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Originally Posted by Nosound  According to one suppler that sells rook wool states that rock wool is only good for 100Hz and above is this true? |
No - neither rockwool nor fiberglass is intrinsically superior acoustically - they are generally equivalent but you must choose the grade of either material based on its physical properties.
OC 703 is a 3 lbs. semi-rigid fiberglass board that is a very efficient compromise of handiness [not too floppy, not to flakey], price, weight, and space efficiency [has sufficient gas flow resistance to work as a broadband absorber in corner mountings even with panels as thin as 4"].
To match these attributes in rockwool requires a higher density because of the nature of the material. Generally you could expect similar acoustic performance with a panel about 50% denser in grade [this would approximately match the gas flow properties of 703] which works out to about 5 lbs. per cubic foot or about 60 kg/m3. But even at this density rockwool has inferior handling properties to 703 and yields a heavier panel [no biggy for a hang forget application, but if portability matters this is a flaw].
Bottom line - if price in near equal I would go with 703 [lighter panel, easier to work with] - but if you can gain a significant price advantage use a +/- 60kg rockwool.
You can use lower density rockwool [less than 60kg/m3] or fiberglass [less than 3 lbs. per cubic foot like 703] but in both cases the stuff gets really floppy which means you need to build a more substantial frame, AND you need to increase the thickness of the panels.
Regular pink fluffy insulation will make a great broadband absorber - but you need upwards of upwards of 1.5' of thickness to work low in the band [get broadband performance].