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

They are probably very similar. The Owens 703 -might- absorb slightly more sound because it is a little bit more dense (Owens 703 is 3lb, Roxul Safe-n-Sound is 2.5lb), but that is such a small difference.

https://www.atsacoustics.com/page--Selecting-the-Right-Acoustic-Material--ac.html

This page will help you decide between different types of acoustic materials.  Be very conservative when putting in acoustic panels.  Placement is very critical and one panel could suck too much liveliness out of the room.  Placement is critical.  Experiment with different placements.

I just recently experimented with diffusion panels on the side walls. They did not work out at all. I was using the 23" x 23" QRD diffusors (the ones from ATS Acoustics). It took some critical listening, but what happens with the diffusors on the side walls is that they will emphasize/boost some frequencies and then subdue/cancel other frequencies. I believe when the sound waves are bouncing around in the slots, it creates enough of a delay that it will cancel out the waveforms of some of the frequencies by the time it reaches your ears. Turning the diffusor upside-down so that the deeper slots or closer or farther from you will totally affect the sound as well. I could not get the diffusors to work on the side walls properly whatever I tried. Since I had to put them somewhere, I put them on the back wall. They seemed to work okay horizontally, because vertically they still cancelled out some frequencies. I would be very careful with using the diffusors. Always test out locations first and listen CAREFULLY before permanently mounting them.

Absorption is good -- up to a point. I have found that just adding a couple too many panels could throw the balance of the room off so that it is absorbing too much sound. What happens is that it starts to suck out too much upper mids/highs and you lose the excitement of the room. It’s a fine line, but once you’ve crossed it, the room becomes dull.

I found the best placement in my room is to have a 24" x 48" x 2" panel behind each speaker (they are in the front corners). Then a 24" x 48" x 2" panel in each of the back corners of the room. Since the speakers are corner loaded, it prevents standing waves which really make the midrange blare/resonate. I found that doubling up the panels in the back of the room (by stacking them on top of each other making a 96" high panel or by doubling up the thickness so that it makes a 24" x 48" x 4" panel) will push it over the threshold where it’s sucking too much sound out of the room. I have a fully carpeted floor, so that is absorbing a lot as well. These are cheap foam panels. I have some Roxul Rockboard 80 on the way, which behave very similar to the foam but with much better bass frequency absorption.

I don’t know which model you have, but the ESL speakers look big, and they might be reflecting sound waves as well as generating them (I don’t know). I’m not sure about putting absorbing panels behind them, unless you put them up towards the ceiling.  Putting absorbing panels behind you sounds like a good idea (since you are so close to the rear wall). Maybe also look at points on the back wall where the speakers are directly aimed at and put absorbing panels there? Or maybe diffusion. Different things to try, lol.

At $47 for a 12-pack, you can just stack them up in the back of the room to see how it will affect the sound. They 15-1/4" are cut to fit between house frames. If you don’t mind putting up 3 panels instead of 1 or 2, it can be a cheap way to go. The Roxul are only 2.5 lb density, but they might be stiff enough to lay up against the walls. If you do this, be very careful. It is mineral wool fiberglass and always use a filter mouth mask and gloves when handling them.  There's a point where there will be too much absorption in the room.  You'll just have to experiment until you find that threshold.

The panels from ATS Acoustics are mounted in a light wood frame and wrapped with fabric. At $55-76 per panel, it’s really cheap for the build labor. Unless you are fine building them yourself.

One thing to know about the acoustic materials is that you need massive amounts of thickness if you want to absorb a lot of the lower bass frequencies. Yes, putting a space behind the fiberglass will help because the sound will bounce off the wall and back into the fiberglass. However, if you want to absorb the lower frequencies, you’ll need a very thick trap (like the 6-7" bass traps from GIK). If you want to put multiple layers of the fiberglass in, you need to keep them at the lower densities (like 2.5 - 3 lbs).

I chose the 2" thick 8 lb Roxul because I wanted to limit how much mid/high frequencies it would absorb, but I still wanted decent bass absorption. At a certain point, the denser material will start reflecting sound at a thickness level. A 4" stack of the 8lb Roxul will probably not work any better than a 2" stack. However, putting a 4-8" stack of 2.5lb Safe-n-sound will absorb a lot more bass (as well as a lot more mids/highs).

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.

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.