wall insulation

sourrox · Post by **sourrox** » Fri Jul 09, 2004 7:29 am

I'm having a hell of a time finding 703 or rockwool. Ive called many many places here in LA and have had no luck. A guy at Viking insulation in Burbank said he has Johns manville 300 series semi ridid fiberglass which he says is the same as 703. is this true? its 2" thick and 3lb pcf. sound usable? how much isolation loss is there really if plain old r-13 or r-19 is used in my walls. is there really a noticable difference. Ive read a ton on this site but never really found a clear answer on this.
Thanks, DD

Post by **Aaronw** » Fri Jul 09, 2004 8:04 am

I believe it is similar to 703.

Click here and contact Roxul for a dealer near you...

http://www.roxul.com/sw34462.asp

You want the AFB product... http://www.roxul.com/sw34142.asp

sourrox · Post by **sourrox** » Fri Jul 09, 2004 8:31 am

I just got off the phone with a gentleman from Insulation Wholesalers in Pamona. great news! they carry Roxul products and its very inexpensive.
3" thick 2.5 pcf for $21.50 a bag (8 2'x4' pieces) does this sound like its what I need? he also has Roxul safe which is 4" thick and 4.5 pcf for about the same price. would this be better or is that too dense? I'll be ordering it as soon as I decide which of these will be best for inside my walls. If all goes well, I'll put his contact number on the "where to buy materials" board. thanks, DD

z60611 · Post by **z60611** » Fri Jul 09, 2004 8:45 am

You can compare various products (including 703 and roxul's stuff) as well as see other manufacturer's at
http://www.bobgolds.com/AbsorptionCoefficients.htm

What I do is get a hold of a local insulation contractor, as you've already done, and then look up what they have in stock on this web page to see if it'll do what I want.

Where is the 'where to buy materials' board? This sounds nifty!

AVare · Post by **AVare** » Fri Jul 09, 2004 9:07 am

Where is the 'where to buy materials' board? This sounds nifty!

It is a good idea in theory, but quite often people don't even know how to use their phones. On another forum we are both on someone posted a couple of days ago if his local Home Depot carried a certain product.

I didn't have the heart to look up the HD's phone number off of any of the numerous web yellow pages, post it, and tell him to call that local number to find out.

knightfly · Post by **knightfly** » Fri Jul 09, 2004 8:22 pm

DD, I don't have actual dB numbers on insulation comparison, only a study by USG which found that for music the ideal weight for insulation blankets inside walls is 2.5 PCF - lighter than that improves bass TL slightly, heavier than that improves midrange. A gain in one range = a loss in the other.

If the 2 to 3 PCF stuff can't be found, several people have reported good results just using standard fluffy batts in walls - given the option, however, I'd stick with tested results and use the heavier (2-3 PCF) stuff... Steve

z60611 · Post by **z60611** » Sat Jul 10, 2004 4:08 am

Knightfly:

Does that mean you'd recommend in a double stud wall that one stud be filled with 2.5pcf rockwool, and the other stud be filled with R19 so that it also filled the airgap with fluffy without coupling too badly. Or am I just being silly.

sourrox · Post by **sourrox** » Sat Jul 10, 2004 5:26 am

I hope your on to something there cause that is what I will have as well. the outer garage wall studs already have fresh r-19 in them and I'll be putting the Roxul 2.5 in the inner wall studs. I'll be sure to post my results when I'm finished. Knightfly, thanks for clearing this issue up a little for me. I'll post some pictures over the weekend of my construction so far. thanks again, DD

z60611 · Post by **z60611** » Sat Jul 10, 2004 11:05 am

sourrox

The reason I asked if I was being silly was two fold
a) the primary reason for insulation is to increase the damping of the leafs. The most interesting damping that we want to hit is the resonance and other LF. Using two materials is something else to order, and targeting the wrong frequency seems bad. Nevertheless the only study I've ever seen is the USG one that Knightfly refers to, which is talking about 2.5pcf for STC frequencies. Which of course leaves me unsure as to which frequencies the insulation is good for anyway.
b) knightfly's bit about fluffy insulation being better for LF sounds like something I've heard, but I'd also heard that it's dependant upon thickness. There's a real limit to how thick I'm willing to make a double stud wall, so more dense within reason seems a better way given how thin I want to make the wall (8" between leafs). The actual quote I'm thinking of is this one by Terry M

If you build an absorber 12" thick instead of 1", it will absorb the same at 1/12th the frequency, but you have to change the material to one whose flow resistivity is proportionally smaller. So lets say you scale up a 1" thick absorber made from Fibertex 650 Rockwool, which has an acoustic resistivity of about 50000 mks Rayls/m. If you divide this by 12, you get about 6000 mks Rays/m. That's roughly the resistivity of fiberglass batt.

My guess, and I'm almost always wrong when I guess about acoustics/walls, is that 2.5pcf rockwool in both studs is a good thing, with the middle of the rockwool pressed or glued against the gypsum to increase damping.
However, the reason I mentioned the R19 is because I seem to recall someoen mentioning that there's a building code that requires no air gaps in walls, which means it has to be filled with something, so why not something less rigid like fluffy pink R19 fiberglass.
I don't know.

How about this for a hypothosis, if 2.5 pcf rockwool is good in a normal single stud wall (3.5" gap), and we up to a 8" gap double stud wall, then we need insulation with half (8" / 3.5") the rayls/m.

sourrox · Post by **sourrox** » Sat Jul 10, 2004 12:25 pm

interesting theory. you'll have to post if you ever try it out in the real world. I'm going with the r-19 and roxul combo because the r-19 is already in and the inner walls are already framed up. too late to change. I think it will work out nicely (crossed fingers) thanks to all for the replies. makes me feel like i'm not doing this project all alone. DD

z60611 · Post by **z60611** » Sat Jul 10, 2004 12:43 pm

You probably know this, but the rules for insulation installation are
a) make sure that every square foot (not cubic foot) is covered. The idea is to make sure that the sound has to go through insulation, and can't go around it. This is dimensions X and Y
b) beyond that, in the Z dimension, thicker is better (which you've got covered with R19 and roxul safe n sound?)

IRC 02-108

Adding a sound absorptive material inside the cavity of a single stud partition (wood with resilient furrings or steel) or a staggered wood stud partition increases the STC rating by 5 to 9 points depending on the type of sound absorptive material used. For double stud partitions, an increase of 10 to 13 points was obtained depending on the amount of glass fiber insulation added to the cavity.
Generally, at low frequencies, the increase in the transmission loss of a partition obtained by adding a sound absorptive material inside its cavity is equivalent regardless of the material used. Above 250 Hz, mineral fiber and blown cellulose give the best results; mineral fiber insulation provides slightly better transmission losses than glass fiber, especially around the critical frequency. Also, in the case of glass fiber, a greater transmission loss can be achieved by using denser batts.
With the exception of sprayed cellulose, the best transmission losses were obtained when the entire cavity of the partitions were filled with a sound absorptive material. When the entire cavity is filled, caution must be taken not to use a material that is too dense, otherwise a mechanical coupling could occur between the two sides of the partition which could result in a degradation of the sound isolating performance of the partition, as was observed in the case of a partition whose cavity was filled with sprayedon cellulose.

knightfly · Post by **knightfly** » Wed Jul 14, 2004 11:43 am

A comment on the last sentence of that last quote - sprayed cellulose is actually pretty rigid from what I've seen, so most likely contributed to too much coupling between wall leaves.

Rockwool is kind of similar, in that it doesn't have a lot of "give" - for that reason, I'd be careful about using rockwool all the way through a wall and using any compression to speak of - however, using fluffy stuff in conjunction with rockwool or rigid fiberglass should give really good results from all I've read (I've not tried this combination though) -

Just generally, within the range of normal insulation densities (.8 PCF to 6 PCF) the lighter stuff does better at low frequencies, at voice frequencies (and the center STC frequency of 500) the best balance (USG report) is around 2.5 PCF - going lighter than 2.5 improves bass TL at a cost to high frequencies, and going heavier improves high frequency TL at a cost of worse bass TL.

Since bass is harder to stop than mids or highs, for a music studio the lighter material makes as much sense as anything. Having a variation happening within the wall should get you best of both worlds. Just be careful NOT to use all rockwool and compress more than just a tiny bit, or you'll couple your two leaves too much and lose performance.

Just a thought, may or may not be true - since placing a third leaf in a wall tends to worsen bass performance and improve mid-range, and since using denser insulation also does the same, I'm thinking that if you use different densities in a wall the denser should be nearest the panels, with the lighter stuff in the middle; or at least, don't put dense stuff in the center and light stuff on both sides. This seems to me like it would be nearly equivalent to a third leaf in its effect, which is NOT what you want for music...

Remember, that last paragraph is mostly "mind-farts", so please don't go spreading it as gospel anywhere... Steve

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