Acoustic Treatment Phase 2 - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 51 Old 09-17-14, 10:24 AM Thread Starter
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My panels arrived last week and I installed them over the weekend. Installation was pretty easy. I used two screws with Sheetrock anchors per panel. The only real time consuming part is measuring for screw/hook locations on the wall and keeping them lined up and level. Each panel hangs with a wire across the back like a large picture frame (which also allows for easy height tweaking). As you can see I have three panels on each side wall positioned to catch first reflections from the left, right, and center channels for all seating positions. I kept my 2" thick DIY panels and have them stacked in the back corners to see if they'll help a bit with bass trapping as well. I have not had a chance yet to do any listening or measurements but I plan to do that pretty soon and post results here. Stay tuned! In the meantime, enjoy some poorly lit phone camera pictures!




Acoustic Treatment Phase 2-image-2594718269.jpg



Acoustic Treatment Phase 2-image-4195889246.jpg


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post #12 of 51 Old 09-26-14, 03:27 PM Thread Starter
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Re: Acoustic Treatment Phase 2

Ok, I've hung my new panels, moved some things around and taken some new REW measurements. With reference to my original post, I'm still focusing on my first target (30-60Hz range), even though it's not the only issue.

First - what I've changed. As stated above, I mounted 6 GIK 244 bass traps and moved my existing 2" panels to the back corners (stacked 3 deep for 6" thickness in each corner). I currently also have the privilege of borrowing a pair of Chane SBE-118 subs for an upcoming review, so I decided to see if dual subs could help with some of my problems. Turns out it helped more than anything I've tried so far, but I'm not convinced I'm anywhere near done with acoustic treatments. After trying a bunch of different configurations and EQ settings, I settled on placing the subs in the back corners of my room, and adding a boost at 18Hz on the Dayton amp. Below is a comparison of the single sub responses (various locations in the room) to the dual sub response I'm getting now.

Measurement Graphs

Single sub, 2" panels (x6)


Dual sub/rear corners, GIK 244 (x6) plus 2" panels (x6)




The good news: response from 20Hz up to almost 70Hz is about +/-3dB (compared to +/-10db worst case before). It sounds much better at the MLP too, of course.

The not great but not surprising news: this confirms my suspicion that dual subs are basically a necessity for me.

The bad news: issue #2 (100-200Hz) response looks awful, if not worse than before. Moving the mic around the seating area didn't make any major improvements in this area. I had anticipated the 244 panels to improve response in the 100-300Hz range a bit more than I'm seeing. How much do panel quantity, panel placement, speaker placement, and seating placement effect response in this region? I guess what I'm getting at is, do I need to add more panels/bass traps or is the room arrangement at play? Just to clarify, I have not bothered trying to EQ the big dip. I have tried 2 or 3 different speakers with similar results here too, which makes me think it's almost completely a room issue. I know room correction and EQ is always an option, but I personally want to get the room as good as I can without the use of EQ.


edit: I should add that I have tried different sub crossover and phase settings as well, and nothing made much of an improvement without messing up response above or below. I also added a waterfall graph for the current setup.


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post #13 of 51 Old 09-26-14, 03:36 PM
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Re: Acoustic Treatment Phase 2

Looks to me like the bottom end of your current trough might be a phase issue between mains and sub(s). Try reversing the phase on 1 then on both of them and see if you can at least get a part of it better. Above that it's likely boundary related phase issues (SBIR).

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post #14 of 51 Old 09-30-14, 02:56 PM Thread Starter
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Re: Acoustic Treatment Phase 2

Bryan - thanks for your quick response last week. I had some time last night to move things around a bit and take more measurements.

First, I tried reversing polarity on just one and then both subs. It did nothing to help the trough from crossover up to about 200Hz, and made things below 50Hz much worse. I played some more with the crossover settings and PEQ but couldn't get even marginal improvement in that area.

Since you mentioned SBIR, I took a quick look at GIK's page on the subject. I tried moving my loose 2" panels behind and beside the main, in the front corner, and on the side wall at the front of the room. It didn't seem to help much, but I wasn't being very scientific about it. Throughout the process I have tried two different types of speakers for the mains and a few different mic positions within the seating area.

After a while of that, I took measurements of the subs alone and the speaker alone. The sub-only curve looked very good up to 120Hz or so. The main-only curve still had the awful dip. I tried moving the main side-to-side a couple feet, and even about 2-3 feet into the room (very unpractical placement) and it did change, but I wouldn't call it better. See the graph below for before and after. The pink trace is the normal spot, pretty close to the front wall, on either side of my TV. The blue trace is probably about 30-36" out from the front wall, and probably about 2-3 feet from the mic.



I'm coming to the conclusion that my room dimensions combined with speaker placement are causing some major issues. Is it too much to correct with more bass trapping? I don't have much freedom with placement of the main speakers. Sub location is pretty flexible, but they seem happy in the back corners.


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post #15 of 51 Old 09-30-14, 03:34 PM
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Re: Acoustic Treatment Phase 2

If the sub is OK and the mains are bad, then either positioning or you need to work with thicker panels on the front wall or side walls pending where it's coming from. It's possible that you had problems in that general range for both front and side that were somewhat cancelling. When you fixed one, the other was no longer cancelled. It happens sometimes. Need to try something much thicker than 2" to try to fix that on the front wall.

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post #16 of 51 Old 10-09-14, 01:52 PM Thread Starter
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Re: Acoustic Treatment Phase 2

Even with the improved response of the subs being placed in the back corners, I wasn't satisfied, so I did some more rearranging. Turns out placing on sub at the center of the front wall and the back wall improved response even more. Still not perfect, but much better. Two PEQ filters and I'm a pretty happy camper considering what I started with. Too bad these subs aren't mine

Anyway, here is the resulting response up to 200Hz. Target response was around 75db with 20Hz being about +6db compared to 100Hz. Again, you can see the 100-200Hz range still needs some improvement.
edit: just want to point out my target curve was based on FR graph and listening/tweaking.


For comparison:
Blue - subs in rear corners
Purple - subs centered F&R
Green subs centered F&R with EQ


Relocating the subs seems to have compensated for the mains dropping off so steeply around the crossover point (80Hz in this case). I also found that putting 4"-6" thickness of damping material directly behind the mains and on the side walls directly adjacent to the mains seemed to even things out a bit above the crossover point, but that area still needs some work. Another huge benefit of this placement is that the bass is very consistent between the front and back rows now. Previously there was a huge variation.

I think the next step is indeed to get some substantial damping on the front wall, and possibly still do some corner traps. Making progress though.


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post #17 of 51 Old 10-09-14, 02:09 PM
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Re: Acoustic Treatment Phase 2

Looking good. 5db range from 20 to over 100 is great.

BTW, that's one of the suggested positioning strategies identified in the Harman white paper. The other is the center of the 2 side walls.

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post #18 of 51 Old 10-09-14, 02:32 PM Thread Starter
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Re: Acoustic Treatment Phase 2

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bpape wrote: View Post
Looking good. 5db range from 20 to over 100 is great.

BTW, that's one of the suggested positioning strategies identified in the Harman white paper. The other is the center of the 2 side walls.
Yep, that's where I had originally heard of it. Initially I hadn't planned to try it for a few reasons. First, I had tried the centers of the side walls and it didn't work any better than the rear corner placement. Second, the dual Chane subs are powered by a single Dayton SA1000 which makes for a long exposed wire run. Last, I had to slide the rear seat up a few inches to fit one behind it. Having tried most everything else I figured I'd at least give it a shot. I'm glad I did. Supposedly one sub centered on each of the four walls is a good option too.


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post #19 of 51 Old 10-09-14, 02:55 PM
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Re: Acoustic Treatment Phase 2

As is 1 in each of the 4 corners - but you found the one that works best for you which is good.

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post #20 of 51 Old 10-22-14, 11:26 AM Thread Starter
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Re: Acoustic Treatment Phase 2

Ok, moving on to the next step with the assumption that I'll settle on a dual sub setup for good response below 100Hz and maybe add corner traps in the back later. Now looking at the response of the mains from 80Hz to 400Hz. It appears I need treatment on the front wall now since moving the mains side-to-side or out into the room isn't practical and didn't provide a measurable improvement. So I'm looking at GIK 242 panels compared to 244 panels, for the front. The test graphs look to be given with different units, so I'm not sure what the difference is between the two in the range I'm concerned about. Do I...

1. move some or all of my existing 244 panels to the front wall and get some 242 panels for the side walls? (easy on budget)

2. leave 244 panels on side walls and add 242 panels to the front wall? (easy on budget)

3. leave 244 panels on side walls and add 244 panels to the front wall? (stretching budget)

4. something totally different?

Couple details - I can't do corner traps in the front vertical corners, and I don't want to go too thick with treatments on the front walls since I currently have a curtain hung for aesthetics. 244 panel thickness might be pushing it there.


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