famous beagle said:
Are these rockwool boards the same size (2'x4')? Are there acoustic properties comparable to the 703? Are they more difficult to work with or something? I'm just tying to see why I would pay more than twice as much for the 703.
Thanks
The rockwool boards come in various size options just like the rigid fiberglass. I got 2'x4'x2" boards and 2'x4'x4" boards. I got both 6pcf and 8pcf densities.
They are very easy to work with, we cut some with a drywall knife and it cut like butter. We hung them with fender washers and 3" drywall screws. Some of them hit studs... others didn't. The 2" boards are not very heavy-- even the 8pcf boards.
I don't know why people would pay more for the fiberglass. I haven't done any type of comparisons between rigid fiberglass or rock wool so I have no authority to comment on their similarities/differences. I'm just trying to figure this stuff out like everyone else. From countless hours of reading/researching this stuff, I decided that the published numbers for rockwool and rigid fiberglass were identical enough that I could treat them as such and not worry about it. Whether that is a valid conclusion to draw is another matter.
The following OC numbers came from Table 1 on Ethan's site.
http://www.ethanwiner.com/acoustics.html
The rockwool numbers are from
http://www.fibrexinsulations.com/pdf/SoundAttenuationFire.pdf . Fibrex was the brand of rockwool boards I got from SPI. Notice the Fibrex .pdf doesn't mention density.
_______ 1 __ 2 __ 3 __ 4 __
125 Hz 0.17 0.60 0.27 0.97
250 Hz 0.86 0.50 0.55 1.28
500 Hz 1.14 0.63 1.07 1.25
1000Hz 1.07 0.82 1.10 1.10
2000Hz 1.02 0.45 1.10 1.10
4000Hz 0.98 0.34 1.10 1.09
NRC___ 1.00 0.60 0.95 1.20
1 = Owens-Corning 703
2 = Owens-Corning 705-FRK
3 = Fibrex Rock Wool 2"
4 = Fibrex Rockwool 4"
Spare me the stuff about the dubiousness of published NRC numbers and that stuff-- I don't care. I've put this stuff in two rooms and I've heard the difference it makes. I've got both fiberglass and rockwool and they both seem to work really well. I haven't lost any sleep pondering whether the rockwool is working as well as the fiberglass. Also, I'm fully confident that I have these panels placed in the most ineffective, inefficient, and inept manner possible... LOL! We didn't do any measurements... we just slapped them up all over the place. I knew I needed and wanted some room treatment and this was the cheapest (and apparently more/most effective) route to go. I've been very happy with the results.
Here's a pic of part of my buddy’s room. The room is "L" shaped and this is the little drum area. While I'm definitely a "function over form" kind of guy, I do try to add the "form" part into my work. But my buddy said he didn't care how it looked so we did it in the cheapest, fastest, and easiest possible way (notice the now-defunct garage door opener... LOL!). The room is actually much bigger (the majority of a 2-car garage), but the basic pattern of tiles is the same all over the room. Those are 4" panels in the back corners.
Hope that helps.