I've found a supplier in my area that can get pretty much any type of insulation. They normally stock products form Ottawa Fibre and FibreX (I'm in Canada). The guy I spoke with say that they have lots of FibreX 1240 mineral wool and it sells for $4 for a 2" board. It's only 3lbs/ft² however. They can also get OC 703 or 705 but at a premium that is out of my budget. Ottawa Fibre has an equivalent.
I looked the coefficients on BobGold's site (http://www.bobgolds.com/AbsorptionCoefficients.htm) and the 1240 looks pretty much on par with everything else. I've read quite a few posts that recommend the 6lbs/ft² stuff (would be FibreX 1260). Is there really much benefit in going with the higher density? Is there any data (ie: REW measurements, etc) to support it?
I plan on making two corner chunks and covering the front wall as well as the first reflection points. Should I go with the 3lb mineral wool or is 6lb a must? Or should I save and go with fibreglass which is twice the price?
Thanks Bryan. The chunks will be 12x12x17 but I was thinking about doing the rest of the front wall with 2" panels. For the sake of a little cost increase should I just go with the 6.0lb stuff all around? The material cost is really not that much more in the grand scheme of things. If it's not going to make a lick of difference though the 3.0lb would be smarter. Any opinions?
Thanks for the fast reply. I'll post my build when I get a chance.
For the chunks do you recommend using poly batting between the rockwool and the outer fabric to stop any fibres getting through? I haven't sourced the fabric yet. Most likely it will be burlap or other breathable cloth. I'll have to browse my local Fabricland or Walmart to see what kind of deal I can get on black fabric. I'd like to do it right in the first attempt because time is the critical component.
You can do batting in front if you want. Won't hurt anything certainly. For broadband absorbers like these, the cloth selection is not as critical. If you can blow through it without busting a kidney, it will be fine. Muslin is usually a good choice and resonably priced.