Rogue wall using SIPs

Aaberg · Post by **Aaberg** » Tue Jul 27, 2004 4:20 am

I'm building a studio using Structural Insulated Panels and a grain bin over a concrete slab. Everything's going great, but one of the SIP walls actually amplifies outside sound. None of the other walls do that, and I'm pretty stumped as to why, although I have theories. I'm planning to add mass to that wall using Auralex Sheet Block on the SIP, with sheetrock over that, then with another layer of sheetrock suspended on resilient channel. Any ideas? Thanks.

knightfly · Post by **knightfly** » Tue Jul 27, 2004 8:43 am

If you use only about 1/2" air space such as with resilient channel between layers of wallboard, a single layer of wallboard on one side of the channel will set up a resonance at around 200 hZ due to mass-air-mass resonance - if you just add mass to your SIP's you will lower the resonant frequency, which may be all you need to do - however, you probably won't have a lot of isolation that way because there isn't an air space or a second mass to complement the first one.

You can find out what the resonance of your SIP is by merely "playing" it with something like a Tympani mallet and listening - if it's close to any sounds you're trying to exclude, there's your answer (resonance) - any wall is weakest at its resonant frequency.

Is the problem SIP mounted any differently, or a different size, or is there a sound source on that side that's not directly striking any of the other panels?

That's about all I can think of at the moment... Steve

Aaberg · Post by **Aaberg** » Tue Jul 27, 2004 9:00 am

Thanks, Steve. That's kind of the direction I was headed. There IS a heat exchanger on the other side of the wall about 30 feet away, and I can play the wall so that a frequency pretty close to that emerges. I'm going to try mass-loaded vinyl and sheetrock and see what happens.

Aaberg · Post by **Aaberg** » Tue Aug 03, 2004 6:20 am

Just a note to anyone trying to make a studio with Structural Insulated Panels: they're great for thermal insulation, bad for sound. After reading all the topics in the forum (thanks a million, guys!) it's quite obvious that SIPs are essentially a highly resonant single leaf! The foam between the particle board apparently doesn't stifle any resonance...in fact, there are certain frequencies that are amplified by the SIPs! Right now, I'm experimenting with the cheapest materials possible to try and mass load one side of the SIP...gypsum board layers. I'll let you know how it goes.
In the meantime, if anyone has any experience with this, I'd love to hear from you.
My plan right now is to use 2 layers of sheetrock on the inside, acoustic caulk the heck out of it, then put a resilient channel on the outside with on layer of exterior gypsum. My thinking is that if I change the mass of the 2 sides to different values and add at least a little bit of air space, it should work. Any thoughts?
Thanks.

knightfly · Post by **knightfly** » Tue Aug 03, 2004 7:58 pm

Might be OK as long as you don't have something like a Steiger Bearcat pulling a 10-bottom roll-over close by(or a train crossing) - with that narrow an air gap, your low frequency isolation is gonna BLOW... Steve

Aaberg · Post by **Aaberg** » Wed Aug 04, 2004 1:14 am

Steve,
Yup. That IS a worry. One thing I thought of doing, since I have a roof overhang, is building airspace on the OUTSIDE of the wall. I'll go back and read the Stickies, but is there an optimum airspace for attenuating low frequencies? Could I do it by building with 2X6 studs, isolating them from the wall with rubber strips, filling the airspace with 703 (or is it better with nothing), and floating some exterior gypsum with RCs? Then I'd have to figure out how to mount the siding.
This is a wonderful website and service you guys are doing. Can we contribute with a check?
All the best,
Phil

Aaberg · Post by **Aaberg** » Wed Aug 11, 2004 9:12 am

That wall now consists of the SIP with 2 layers of sheetrock on the inside, sealed with Silicone II. It's made a lot of difference, but I'm considering installing an exterior wall to add some air space (I have room to do that and it's not too awkward because of the SIP construction.)
I've never talked to anyone using SIPs for a studio, so I really don't know whether you can consider a SIP a one or two leaf construction.
If it IS a one-leaf construction, then adding an air space would be good, right? I need some help here my brothers and sisters.

knightfly · Post by **knightfly** » Thu Aug 12, 2004 6:03 am

SIP's are normally a single leaf, since the sandwich material isn't usually open-celled - still, the mass is minimal so they won't do as much as a heavier material. Good news is they shouldn't work poorly because they violate the 2-leaf rule, they work poorly because they have low mass

Steve

Aaberg · Post by **Aaberg** » Fri Aug 13, 2004 12:56 pm

Thanks, Steve. I'm getting closer. Looking for some external gypsum board (a supplier told me there actually IS such a thing) to add more mass to the wall without taking away from my meager control room space of 14X13...it's a one-man studio and I usually work alone, so it's not a big deprivation. Then, we were thinking of adding something called "concrete board siding" on top of the external sheet rock.
Do you think putting in a layer or two of EPDM would help?
Thanks.

Aaberg · Post by **Aaberg** » Sun Sep 05, 2004 1:04 pm

Well, people around here (remote Montana) have HEARD of external gypsum board, as is "Waaalll, there was a fella over near Froid who used some on his barn once. Doknow where he found it though."
What I'm trying to do is add mass to the outside of one of these SIPs, since I don't want to impinge on the internal space anymore.
A SIP is a "Structural Insulated Panel", meaning there is no framing, other than on top and bottom of the panels. The panels are constructed of a 1/4" of particle board on each side of a 9" slab of rigid foam. I have 2 layers of 5/8 sheetrock on the internal wall that's causing the problem. It's helped a bit, but I still need more isolation, and there's a particularly annoying resonant frequency in that wall. I figure if I can add a LOT of mass on the external wall of the SIP, it should help.
Anyone have any ideas for commonly found materials to add a lot of mass to the outside of a wall? I don't have to worry about how thick it is, so I'd rather not order that super-expensive "mass loaded vinyl". I'd also rather not pay exhorbitant freight charges here. There's a Home Depot 100 miles away, so I could do that. I'm also close to Lethbridge, Alberta, so that's a possibility.
Any help is greatly appreciated. Picture below.
Best,
Phil

knightfly · Post by **knightfly** » Tue Sep 07, 2004 12:48 am

I think that of all the options you've suggested, doing a separate outside frame with more mass makes the most sense - if you do this, you will need to completely fill the air gap with insulation, and fairly tightly packed at that - this is the only way I know that you might be able to damp those pesky resonances in the panels. Right now, they are being allowed to play their favorite note with little or no damping.

One way to find out if my above comments will work - while the wall is doing its obnoxious thing, place a hand firmly in the center of the panel - if it helps, then my suggestion should work pretty well. The outer mass will help TL, and the insulation will help damp the inner panels to kill the resonance.

If you do this, and have a separate frame outside, don't use RC - it's not just unnecessary, but will lower the low freq TL slightly. Besides, you already have a springy enough wall with the SIP -

One other thing that may work - if you have access to a place that does sprayed cellulose insulation, you might try spraying a couple inches onto the outside of the SIP before adding the 2x6 frame and at least two layers of mass (but only one leaf, no air between layers) - these layers can also be OSB, it's more expensive but better suited to outside use - it's just a little bit lighter than gypsum so two layers of 5/8 would work about like two layers of 1/2" gypsum, possibly a little better.

Keep in mind that for isolation, this outer leaf needs to be continuous with the outer leaf of your containment ceiling, and the inner leaf needs to be continuous with the inner ceiling mass... Steve

Aaberg · Post by **Aaberg** » Tue Sep 07, 2004 5:30 am

Steve, thanks. More to think about. Each addition of gypsum on the inner wall helped the problem, so would adding more layers without a frame on the outside be a solution? I ask because of this quote:
"Keep in mind that for isolation, this outer leaf needs to be continuous with the outer leaf of your containment ceiling, and the inner leaf needs to be continuous with the inner ceiling mass... "

Tell me if I've got what "continuous with the outer leaf of your containment ceiling" means. The ceiling is a 10" thick SIP (oddly enough, there's very little if any sound coming through it) covered by mastic, then covered by several layers of EBDM rubber. I enclose a drawing, but I think that the structure isn't "continuous" according to what you said.
At least not in the sense that it is in the inner wall and ceiling (which is covered by 2 layers of 5/8 gypsum). I'll borrow a digital camera and send some pictures, because what you're saying is very helpful and I don't want to do less or more than I have to. Thanks again.
Phil

knightfly · Post by **knightfly** » Tue Sep 07, 2004 10:18 am

Here's the concept you should be going for, just a quick sketch -

Basically, your outer wall mass should be sealed to an equivalent outer ceiling mass (not the weather roof, this needs to be vented) I'm talking about having two separate masses, with a roof over the outer one for protection from weather but NOT sound proofed.

Then, your inner wall mass needs to be decoupled from the outer one, but have a ceiling counterpart that is sealed to the inner wall, effectively making two envelopes of mass as shown in the sketch.

For extreme low frequency or best iso (like when you're upstairs from crotchety old ladies) the upper example is necessary.

When you're looking at your construction, compare the effect of what you have to this example, and it may help you see what else you need to do... Steve

Aaberg · Post by **Aaberg** » Wed Sep 08, 2004 12:17 am

Ahhh....give a man a fish, and he'll not go hungry that night. Teach a man to fish, and he'll quit all this studio-buildin' shit and get out on the river!
Yeah...makes a lot of sense. Low frequency iso is pretty good in the building, so I think I'll use your idea of sprayed foam, 6 inch studs, several layers of sound board with no space, lots of 703 jammed in there.
One thought I had while roaming the isles of Home Depot. There is a concrete siding called Hardi-board, etc. It has a very high mass per square foot. I can't find any info on STC for that, but it seems to me that if I sheath the walls with that stuff, it would improve isolation. Any experience or thoughts on that?
Thanks a million.
Phil

knightfly · Post by **knightfly** » Wed Sep 08, 2004 5:30 am

OK, first off you're putting words in my mouth - I did not, and will never, advocate sprayed FOAM for this purpose - I said sprayed CELLULOSE, which is a totally different product. Spray foam dries to a closed cell state, which is useless for anything but HEAT insulation or air infiltration. Just want to make that clear, in case you actually MEANT foam...

It may be a slang term, but don't actually JAM insulation - that would be too tight a pack, and would reduce isolation by coupling inner and outer leaf.

Hardiboard, Wonderboard, basically fiberglass reinforced cement board - heavier than hell, and I agree should be good stuff. Hard to fasten correctly, needs special screws, some places only carry wierd 3' x 5' pieces (used in bathrooms under tile, guess that's why the wierd size to fit tub enclosures) but supposedly DOES come in full sheets (I wouldn't wanna LIFT one)

I've not tried the stuff, but mass is mass - if you could get it up without breaking or cracking, and get past the difficulty of easy accurate trimming, etc, it would give more iso per thickness than sheet rock. I don't have actual specs on it, the few times I've used it in bathrooms it seemed like maybe at least 1-1/2 times as heavy as sheet rock.

If you could get the stuff up as an outer layer intact, and seal it well, I'd expect maybe 3-4 dB better performance per sheet than sheet rock, and maybe 5-6 dB better than OSB... Steve

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