John Sayers' Recording Studio Design Forum Archive

Steve,

In-wall use. USG did some studies eons ago about using higher density insulation to improve STL/STC. What they found was a marked difference between 0.7-1.0 lb/ft³ "batts" and 3-8 lb/ft³ "boards," like Mineral Fiber. The difference was only 1-2 STC points max (for "standard" wall construction) and the changes were mostly at 500-4000 Hz. Again, nothing to write home about, but for the more critical commercial and industrial situations, it could be the difference between being visited by OSHA and not.

FWIW, they found that there were diminishing returns above 8 lb/ft³. They asserted that 2.5-4 lb/ft³ was "optimum," all things considered. But they had also just developed a 2.5-4 lb/ft³ insulation that they wanted to sell the poop out of. Having worked with myriad studio designers over the years, we've found that they have a preference for 6-8 lb/ft³. Some swear by it.

YMMV...

Just spent a little "quality time" with IR-761, looking for correlations - the only wall constructions I found that had a counterpart with different density insulations were all one layer of 16mm gypsum both sides, using 90mm steel studs - these were 93-002 (used 75mm of 44kg mineral wool) and 93-003 and 338, which used 83mm of 98 kG mineral wool - all examples were essentially identical @ 50 hZ, running around 21-22 dB, but the lighter insulation came in 3-4 dB BETTER for STC, which seems to be exactly opposite of the USG insulation density report which (in a roundabout way) claimed that heavier insulation worsened LF TL, while lighter insulation IMPROVED the LF TL.

Also found this -

http://www.naima.org/pages/resources/li ... /BI405.PDF

which basically says same STC regardless of density, that only thickness matters, and that the first inch is 'way more important than the rest -

Starting to be even MORE convinced that for in-wall, anything but closed cell foam is fine, just throw it in there and obsess about something ELSE... Steve

Thanks for the research Steve.

Steve,

knightfly wrote:which seems to be exactly opposite of the USG insulation density report which (in a roundabout way) claimed that heavier insulation worsened LF TL, while lighter insulation IMPROVED the LF TL.

Are we talking about the same report? Mine is a technical report from Form & Function (FF-85-2B).

Starting to be even MORE convinced that for in-wall, anything but closed cell foam is fine, just throw it in there and obsess about something ELSE... Steve

And I would generally agree:
Empty is bad.
Solid (closed cell or hardening foam) is bad.
Low to medium density fuzz is good.

But again, I go back to the fact that some consultants and designers swear by the heavier (but not too heavy) stuff. And as long as those guys are demanding it...

One other thing I will say about higher density (6-8 lb/ft³) Mineral Fiber (or other fuzz): You can't beat it for seating risers. I realize this is OT, but it also applies to floated floors. We always suggest our Mineral Fiber to fill seating risers in home theaters. The reason we do this is risers or floors filled with lower density stuff "ring" more. We experienced the unfortunate drawback of lower density recently with a seating riser where we had no choice but to drill large holes in the riser and blow in cellulose insulation. While the difference between the cellulose (~1 lb/ft³) and empty was drastic, it just did not perform as well as the Mineral Fiber risers we've done. Still a little resonance in the 20-40 Hz range that might be annoying once the subs are fired up.

But then again, kids these days; they LOVE the bass...

I was referring to this page -

http://www.usg.com/Design_Solutions/2_3 ... onperf.asp

I have to agree on the risers/floors thing - this was forcibly etched into my brain (and ass) last year; Ann and I went to an Earth Wind and Fire concert in Portland; held in a converted theater/auditorium - they thought it would be cool if the drums were set up on this "tower" - so there was a riser about 4' tall on stage, fairly large, where another riser (about 4' tall) sat on top - the larger riser also held some dancer chicks, the upper one held the drums. If I could have chopped off the drummer's feet, the concert would have been very enjoyable - as it was, it was only bearable because we both had earplugs, and even then it sounded like "baby just got a new 10 KW sub" - and hadn't yet discovered there was a setting other than "12" -

As you also mentioned, the younger whelps in the audience (who probably thought they had "discovered" this "new" band, BTW) didn't seem to mind... Steve

Steve,

knightfly wrote:I was referring to this page -

http://www.usg.com/Design_Solutions/2_3 ... onperf.asp

Yep. That's the one. Thanks for the link. I also edited my post above to reflect their actual conclusion: 2.5-4 lb/ft³. (That'll teach me to skim...)

Jeff:

Do you have the graphics that go with the article? Several parts of the text refer to them, and they are not on the USG page.

Thanks
Andre

Sheesh!. My comments are for all the newbies that want to pop in here on this site, look around for a bit, and figure they are now experts. No way! I havent a clue about anything your talking about. Stay sitting down, dont get up to explain. All the little abreviations, technical words, makes me realize there is a lot to this if one wanted dive into it.

Dont bother to explain, If I spend enough time here, Ill pick some of it up. Its just a little humbling....... thats all.

d

D, sorry about that - you just got your thread temporarily hijacked; Andre is better versed in a lot of this stuff than I am, Jeff is the chief acoustic engineer for Auralex, and I've been studying this stuff off and on for over 20 years; I can see why it would seem a bit overpowering when we all stop explaining things and just start rapping on some level where we're temporarily not trying to explain basic concepts - not to worry, ask ANY question you have, someone will take a crack at it. That's the idea here, mostly. Sorry about the diversion... Steve

Nah, its totally fine. My question about the foam was answered fine. As you guys with more knowledge and lingo chat, I just realize that this studio thing can be really indepth...

d

d: My apologies also. I seem to take things off topic quite a bit...

Andre: I have only a print copy of the report. Since it's copyrighted material, I cannot post it here. E-mail me!

lovecow wrote:Foam, "Rockwool," whatever...

Seriously, just thought I'd let folks know that you can order Mineral Fiber (same stuff as "Rockwool") in 2" or 4" thick 2'x4' sheets from any Auralex dealer. Ours is 8 lb/ft³ density. Absorption coefficients are on our Master Table (PDF download). Price is probably not "almost free," but we try and keep it competitive.

Thanks for the info! I am quite overjoyed, as I have been in pursuit of OC 703, with no luck. The specs on this stuff are quite spectacular, and while it is not as cheap as similar OC products, it is cheaper than foam. What a terrific deal!