[klh]

The Knauf website has this as the absorption spectrum for plain 4" 3.0 PCF rigid fiberglass:

125 Hz   250 Hz    500 Hz   1000 Hz   2000 Hz   4000 Hz    NRC
  0.95     1.11        1.17       1.07    1.07        1.06       1.10

This looks pretty good. In fact, even when comparing 2" 3.0 PCF v. 2" 6.0 PCF, the 3.0 PCF has better numbers. Does this make sense? Up until about 6.0 PCF, I thought the higher the PCF, the better the low end absorption. Their numbers seem counterintutive.

[Ethan Winer]

K,

> Up until about 6.0 PCF, I thought the higher the PCF, the better the low end absorption. <

One problem is absorption is usually measured with the panels flat against a surface, but that's not how they're mounted for bass trapping. Another problem is the data rarely goes below 125 Hz, and there are important differences below that frequency. Yet another factor is the panel thickness. When using thicker panels you can get similar absorption with lighter material. You'll probably find my Density report interesting:

www.ethanwiner.com/density/density.html

--Ethan

[klh]

Once again... thank you Ethan