Is there any real difference between Rock wool, Acoustic cotton and OC703? Is one more efficient then the other or more efficient at different frequencies? Where can I find info on this?
They are all about the same. Mounting and placement are far more important than the material.So, for a 2" or 4" thick 2'x4' absorber, which is the best material?
I have to respectfully disagree too. As Bob Golds says on his web site "Differences in coefficients of less than 0.15 are not significant." Not to mention the fact that absorption coefficients greater than 1.00 are possible only because the material’s edges are open to the noise in the test chamber, but not included in the surface area calculation. Therefore thick materials will always act differently in the real world than in the test chamber especially if they are mounted in such a way that their edges are not exposed to the room. If you cover an entire wall floor to ceiling and edge-to-edge, you have no exposed edges, and the numbers you have quoted will not apply. So I do believe that mounting and placement are more important. This is especially true when they are placed at a point to prevent a first reflection from your front speakers, which is an important factor in maintaining proper imaging of your sound field.I'd have to respectfully disagree. Each material can be made to work for a certain situation but they're not at all the same.
2" 3.5 lb mineral wool
0.26 0.68 1.14 1.13 1.06 1.07
0.17 0.86 1.14 1.07 1.02 0.98
2" 3lb Acoustical Cotton
0.35 0.94 1.32 1.22 1.06 1.03