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

I'm going to make some sound absorbing panels to place on the wall behind my listening chair. Owens Corning 703 and Roxul Safe 'n' Sound rigid boards are two choices to make them with. Anyone have experience with both, or even one?
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bdp24 OP
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Thanks Spencer. I had a session today, and the studio owner had real good acoustical treatment of his walls---a mixture of RPG diffusors and absorbers. I have a couple of spare 9" x 3' ASC tube traps---maybe I'll put them right behind the listening chair, with a couple of 2" x 2' x 4' panels stacked on top, for higher frequencies.
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bdp24 OP
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I was back near the same Home Depot today with a little time on my hands. I went in and looked for the Roxul Safe ’n’ Sound myself this time, and found it right on the shelf. S’n’S is 3" thick, and soft and loose, very limp, not at all like the OC703 semi-rigid panels, but more like cotton batting. Acoustimac offers empty 24" x 48" DIY panel frames in various depths, including 6". I’ve read that having a space behind the acoustical material will increase a panels ability to absorb low frequencies---a good thing for me due to the listening position being so close to the rear wall, but what if I was to stuff the frame with two layers of the 3" thick S’n’S? Possessing it’s 2.5lb. density, a 6" thickness of S’n’S won’t reflect back much of the mids and highs hitting it, but will that thickness absorb more, or less, lower frequencies than will a single 3" layer with a 3" space behind it? Acoustimac offers the frame both with and without a thin plywood rear back panel. Since my panels will be right against the wall, I surmise that back wouldn’t affect its performance.
auxinput
2,920 posts
 

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.

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sbank
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Excellent point about the thickness of 703 being so important at that frequency, but low frequencies are more likely to gather in the corners and the panels behind you on back wall will most likely only affect mids and highs so I would focus on absorption properties at those frequencies for you back wall panels. Corner traps behind you can use air gaps to absorb even deeper in the low frequencies. Corner traps in all 4 corners are the best way to deal with LF issues. The stuff behind your head can help with reflections, flutter echo, etc.in mids & highs. Cheers,
Spencer
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bdp24 OP
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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.

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