# Small Home Theater Acoustic Before/After



## Patzig (Oct 10, 2012)

I have a pretty small dedicated home theater room. 12.5 ft long, 10 ft wide and 9 ft ceiling. I posted a thread a while back getting some help on setting up acoustics, thanks to bpape and others. I ended up doing 2'x4'x2" oc 703 panels 2" off the walls/ceiling on most 1st reflection points. I also did 4" thick oc703 panels straddled in back corners, floor to ceiling and another one on front wall to ceiling corner for "bass trapping". I wanted to do the front wall to wall corners, but couldn't really fit them in at the time. So here's what I had for before with no treatments, then after with all panels mentioned above. All speakers, 5.1 and subwoofer. Another note: those peaks at 90hz and 120hz were actually fixed with subwoofer relocation, not acoustic treatments.




























Full disclosure: These measurements were done with a UMIK-1 mic. The before treatments were done with the original calibration file. Shortly after, "corrected calibration files" were released, and the 2nd measurements were done with that file. I guess I could have used the original file to see more accurately the changes the acoustic panels made, but oh well. So obviously the panels greatly helped with decay times at 200Hz and up. And they helped with FR somewhat.

So now I want to continue improvement and work on everything below 200Hz. I know my room is very small, which will make it difficult, but I think I can still improve it. Right now my seating is around 30% from back wall (want to move closer to 38% soon) which gives me 2-3 feet of unused space in the back of the room. So i wondered about building a whole wall bass trap back there. It would actually be fairly simple and cheap. My thoughts were to use OC R-30 Pink Fluff at 24" deep filling the entire back wall, wall to wall, floor to ceiling, with supports in between stacking as to not let it all get too compressed. Then build a simple false wall over it, maybe some 2x4 framing and black cloth or curtain to cover it. 

Questions: 
1. I know building this wall will definitely help with FR and decay times < 200Hz. Will it be too much and make the room sound totally dead?!

2. If I build the whole rear wall bass trap, would it entirely eliminate the need for absorption on front wall? Using REW's room simulator, after entering in .9 absorption on the rear wall, up'ing the absorption value on front wall makes almost no difference.

I think a goal of getting all frequencies below 250ms decay times at 100 db would be pretty good. Lastly, I have not done any EQ'ing yet. I have an Onkyo TX-NR818 on order, and I'll set up the audyssey xt32 with that.

EDIT: 3rd Question: I had planned on doubling up all first reflection absorption panels to make them 4" thick...but after seeing my decay times, I wonder if spending my time/money only on the back wall is a better idea, yes?

2nd EDIT: My biggest problem, the 45Hz spike, appears to be a front to back related problem. In the room simulator, creating higher absorption on the rear wall kills that spike pretty quickly.


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## bpape (Sep 14, 2006)

I would want to know what's coming off that back wall first. Try moving the mic forward a bit and see what changes in the frequency response below 200Hz. 

The point of the front wall is to absorb reflections from the surrounds much moreso than changing general decay times.

Doesn't look like you need much more mid/high absorption so I'd use some sort of facing on the rear wall to block mids and highs getting in but still passing lower mids and bass.

Bryan


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## Patzig (Oct 10, 2012)

Hmm, thanks for the reply Bryan. I see your point on the front wall absorption. And I'll move the mic forward/backward to see what changes as well when I get home. Good thoughts for sure. 

I've seen you talk about facing on bass traps before. For my room, what material would you possibly recommend? Would simple paper be too thin for mid bass? Thank you for your help.


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## bpape (Sep 14, 2006)

It all depends on how low you want to start blocking things. Paper facing will start to reflect maybe around 1k. Pool liner maybe 500. 1/2lb MLV, about 250. 

Bryan


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## Patzig (Oct 10, 2012)

I see. If I went with MLV that'd probably cost more than than R-30 to fill up the back wall lol.


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## bpape (Sep 14, 2006)

Could be. Pond liner is probably your best bet as a compromise.


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## Patzig (Oct 10, 2012)

Red - 44" from back wall (This is close to where I sit now)
Yellow - 50" from back wall
Green - 56" from back wall (This is 38% from back wall)
Blue - 62" (this distance comes out the smoothest FR)

Everything above 300 Hz got weird at the different distances because my 1st reflection panels became out of alignment as I moved the mic forward.


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## sdurani (Oct 28, 2010)

Patzig said:


> My biggest problem, the 45Hz spike, appears to be a front to back related problem.


45Hz is your first length mode. Could you place your sub at the midpoint of room length and make one more measurement?


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## bpape (Sep 14, 2006)

Think I'm liking 56" from the back better. While it does not bring the first peak down as far, it also does not introduce some of the nulls the other one does.

Bryan


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## Patzig (Oct 10, 2012)

sdurani - The sub weighs ~130lbs and there's a ~100 lb center channel sitting on top of it. I think I'll just stick with the mic placement adjustments lol. But maybe I'll feel not lazy when I get home and try it out.

So, moving my seating up to 38%, building whole wall bass trap, and audyssey from Onkyo 818 should get me pretty close!? I'm down. I think I'll build the wall and leave it "naked" at first. If it's absolutely dead, I'll try some pond liner to cover it.


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## sdurani (Oct 28, 2010)

Patzig said:


> sdurani - The sub weighs ~130lbs and there's a ~100 lb center channel sitting on top of it. I think I'll just stick with the mic placement adjustments lol. But maybe I'll feel not lazy when I get home and try it out.


No problemo, I was just suggesting a location that could cancel the 45Hz mode.


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## FOH (Aug 27, 2012)

Furniture sliders could help things, ... felt for hard flooring, and the hard plastic ones for carpeted flooring. Every hardware store has them, I wouldn't want to be without them. The ability to move both the source and the LP/measuring position, is a powerful tool in one's arsenal. 

I'm sure bpape, and sdurani would agree, that acoustics in general, and more specifically small room acoustics, what yields results and what doesn't can be counter-intuitive. Oftentimes, despite the sizable wavelengths involved, even modest subwoofer movements can elicit significant response changes. 

Best of luck


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