I'm mostly concerned with having a good acoustic environment to mix in. I would like to have the option of adding additional isolation to the outside in the future and adding a layer of neoprene and wood-flooring. I'm thinking that my goal for this round of construction should be an interior shell of decoupled drywall (walls and ceiling) and hope to gain some absorption from the modules.

So, (finally) my question is:

RC between the drywall and modules? (I think yes)
For the ceiling, joist>rc>drywall>drywall (my vote) or joist>drywall>RC>drywall. Remember, the joists are in steel hangars and only touch the walls through the hangars.

Thanks so much to anyone who takes the time to answer this.

So, essentialy what you have is a rented space, which is a complete outer shell, right? And you have this all to yourself. You have a room-within-a-room built out of these modular building-blocks (which sound pretty cool, by the way) and if you get a good connection between the modules themselves, you've got a pretty tight room. I'd find it hard to believe anyone would make these kinds of modules without making a good system of interlocking them to become air-tight...

The only concern I can see from here is getting heating and cooling into the room. As far as isolation goes, you've got it made as you sit.

If you'll be tracking drums or loud guitar amps outside this little room, in a different part of your rented space, you may need to build another room-within-a-room just to keep neighbors from complaining, but for just mixing it sounds like you have the isolation part taken care of. I wouldn't mess with the modules by adding RC or drywall unless you need more isolation from the rest of your space, which you've said isn't an issue.

What you need to do is treat the inside of that little room so it sounds good. Drywall has little to do with that. Go have a look at http://www.johnlsayers.com/HR/index1.htm and look around this site for other treatment ideas. Since you'll have to treat the room anyway, save the money you'd have spent on drywall for that.

Good luck!
Kase
www.minemusic.net

Thanks for the advice, Kase.

There are some other factors to consider for me, though. Cosmetically, I need the room to look fairly professional and with the neoprene "gaskets" poking out and the silicone caulk I used quite liberally between the module joints (thinking only about the seal and not cosmetics, as I planned to cover with drywall) I don't think I could make it look right without a pretty huge expenditure of time to remove all that material. Secondly, I already bought the drywall - though I could easily use it for the small iso booth I plan to build (properly) soon. And third, I need to cover the ceiling as I don't have enough modules left to do it (it is currently open).

I have some money put aside for the ventilation, but otherwise I'm extremely low on funds as I've just moved to a new city and don't yet have a lot of clients here. The Catch-22 is that I need an operational room to make more money/get more clients. Fun, ain't it?

Thanks again,

Robert

Ok, that clears some of this up.

If the joints aren't pretty, you could put just one layer of drywall over them, but I wouldn't worry about using RC. The modules themselves sound like they have plenty of isolation. Trim off the neoprene and caulk sticking out into the room, and just lay drywall up to it. I'd recommend using very short screws, and placing them so they hit the 3/8" osb and not anything underneath there. Then you can put tape/joint compound over the screw holes and have a nice surface to paint up. You could do the same thing to the outside of the modules, too. My only question here is the strength of the bond between the OSB panels and the structure of the modules underneath... you mentioned that they're glued. If the drywall is setting on the ground, and not relying on the module to hold it up, this won't be too much of an issue, but you should be aware of it, regardless.

Kase
www.minemusic.net

The ceiling part sounded like you had in hand- if the modules can support the weight of it, and I'd think they could if they're built up out of 2x4s. If you have rim joists around the perimeter, you'll have a good tight seal around the room. On the ceiling here, you may or may not want to use RC for some added isolation, but that's up to you- putting 2 layers of drywall on that ceiling, and a deck on top of it, you should have plenty of quiet. For the deck, having one layer of drywall in there is fine, but either over it or under it you should place a layer of OSB just in case you need to move around up on top of it. If the HVAC is coming in from the ceiling (again, I'd recommend this to spare cutting up the modules any more) they'll be happy to have something solid to stand on.

I'm not sure whether the OSB decking would be more effective above or below the drywall... maybe some of the other folks on the board can help with that one.

If your funds for HVAC are limited, you can just put in the duct entrances into the room for the future system, and use it as a transfer system into the rest of the room- put a fan in front of the return duct to pull air out of your control room and fresh air from the room will be drawn into the supply duct. Then later on when you get the money for it, you can finish it off.

Kase has steered you right on this so far - his point of protecting the top, outer layer of drywall on the ceiling joists is a good one - One thing you may run into is span limitations if usint 2x6's - placed on 24" centers, they will span the 10 foot dimension with enough strength to support a total of 5 layers of paneling safely. This assumes an average panel weight of 2 pounds per square foot, or 64 pounds per 4 x 8 sheet. 5/8 drywall weighs about 2.31 pounds per square foot, while 1/2" drywall weighs about 1.68 psf. 5/8 plywood weighs about 1.85 psf.

Your ceiling is OK on hangers, although I would have rested the joists on top of the wall panels. Be careful with thick neoprene, you may end up with worse isolation than without it. Resonance is really tricky to get right.

At this point, assuming you ran your joists the SHORT dimension of 10 feet, I would put a layer of wallboard on top of the joists and then a layer of 5/8 or 3/4 ply. Seal everything, but do NOT glue the layers together. Put R19 insulation in between the joists, put your inner layer of wallboard on the walls after trimming the neoprene (as Kase mentioned), then put your RC at right angles to the ceiling joists, and if necessary you may need to add a joist block at each edge (or a whole new joist) to support the ends of the RC. The general rule is NOT to run the RC closer than 1" from adjoining walls - if your joists are not at least that far from the wall they are parallel to, and not more than 2-3 inches away from the wall, you'll need another support for the ends of the RC.

Mount a layer of 5/8" wallboard (use 12 foot panels for fewer joints) perpendicular to the RC, then the second layer parallel to the RC, using some of the techniques found in the "sticky" called "complete section", keeping everything air tight (joint compound and drywall tape in the field, and acoustic rated caulk around edges)

One clarification - you said,"RC between the drywall and modules? (I think yes)
For the ceiling, joist>rc>drywall>drywall (my vote) or joist>drywall>RC>drywall. Remember, the joists are in steel hangars and only touch the walls through the hangars." -

Your modules are already a double leaf wall system of sorts - if you add drywall, do NOT put RC first or you'll have a triple leaf system and make your isolation WORSE. Same with the ceiling - the RC goes directly on the joists, NOT between layers on the same frame.

I would run your new wall layer clear to the joists, then hang the RC INSIDE the walls and hang the layers of wallboard off the RC. Use spacers and leave a 3/16 to 1/4" gap between the wall and the ceiling wallboard (spacers help here, you can tape them in place temporarily) then, once the ceiling leaf is hung inside the walls, pull the spacers and work foam backer rod into the cracks between wall and ceiling, pushing it back into the crack far enough for a uniform bead of acoustic caulk.

The neoprene in your modules will give some isolation, and putting RC on those walls will worsen things - by hanging the ceiling from RC INSIDE the walls and caulking, you'll further decouple the ceiling from the walls.

If you've somehow run your joists the LONG way of the room, take them down and do it right. The only OTHER safe alternative would be to put joists between them for 12" centers, which will just barely span 15 feet and support 4-5 layers of paneling total... Steve

Thank you Steve for all your input.

My original plan was to finish the ceiling on the outside only with 2x drywall (hence the RC between to create my 2 mass systems) and leave the joists open to preserve more interior volume and so that I could create some easy absorbers between joists. I based my plans on ideas from Alton Hearst's "Small Budget Recording Studio" book and was trying to stay as close as I could to his recommended minimum volume of 1500 cf. With the joists open I'm already down to about 1350 cf. If I close off the insides of the joists I'l lose another 70 c.f. and have to rethink my modal calculations. I've noticed that on this forum you guys don't emphasize that minimum as much as Mr. Hearst.

Bearing in mind that I'm more concerned with the final room acoustics than with isolation (although I'd like as much as I can get), do you think it's a better trade-off to close off the insides of the joists? Also, now that I have looked around this site at the various plans, I'm wondering if I should consider a sloping ceiling, rfz kind of design. I can't splay the walls as I have a door about 5 feet back from the front of the room. I'm probably not going to soffit-mount speakers as I use NS-10's.

Like I said, I wish I had seen this forum before I started construction. Thanks again, guys, for all your help.

Robert

Kase, thanks for your input as well. I'll consider getting some decking on top after I sort out the other details. FWIW, there's only a 3 foot crawl space there below the ceiling in the loft. HVAC will be me, but it would be considerably less than ideal for me to fall through a section of drywall between the joists.

Thanks again,

Robert

Robert, first off Mr. Everest's name isn't Mr. Hearst, although at 90+ years old he may not be surfing this site and so won't complain about it :=)

It's not that we don't think room volume is important, it's more that a lot of our members just don't HAVE the option of larger rooms, building studios into lofts, basements, closets, etc - also, that number isn't an absolute, just a general size below which modes get more cantankerous to smooth out.

If you can find a way to maintain a 2-leaf isolation system and NOT use the inner joist space as part of it, I would do it (especially if the isolation isn't as important) - placing 2-3 inches of absorbent flush with the inside of your joists will open up your room a LOT compared to having solid paneling up there.

In that small a room, splayed walls would be difficult to do and still have enough room to work comfortably - and with NS-10's, soffit mounting is bordering on ridiculous (although it would improve their sound somewhat, it's just that they're kind of small for anything further away than about 4-5 feet) - for placement, however, be sure and check out Barefoot's Wall bounce calculator here -

http://www.johnlsayers.com/phpBB2/viewtopic.php?t=630

For taming reflections, if you can hang a "cloud" over the mix desk and spot treat walls via the "mirror trick", it will help quite a bit. There are other things that can be done to help keep flutter echo from causing problems, I'll get into that if you like but am out of time for the moment... Steve

Thanks again, Steve. Yes, I hope the esteemed Mr. Everest doesn't see that post - I didn't have the book handy and am notoriously bad at remembering names...

OK, drywall directly on the walls to the top of the joists - no RC here. I'm thinking short screws into the MDF and missing the studs. Tape and mud the seams, caulking the corners. Keep a 1/4" gap below the ceiling to fill with acoustic caulk. Now to the ceiling.

My plan for that was to run a 1x4 vertical frame around the outside of the top of the modules with a 2" lip to create a pocket for the ceiling drywall. Then a layer (or 2) of drywall on the joist followed by RC and another layer on that. I'd seal each layer to the 1x4 outer frame. Sound like a plan?

Then I can move on to treating the room. BTW, is there any good use for the acres of 3/4 neoprene I have? I know I can make small iso bumpers for floating floors, but I have enough to cover an entire floor or ceiling. My plan was that if I needed more isolation after the walls and ceiling were up, I could cover the existing hardwood floor with it and then lay
3/4" chipboard right on top. Not the same as correctly loaded floating floor, but it seems like I would gain something over the existing wood floor on joists. The walls were all constructed on strips of the 3/4" neoprene. (I now realize that is not the way to do it, but thats what I have...).

Or should I just sell off the 200 sf of neoprene and spend the money on treatment and the building of my iso booth?

Robert

The gain from floating the floor, but not the walls, would probably not be worth the effort. If these modules were structurally isolated from the floor, it'd probably be a good idea.

Save 'em for when you treat another part of the rental space for a tracking room.

Kase
www.minemusic.net

Hey Kase,

The modules are "floating" on a strip of 3/4" neoprene between the bottom of the modules and the floor. I realize now that I should have worked out the loading to achieve the correct "spring" of 25-75%, but alas, it's already done.

I've been looking into a cheap ventilation solution. Today I found insulated 8 inch flexible ducting (plastic lined instead of metal). I'm thinking that inside a drywall box with a few angles should work pretty well. Might need a plenum. Now I just need to find a cheap, quiet blower of some sort and work out the air exchange/velocity math. I also want to quiet down my Pro Tools rack which I think will be pretty easy.

Thanks for the input.