Confirming the usefulness of absorbtion panels

[jdarg]

So today I built a 3x5 ft. Frame out of two 8 foot 2x4s I had laying around. Stuffed it with two layers of ultratouch denim insulation I had left over from rebuilding my jbl 4560 bass horns. Put garden weed liner on the back surface and some parts express speaker grille cloth I had laying around for years on the front.

I tried landscape and portrait behind my listening chair and settled on portrait. So 3' wide by 5' tall behind my chair about 16" off the ground.

The improvement is pretty substantial. Everything just seems "blacker" and it seems to have pulled the soundstage closer to the front instead of being on or behind the front wall. I like it. Definitely much less echo in hand claps in my room.

I took a bunch of measurements along the way. Portrait, landscape, door open, door closed in my 10x10 room. I know what I hear, and I think certain measurements provide evidence, but what am I really looking for in my measurements to confirm the improvement in room eq wizard before vs after?

Group delay seems much cleaner. Ect as well. The clarity numbers were also better and the spectral improved by 100 or 200 as well.

I seem to need less attenuation in my room eq by 1 or 2 db esp. in the top end. I have a open door right to the left of my chair. Landscape seemed to really help the right channel but I have to offset it more to the right in that position. Landscape seemed to be a better balance of improvement between left and right channels so I stuck with that.

Any suggestions on what to look at to objectively measure the improvement in Rew?

I'll post my measurements but not in front of the computer right now.

 

[AllenB]

You could do a before and after and look at the impulse to see the reflections.

I seem to need less attenuation in my room eq by 1 or 2 db esp. in the top end.

This may serve to demonstrate why it is not instructive to use listening position measurements to EQ. You were changing the level when you needed to be changing the acoustics. The way you are doing it now is the more correct of the two.

 

[fluid]

Any suggestions on what to look at to objectively measure the improvement in Rew?

The best graph to show this would be the ETC (Energy Time Curve) which you get from the Filtered IR tab in REW.

 

[analog_sa]

The improvement is pretty substantial.

That is what counts.

In my room it is less clear. Yes, it sounds different. Perhaps in some rooms and for some tastes the introduction of random absorption brings unqualified improvement. In others it calls for the introduction of diffusion.

In REW you should look at RT60 and most importantly at the waterfall. It takes a while to find the best position for the most constant with frequency RT60.

Same as everything else in this hobby, the results of acoustic treatments can easily make things worse. Be careful and listen critically after every change.

We are after more enjoyable sound and not just numbers and graphs, right?

 

[JMFahey]

We are after more enjoyable sound and not just numbers and graphs, right?

true, that is the ultimate goal, but IF we have a different sound, it MUST measure different.

If you compare two systems, and one is more enjoyable than the other, then by definition they sound different.

If they sound different, they will measure different.

Then take a good hard look at measured differences, and try to correlate that to perceived listened difference.

 

[Joel Wesseling]

"Any suggestions on what to look at to objectively measure the improvement in Rew?"

For me the answer is simple - The measurements that are closer to Free Field Outdoor measurements. My old room was near anechoic and stereo playback was an absolute pleasure. Now that I have moved I'm planning to build a similar room, that will require a lot of absorption.

 

[AllenB]

I'd add that reflections within about 10ms of the direct are more of a problem. A rear wall close behind you can complicate this but after this time period you may want the reverberant energy.

 

[jdarg]

Thanks for the comments. I took some more measurements a couple days ago and will post those soon.

I'm not seeing a significantly better etc in the first 20 ms but it definitely falls faster overall with the rear panel. I think maybe I need to explore going after the side walls instead but I'll have to rotate the whole rig 90 degrees to get two parallel side walls with no doors or windows. One more data point if nothing else, I guess.

I was a little surprised that the first 20ms is cleaner if I sweep at 90db instead of my normal 75 or 80. I don't think that is a typical result, is it? I do have some rattles the lf part of the sweep sets off so I wonder if that's why? The louder the overall signal the more it swamps those rattles out? I think I can possibly see them as islands late in the lf parts of the waterfall too. Some sweeps rattle less than others. I'm going to go after those this weekend I think its just some items on the walls that I need to isolate a bit.

There's no avoiding the rear wall reflection in a 10' room when I'm sitting inches from the rear wall. This is why I figured I'd start there seemed like if it wasn't the worst offender it was certainly top 3 and I only have one panel right now. I'm not quite ready to start drilling into the ceiling either. I do have a rug covering about 80% of the floor but a pad under that might be a good idea too.

 

[63127]

The great advantage of Ultra Touch is the absorption coefficient is very uniform from 100hz past 7000hz, around 1.2 to .9. This is my secret weapon in transmission lines I build because only the first 25% of volume is filled greatly increasing the efficiency yet attenuating the modes.

Try to get a RTA of .333ms across the bands form 250hz to 4000hz. This seems to be a sweet spot for many studios and living rooms.