Looking for some insight regarding my garage build...

Gotcha, that all makes perfect sense, Stuart, thanks. ...and now, may the hoarding of caulk and Green Glue commence!

I looked up the data sheet for the PL Acousti-Seal and it has a Shore 00 rating of 30-40 which is super super soft. I guess I'll just use it from now on. Man I don't look forward to working with that black goo :-(

After personally having a nightmare with this stuff 14 years ago, my friend experiencing the same thing, I looked into it more and actually found a thread on the forum where this crap ruined someones studio. Don't use it. Greg

Gotcha, Greg, thanks for throwing that out there, bunch of PL around here, almost went that route, but never jumped, thankfully. I've been unable to find something from Home Depot/Lowes, etc, worth committing to. I definitely could use some advice regarding a source for quality, low cost sealant.

...I have another question that keeps coming up in my head; Would using resilient channel on whisper clips allow me to mount my interior leaf on the same framing/studs as the exterior leaf, and still achieve the decoupling benefits that I would achieve by building a new frame on the interior... I realize the air space in between is critical to isolating performance, but I can't help but wonder how measurable the difference is, between the two methods I've described. Any thoughts, ideas, or recommendations? Cheers, and happy Friday!

Would using resilient channel on whisper clips allow me to mount my interior leaf on the same framing/studs as the exterior leaf, and still achieve the decoupling benefits that I would achieve by building a new frame on the interior...

Firstly, resilient channel should not be used on clips: Clips are meant to be used with hat channel, not resilient channel. But even if you could, the answer to your question is "no". You can't get the same results by using any form of mechanical decoupling. You get an improvement, certainly, but you can't get the same final outcome, for the simple reason that the mechanical "spring" and the air "spring" are in parallel: the worse one always subtracts from the performance of the better one. You get maximum performance with the air spring alone: anything you add into that will REDUCE the effectiveness of the air. In simple terms; the air spring is "soft", and the mechanical spring (the rubber in the clips, or the metal forms of the RC) is "hard". Adding hard to soft obviously does not make the total "softer" (which is what you want): it will always make it "harder". A simple analogy: Image that you have clean water in in a glass, and you add some type of colorant to it. No matter what color you add, it will never make the water any more transparent! It's already as transparent as it can possibly be. You can only ever make it LESS transparent. And since the "springiness" of the "S" in the MSM equation is what defines the resonant characteristics of the wall, making the spring "harder" will never improve that. For the same reason, there's a limit to the amount of isolation you can achieve from using clips+hat, or RC, and that limit is about 16 dB greater than what the wall would have achieved without the RC (or clips+hat). You can't get more than that: it is physically impossible, because of the mechanical connection. As rubber and metal technology improve, that might increase slowly to maybe 17 or 18 dB, or whatever, but it can't go much higher than that. On the other hand, with a separate frame, the limits are much higher. Basically, there are no limits of importance for typical home studios: you'll run into other limitations before you run into the limitations of what a good MSM system can achieve. - Stuart -

Great description, as always, Stuart, that was exactly what I was hoping for. ...when I said RC, I was implying hat channel, my mistake...but yes, I assumed the hat/clip approach I mentioned would have a disadvantage against a truly decoupled frame, I just figured it worth asking. Thanks for your response, my friend!

Hey hey! ...so I have finally pre-cut the drywall that I plan to install between the studs of my exterior framing (to beef up the mass of the exterior leaf), and I have stumbled upon some conflicting information; one statement says that I should only apply sealant to the joints of the outermost shell (not in between the drywall and exterior sheathing, for example). I am nearly certain that this is incorrect, as I vaguely recall Stuart mentioning that I should seal the gaps before I GreenGlue my first layer of drywall to the sheathing/siding layer, which as I recall, had something to do with creating a negative pressure that would help the cleats hold up the drywall better, or something like that... So, am I wrong in thinking that I should seal every single gap, before the first layer of Gypsum, and then each and every time that I apply a new layer of drywall, from the outside in, and visa versa?...is the statement relevant that I can green glue the two layers of 5/8", and only then seal the gaps after I have that leaf installed at its full depth? I am about to buy a bunch of OSI SC175, and I know I'll need a lot, but between these methods I've described above, the amount that I'll need will be greatly increased if I do it the way I think I'm supposed to do it, though obviously, I'd rather not piss on a bunch of money for an immeasurable result. Please let me know what you think. Cheers!

I have stumbled upon some conflicting information; one statement says that I should only apply sealant to the joints of the outermost shell (not in between the drywall and exterior sheathing, for example). I am nearly certain that this is incorrect, as I vaguely recall Stuart mentioning that I should seal the gaps before I GreenGlue my first layer of drywall to the sheathing/siding layer, which as I recall, had something to do with creating a negative pressure that would help the cleats hold up the drywall better, or something like that... So, am I wrong in thinking that I should seal every single gap, before the first layer of Gypsum, and then each and every time that I apply a new layer of drywall, from the outside in, and visa versa?...is the statement relevant that I can green glue the two layers of 5/8", and only then seal the gaps after I have that leaf installed at its full depth?

To clear this up, I'll give a convoluted answer: - You just pulled off your vapour barrier and removed the insulation. So now you have your exterior sheating in front of you. Use sealant and go around the perimeter of your stud bay. Also, seal any sheathing joints you see. Basically seal it entirely. Let the first coat dry and apply a second layer of sealant. - Cut your beef up material (in your case, it's drywall) to size. - Lay it down and apply the recommended amount of Green Glue compound to it. - Install the drywall by pressing it against the sheathing and then installing cleats to hold it against the sheathing. - Use sealant to go around the perimeter of this newly installed drywall. It's a good idea to let your sealant dry and apply a second coat. In between coats you can move your cleats so that you ensure that you get sealant around the entire perimeter of the drywall. - Once this second layer of sealant dries, you can repeat the process for adding a second layer of beef up material. The sealant should be strong enough to hold the first layer of beef up material in place while you install your second layer.

I am about to buy a bunch of OSI SC175, and I know I'll need a lot, but between these methods I've described above, the amount that I'll need will be greatly increased if I do it the way I think I'm supposed to do it, though obviously, I'd rather not piss on a bunch of money for an immeasurable result.

Sealing is very important. It's crucial to ensure a good seal. The method I described above will ensure this good seal. Sure, you could just apply one layer of sealant at the end and cross your fingers that it won't fail anywhere. No one is there to stop you from doing that. However, you're already going to great measures to obtain your desired level of transmission loss. Why not go the extra step and know that your build is perfect? Greg

Another great response, Greg, thanks for the clarification. ...and yes, I agree, I'll take the extra step each time, as I'm not looking to throw salt on a weak link. Cheers!

Has anybody used this stuff as sealant?... It dries flexible, that's for sure.

If it doesn't shrink and stays flexible, then it's fine. I'm using DAP Duraflex 230 right now and it works fine. It has horrible reviews for outdoor in the rain, but for my studio build, it's great (and cheap!) Greg

Oh, and be sure to check the date on any silicone product! If it's not applied before the "best before" date, don't use it. Greg

Ok, Greg, thanks for the quick reply, it seems as though this stuff will do the trick. Sweet! ...and the fun begins!

Hello my friends, I hope you're all doing well! I am about to finish the 'beef up' step for the two exterior walls/outer leaves in my live room (garage ground level, beneath my attic control room) and have reached a point where I'm finally beginning to notice some progress, thanks to the Force. With that said, I'm eager to carry on, and again, could use some guidance to help me along my way. Many thanks in advance... Soooo, I have a breaker box in one of my exterior stud bays (outer leaf), which has two separate runs of conduit coming up through the ground, fed from my house, in through the siding/sheathing into the panel. Obviously, those aren't able to be moved, nor can they be truly sealed, so I'm curious what approach I should take at this juncture?...should I just seal it as tight as possible, like everything else I just did, 60 tubes of caulk later. Should I seal/caulk the cleats in too? I am going to continue working on my outer leaf, which will need two more walls (inside the garage) to complete the square; should I fasten these two new interior walls/outer leaves to the other two exterior walls/outer leaves, without any means of decoupling? I'd gamble yes. Would it be ideal for me to make all of the new framing out of 2"x4"s, 24" O.C., and then screw the drywall to it like I would normally?...and if I GreenGlue a second layer of 5/8" gypsum to each new wall, will I do the same and just screw through both layers into the studs, while also being sure to stagger the seams? My attic/control room floor consists of 3/4" tongue & groove ply, with a 1/4" rubber underlayment and 3/4" wood floor nailed in above it; do you think 'beefing up' the ceiling/floor rafters in the same way that I just did my stud bays would offer measurable results, in terms of isolation between my live room and control room?...unfortunately, there are dozens of nail heads sticking through the bottom of the subfloor ply, which will be annoying to remove, assuming that I want to GreenGlue gypsum to it. For what it is worth, you can't really hear foot traffic as it stands, but I do, of course, seek amazing isolation. Should I avoid using insulation with a vapor barrier for my 2 interior/2 exterior walls (inner & outer leaves)?...and how about my ceiling? I'd guess no vapor barrier there, but what do I know? Without getting too complicated, what is a good sized air gap (spring) in between an inner and outer leaf? My sincere appreciation, thanks again for any and all help! CHEERS! -Chris

I am about to finish the 'beef up' step for the two exterior walls/outer leaves in my live room

Good work! I'm still so far from finishing mine :-(

what approach I should take at this juncture?...should I just seal it as tight as possible, like everything else I just did,

Can you build a box around the assembly at which point you can seal it all off?

Should I seal/caulk the cleats in too?

Remove the cleats, seal the part where your cleats were, then apply some caulk to the part of your cleat that touches the drywall and reapply the cleat in a slightly different spot. The reason you put the cleat in a different spot is to allow you to add another layer of caulk to the new spot in case it doesn't seal perfectly and/or the caulk shrinks.

should I fasten these two new interior walls/outer leaves to the other two exterior walls/outer leaves, without any means of decoupling? I'd gamble yes.

Yes.

Would it be ideal for me to make all of the new framing out of 2"x4"s, 24" O.C., and then screw the drywall to it like I would normally?...and if I GreenGlue a second layer of 5/8" gypsum to each new wall, will I do the same and just screw through both layers into the studs, while also being sure to stagger the seams?

Yes.

My attic/control room floor consists of 3/4" tongue & groove ply, with a 1/4" rubber underlayment and 3/4" wood floor nailed in above it; do you think 'beefing up' the ceiling/floor rafters in the same way that I just did my stud bays would offer measurable results, in terms of isolation between my live room and control room?...unfortunately, there are dozens of nail heads sticking through the bottom of the subfloor ply, which will be annoying to remove, assuming that I want to GreenGlue gypsum to it. For what it is worth, you can't really hear foot traffic as it stands, but I do, of course, seek amazing isolation.

I don't have a solid answer for you here. Here is why: - you do have two layers of 3/4" plywood/wood which will roughly match the surface density of your two layers of 5/8" drywall on your walls. - Neither of these are sealed air tight. SO, I'd say at minimum, you have to caulk the hell out of it from below.

Should I avoid using insulation with a vapor barrier for my 2 interior/2 exterior walls (inner & outer leaves)?...and how about my ceiling? I'd guess no vapor barrier there, but what do I know?

Only for your exterior walls assuming I'm understanding your description correctly.

what is a good sized air gap (spring) in between an inner and outer leaf?

Use my calculator to figure that out :wink: viewtopic.php?f=1&t=21770 Greg

Thanks, Greg, you've given me much to consider! ...also, I've been playing around with your TL calculator, that's a sweet tool my friend, well done!...though, I haven't quite figured out how to use it properly, haha. In time... Ok, I'm finally looking to put up some walls soon, but still need to button up some design issues, such as my breaker box, under-stairs door, ceiling mass, hvac, etc. So, I still haven't found a solid answer about when or when not to use an insulation vapor barrier in a two leaf system, when one of the leaves is an exterior wall in the MSM design. In my case, two of my four outer leaf walls are exterior walls, and this is the location making me question my own logic; should I use faceless batts in the two exterior walls/outer leaves, and faced batts on the interior leaves, all around? In regard to air space between leaves, is it undoubtedly best to match the 'spring' depth in each cavity, so they all match as close as possible?...what about the floor (concrete for me)? Basically, I'm curious, if one location offers more airspace between leaves, should I take advantage of it? Thanks!

In regard to air space between leaves, is it undoubtedly best to match the 'spring' depth in each cavity, so they all match as close as possible?...what about the floor (concrete for me)? Basically, I'm curious, if one location offers more airspace between leaves, should I take advantage of it?

It's not the DEPTH that you should be trying to match, so much as the MSM resonant frequency. And that is given by the combination of cavity depth and mass on each leaf. So if you have a smaller gap at some points, then you will need more mass on the leaves to make up for that. And if you have a larger gap, then you could get away with less mass on the leaves at that point. As long as the frequency is low enough, that's fine. And of course, don't forget that the cavity does need to be filled with insulation, no matter how small or large the gap. It is best to not leave empty airspace in the cavity, if you can avoid it. - Stuart -

...ahhhhh, I seee, so then it seems that I have visualized the insulating step all wrong, as I imagined two insulated leaves (insulation stapled to each respective frame) with an airspace in between. With the above statement in mind, if I have a 16" air gap between leaves, how in the hell should I fill that entire air cavity with insulation, as there aren't batts that large !?

if I have a 16" air gap between leaves,

That sort of begs the question: Why would you need / want 16" between leaves? :shock: That sounds like you are wasting 12" that could have been on the OTHER side of the leaf, inside the room.... I'm trying to imagine a situation where you would need to leave 16" between leaves.... - Stuart -

With the above statement in mind, if I have a 16" air gap between leaves, how in the hell should I fill that entire air cavity with insulation, as there aren't batts that large !?

As an example, you could use 5 1/2" thick pink or white fluffy fibreglass insulation batts and put 3 of them in. That would give you a bit of compressed insulation which isn't great, but it would be minimal. If you're feeling energetic, you could rip 10% off of the 3rd one. Greg

That sort of begs the question: Why would you need / want 16" between leaves? :shock: That sounds like you are wasting 12" that could have been on the OTHER side of the leaf, inside the room.... I'm trying to imagine a situation where you would need to leave 16" between leaves....

I'll have 16" between my subfloor above and my inside out ceiling modules. Over 600 ft2 means it's going to cost me a small fortune to buy the insulation. Jan 2nd prices go up another 8% so I better buy a butt load before then! Greg

Ahhhh! That makes sense. I was think we were talking about walls, not ceilings... So your joists are 16"... Hmmmm... tough call.... The main purpose of the insulation n the cavity is to damp all of the many resonances going on inside there, not just the MSM resonance. There are other things going on too, such as standing waves forming down the length of the cavity and across the cavity. It would be good to have damping on all of that. Another issue is that the insulation slows down the speed of sound (or stated better "sound travels slower in insulation than it does in free air"...), so putting in lots of insulation makes the cavity appear "bigger" to the sound waves, thus lowering your MSM frequency... but with 16", it's already pretty low! And one more issue is that the insulation changes the way air deals with heat from adiabatic to isothermal, which you could say is more effective... While on the other hand, 16" is a whole load of space to fill with insulation! :shock: Perhaps a reasonable compromise is to have something like 4" at the top of the cavity (up against the subfloor above you), a similar amount resting on your inside-out ceiling, and occasional "chunks" distributed around the rest of the cavity. In other words, something like a piece of 4" 703 standing up vertically on edge across the joist bay, covering the rest of the 16" between the joists, every few feet along each joist bay. I don't have any research to base that on, nor equations to tell you how well it would work, or how far apart you could space those: It's just a reasonable assumption, as it would damp the other resonances reasonably well... - Stuart -

Perhaps a reasonable compromise is to have something like 4" at the top of the cavity (up against the subfloor above you), a similar amount resting on your inside-out ceiling, and occasional "chunks" distributed around the rest of the cavity. In other words, something like a piece of 4" 703 standing up vertically on edge across the joist bay, covering the rest of the 16" between the joists, every few feet along each joist bay. I don't have any research to base that on, nor equations to tell you how well it would work, or how far apart you could space those: It's just a reasonable assumption, as it would damp the other resonances reasonably well...

That could save a lot of money but would complicate the build. Trying to get the insulation anchored to the subfloor would be time consuming. This picture shows the great benefits of insulation in the cavity! Greg

Soundman2020 wrote:

if I have a 16" air gap between leaves,

That sort of begs the question: Why would you need / want 16" between leaves? :shock: That sounds like you are wasting 12" that could have been on the OTHER side of the leaf, inside the room.... I'm trying to imagine a situation where you would need to leave 16" between leaves.... - Stuart -

...see Greg's reply below. :D ..haha, precisely why I was asking about different air depths in between leaves, considering the depth of my ceiling joists vs. the depth that I'm going to need for my walls, which are hopefully NOT 16"! :shock: ...sounds like a new California pollution campaign; Proposition NOT 16!!! I digress.

Gregwor wrote:

I'll have 16" between my subfloor above and my inside out ceiling modules. Over 600 ft2 means it's going to cost me a small fortune to buy the insulation. Jan 2nd prices go up another 8% so I better buy a butt load before then! Greg

Soundman2020 wrote:

Ahhhh! That makes sense. I was think we were talking about walls, not ceilings... So your joists are 16"... Hmmmm... tough call.... The main purpose of the insulation n the cavity is to damp all of the many resonances going on inside there, not just the MSM resonance. There are other things going on too, such as standing waves forming down the length of the cavity and across the cavity. It would be good to have damping on all of that. Another issue is that the insulation slows down the speed of sound (or stated better "sound travels slower in insulation than it does in free air"...), so putting in lots of insulation makes the cavity appear "bigger" to the sound waves, thus lowering your MSM frequency... but with 16", it's already pretty low! And one more issue is that the insulation changes the way air deals with heat from adiabatic to isothermal, which you could say is more effective... While on the other hand, 16" is a whole load of space to fill with insulation! :shock: Perhaps a reasonable compromise is to have something like 4" at the top of the cavity (up against the subfloor above you), a similar amount resting on your inside-out ceiling, and occasional "chunks" distributed around the rest of the cavity. In other words, something like a piece of 4" 703 standing up vertically on edge across the joist bay, covering the rest of the 16" between the joists, every few feet along each joist bay. I don't have any research to base that on, nor equations to tell you how well it would work, or how far apart you could space those: It's just a reasonable assumption, as it would damp the other resonances reasonably well... - Stuart -

Insulation. Yay. It's funny, every time that I start feeling like I'm making progress, the weight of every small decision I make seems to make me feel like an immensely top heavy drunk. :shot:

shows the great benefits of insulation in the cavity!

Yup! :thu: Sometimes people don't realize how important it is, or what it is really doing. The overall difference in isolation for a typical wall can be as much as 16 dB, when comparing "empty cavity" with "full cavity fill". It's the single biggest thing you can do to a wall to get a major difference in isolation. Adding an extra layer of drywall will get you a few dB, increasing the cavity depth will get you a few dB, increasing the stud spacing will get you a couple of dB... but putting insulation in there will get you at least ten dB, and maybe 16 dB (or more, under some circumstances).

It's funny, every time that I start feeling like I'm making progress, the weight of every small decision I make seems to make me feel like an immensely top heavy drunk.

Isn't acoustic design FUN! It's amazing then things you learn.... Now everybody knows that if you want to feel like an immensely top heavy drunk, all you have to do is to try to design a studio! :) :shot: On a more serious note: it's a huge subject, and there's always more stuff to learn. It's a moving target, too: just when you think you are getting a good handle on things, some darn scientist goes and publishes a new research paper, or writes a new book! Sigh.... - Stuart -