Sorry, that "2x thickness" wasn't right - 3" S&S seems to perform between 2" and 3" OC 703, and closer to 3" if anything:
Product density 125hz 250hz 500hz 1000hz 2000hz 4000hz NRC
RXL 80 1.5" 8.0 pcf 0.21 0.64 0.92 1.00 0.95 1.01 0.90
Safe‘n’Sound 3" 2.5 pcf 0.52 0.96 1.18 1.07 1.05 1.05 1.05
703, plain 1" 3.0 pcf 0.11 0.28 0.68 0.90 0.93 0.96 0.70
705, plain 1" 6.0 pcf 0.02 0.27 0.63 0.85 0.93 0.95 0.65
703, plain 2" 3.0 pcf 0.17 0.86 1.14 1.07 1.02 0.98 1.00
703, plain 3" 3.0 pcf 0.53 1.19 1.21 1.08 1.01 1.04 1.10
I am actually using Comfortboard IS rather than RXL 80, but apparently the two have very similar behaviour.
One thing I don't understand is that the absorption coefficients don't go up that much at high frequencies as thickness increases, but I was also under the impression that adding layers would more or less result in adding the absorption coefficients. I guess the latter belief must be wrong ?
