How Thick Should The Mineral Wool Be?

Hope this wasn't posted prior (I'm at work and don't have too much time to do a real thorough search) but using room in room construction, how thick should each wall's mineral wool insulation be? Current prices I got are: 3" = $1.05 (per sqr. foot) 2" = $0.78 (per sqr. foot) 1" = $0.25 (per sqr. foot) AND - do I NEED to use mineral wool or is there something else I can use? THANKS - THANKS - AND MORE THANKS!

Mineral wool isn't used for soundproofing, that's used for acoustical control within the room. For soundproofing you need mass. As for bass traps, if you want to fill the entire corner with mineral wool that's fine. It'll cost more, but that's entirely up to you.

with those prices, go with the 1", and just buy more of it. They don't need to be attached together, ie, you could put 4 pieces of 1" wool back to back, creating a 4" slab, for less price than the 3" slab. Of course it means more cutting and labor for you, which is part of the equation....

From my reading on here it's stated that there's very little difference between mineral wool and the pink stuff. Seems like the lower frequencies are comperable between mineral wool and the pink stuff but the lower highs to mids may be absorbed slightly better with mineral wool. I believe (as Sonic said above) mineral wool is suggested possibly for traps and acoustical treatment. Hey, if you're into the technical end, in the last link below, Aaron tracked down some good info the NRC reported concerning insulation in different type walls. Check these posts out... http://www.johnlsayers.com/phpBB2/viewtopic.php?t=5965 http://www.johnlsayers.com/phpBB2/viewt ... c&start=30 http://www.johnlsayers.com/phpBB2/viewtopic.php?t=2127 Hope that helps...

I thought - and always seen pictures of - mineral wool in the walls. Between the studs and the sheetrock. I always see people making their own acoustical panels (that you hang on the wall in a control room) out of Owens Corning 703 rigid panels. --- That being said ---- IS the PINK-STUFF really good? Will it work? Does anybody have it in their studio - and what are your findings?

Brad From my perspective I see no problem using Mineral Wool in walls if that's what anyone chooses. Yes, I've seen a lot of people use Mineral Wool in walls, ceilings, traps etc. I think the thought stated in the linked posts are that because there's very little difference in the performance of Mineral Wool compared to Pink insulation, it's more "cost effective" using the Pink insulation. Mineral Wool will give you slightly better performance at some frequencies over Pink insulation, but it's overall performance isn't too much better. Here's a quote from Steve (Knightfly) in the first link I listed in my last post...

You don't need rockwool for inside ceilings or walls; use standard fiberglass insulation and do a complete fill with slight (about 20%) compression - it'll cost closer to the same amount and do just as well. Save your rockwool for aocustic treatments.

Here's another quote from Steve from the 2nd link in my post above...

Within walls, there doesn't seem to be more than a dB or two difference between rockwool, mineral wool, rigid fiberglass or the "fluffy stuff", with a few cautions - this assumes that the cavities are mostly full, or (in the case of the softer, "fluffy stuff" insulation) slightly overfilled - letting the insulation touch the wallboard surface tends to help damp the panels, which improves wall performance.

It's just a matter of choice... :)

Current prices I got are: 3" = $1.05 (per sqr. foot) 2" = $0.78 (per sqr. foot) 1" = $0.25 (per sqr. foot)

This is what I got Roxul for here in MA: 3x15x64.95 - $25.60 /64.95sqr ft = .39 psf 3x24x64 - $21.76 /64sqr ft = .34 psf While the O.C. R13 3.5x15x32ft was $10.80 /40sqr ft = .27 psf So I used RockWool for mostly every thing.

I thought - and always seen pictures of - mineral wool in the walls. Between the studs and the sheetrock. I always see people making their own acoustical panels (that you hang on the wall in a control room) out of Owens Corning 703 rigid panels. --- That being said ---- IS the PINK-STUFF really good? Will it work? Does anybody have it in their studio - and what are your findings?

ltata wrote:

This is what I got Roxul for here in MA: 3x15x64.95 - $25.60 /64.95sqr ft = .39 psf 3x24x64 - $21.76 /64sqr ft = .34 psf While the O.C. R13 3.5x15x32ft was $10.80 /40sqr ft = .27 psf So I used RockWool for mostly every thing.

I'm in PA, so who was your Rock Wool dealer? Contact Info. Thanks!

Good deal Itata! Based on Steve's comments there's not much difference between all of the mentioned insulation. So, in your area if the Roxul is cheaper I'd go with that myself! :D In other areas some other type of insulation my be cheaper. BTW, did you price the regular "house" Pink insulation? Was it cheaper than then OC 703 or the Roxul?

I'm in PA, so who was your Rock Wool dealer? Contact Info. Thanks!

Your Welcome! http://www.karpp.com/ I got the contact info from thr roxul website - http://www.roxul.com/sw34066.asp

Brad, in addition to the above you should be careful NOT, repeat NOT, to use HIGH density insulation inside your walls; this will actually LESSEN the sound isolation at lower frequencies. Optimum for music isolation inside a wall is from about 1 PSF to 3 PSF, higher than that and you'll start to pass more low frequencies... Steve

But looking at the absorbtion (nrc) tables of the different wol types and brands there are differences. So does is pay to get a slightly more expensive wol with better absorption specs than a cheaper type with a lower NRC ? I mean, will it make that big a difference that one should be adviced to spend precious money on those higher NRC wol types?

Before that can be answered we need to specify WHERE the insulation will be used; inside a wall employing mass-air-mass construction, ANY insulation that's LESS than 3 PCF density and can pass AIR thru it will work essentially the same as any other; so the least expensive NON-foam insulation you can find is the best deal. For ACOUSTIC treatments INSIDE THE ROOM, 3 PCF fiberglass, mineral, or slag wool are normally the best; if you want less high frequency absorption (already have enough in the room) then the higher density wools from 5 to maybe 8 PCF may work for you; this is where you should "ballpark" your absorption needs by octave, and PLAN your acoustic treatments; at least a rough idea, which may/will need to be adjusted to taste. Two different uses, two different answers; HTH... Steve

Okay, but doesn't absorbtion inside the wall (behind the gypsumboards that is) make any difference ? So having cheap wol (about 3pcf / 40kg/m3 for us european folks) is the thing to go for anyway? I understand, for acoustical purpose (room acoustics etc) like panels this IS essential. Depending on what FRQ range you want to dempen you choose the right wol.

Absorption within the wall does make some difference, but it's different. I think part of why heavier insulation inside a wall WORSENS the low frequency isolation may be partly due to some "third leaf" effects of the higher density stuff acting more like another leaf of mass, but that's just conjecture on my part. What is NOT just conjecture, is this mammoth project by our Canadian neighbors - http://irc.nrc-cnrc.gc.ca/irc/fulltext/ir761/ir761.pdf If you check each similar wall construct there (about 350 of them) you'll see that ACTUAL TL at low frequencies is affected by the type and density of insulation, and that very little beats plain old lightweight fiberglass insulation - but, if you just want to spend more money, I'll not stop you :wink: Steve

Okay, good to know one can save some extra buckaroons on that issue. I was on the assumption that higher NRC was worth spending money on (in case of stacking it behind walls). If the difference in using cheap fluffy stuff isn't all that, I will reconsider since the insulation (together with the gypsheets) is the biggest number on my cost calculations (about 1500 euro's worth of insulation right now) Thanx for the link and, as always, the big help in general. ro

So should I have not used 3" Roxul in the walls? At this point in time I just have the inner walls up and I partly finnished the inside of the control room so I can still record while I build. Should I remove it? Can't from the wall next to the Foundation... :( Or should I keep it and when I put up the Outer walls use the pink fluffy stuff?

If the Roxul you used inside your walls is less than 3 PCF density (not thickness) it's fine. Tests have shown very little difference in any breathable insulations between about 1 to 3 PCF, and any trends tend to show slightly better LF TL with LOWER density - but I would NOT tear out a wall for such a slight change, EVER. Unless you can find a REAL bargain in Roxul or other higher density (more than 1 PCF but less than 3) I would just use the pink stuff inside any future walls... Steve

Thanks Steve! :mrgreen:

FYI most 3" AFB (rockwool that isnt semi Rigid) has a PCF of about 2.5. It's great in walls.

Ok kewl! That's what I used 3x15x64 AFB :D The price was real close to the pink stuff, only like .12 more per SF so I went with that.

You got it made; 2.5 PSF is considered optimum for in-wall insulation, but like I said there's little difference from below 1 up to 3 PCF. The fact that you got a deal just sweetens the pot... 8)