Owens Corning 703 vs. Roxul Safe 'n' Sound?

I had to google around and think about this question. There really wasn’t a good answer, but...

Putting an air gap behind the panel is not going to absorb more mids/highs that are already being absorbed -- unless you pull the entire panel away from the wall. This allows mids/highs that are coming around the panel to reflect off the wall and into the back side of the panel.

I have read that an air gap behind the panel will enable the panel absorb bass that is an octave lower, but remember that any bass waves going through the panel are going to resonate the wall as well. If you look at the difference between Owens 703 2" and 4".  You’ll see that the 4" thickness is 5 times as affective at 125 Hz (0.17 vs 0.84). Based on this, I’d stack two layers of 3" to make a total of 6" if I wanted to absorb more bass. The "air gap" is really just a tweak to boost bass absorption on thinner panels.

All good points, guys. My desire to get some absorption of lower frequencies at the listening position originates from having read that bass modes/nodes build up at not just room corners (though that is where they are most prominent), nor not just also along all the rooms wall/floor/ceiling intersections, but also along the wall itself---sealed rooms sound "bassiest" against their walls.

I know it takes a whole lotta material to absorb very low frequencies (below 100Hz), so perhaps going beyond the 2-3" of typical absorptive wall panels would bring marginal improvement in that regard. I have room to place a 9" ASC Tube Trap at either side of my chair, so I could do that and set the wall panels atop them. The rooms two front corners (behind the speakers) will have 11" Traps stacked on the big boys---the 16 inchers, the rooms back corners stacked 9" Traps.

Thanks again ya'll---Eric.

Yes, that is true.  There can be a benefit to putting bass traps in the middle of the walls.  However, you will only be able to attack some of the axial room nodes (not all).  It's still a benefit, though.  The link here does a room node calculation for my current HT room:

http://amroc.andymel.eu/?l=17.5&w=11.25&h=9&ft=true&r60=0.6

If you move your mouse pointer over each of the axial room nodes (the tallest lines on the frequency chart), you'll see in the "Room 3d" graphic that some nodes will build up on the front/back walls, some will build up on the side walls and some will build up on the ceiling/floor.

Interest article I found here:

http://ethanwiner.com/density.html

Where Ethan Winer found that putting Twelve 3" 703-FRK panels in a room absorbed more bass frequencies than Six 6" 703-FRK panels.  These are frequencies down in the 40-80Hfz area.  Makes me think of using the 703 FRK instead, because my room is becoming a little too dead with the Rockboard 80 panels even.