Absorption coefficients of this trap?

I am trying to find out the absorption coefficient of the traps similar to these. http://www.johnlsayers.com/phpBB2/viewtopic.php?t=4581 I made some using the same design, and I would love to know how well these will absorb the the bass frequencies. I am also curious as to how these traps absorb compared to Ethan Winer's deep bass trap design. I have the specs on the roxull mineral wool I am using, but I don't know how much having a 2inch gap between the wool, and the wall will change that. The traps are built on a 1 by 4 frame with 2 inches of mineral wool, and a 2 inch gap. I need absorption to at least 100 hz. here is a pic of mine thanks

No one's going to be able to tell you for sure unless there's lab-measured data available for something very similar to what you've built. Even then, it might only be meaningful if the "before" and "after" airspace numbers are available to compare (assuming numbers on the exact absorber you've built are not readily available). In general, it would appear that a 1.5x to 2x increase in absorption in the 125 and 250 Hz bands when you add an airspace of equal depth to the thickness of the panel is not uncommon. Some data I've found on 1" mineral wool panels jives with this. I wouldn't expect drastically different results with a 2" material. This is very rough, but should help. Good luck!

It's diminishing returns...yes you get better performance by spacing the insulation from the wall, but you get even better performance from stuffing the full space with insulation. For example,:

1" thick 703 spaced at 0" has an absorbtion coef of .18 at 250 Hz 1 inch thick 703 spaced at 1" has an absorbtion coefficient of 0.25 at 250 hz 2 inch thick 703 spaced at 0" has an absorbtion coefficient of 0.8 at 250 Hz

If you can afford the extra insulation, the absorbtion coefficients are way better for a full stuffing, considering that they take up the same amount of room volume. 4" of insulation will give good absorbtion to about 100Hz but falls off sharply after that. At 100Hz or so, you should be looking at bass traps, like resonators/panel traps. Cheers Kris