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Discussion Starter · #1 · (Edited)
I've got a somewhat large living room I'm trying to improve the acoustics in. The room is almost 21 feet wide, and 15 feet long. The floor is carpet and the drywall ceiling is 8 feet above the listening position, sloping up to 9'-6" in the front, above the mains.



I've played with a few sub placement options and believe it or not this frequency response graphs represents the best location I could find, approximately front and center. The sub is a BIC Audio F12. The mains are Pioneer FS52. The response was taken with both channels on, speakers crossed at 80Hz and no other processing.






The ETC information shows a *really* bad ceiling bounce in the first 5ms:


Holding a piece of mineral wool up there does help though:



Also a waterfall:



I can take more/better measurements as needed, I imagine this will be a fairly long, methodical process. I've built half a dozen 2" panels out of mineral wool but so far I've only installed the two shown in the top diagram, at the sidewall first reflection points.

I also realize now that 2" panels in the corners will do nothing at all at bass frequencies, so I will probably not hang them in the corners, but instead do thick foam wedges there.

How should I proceed in trying to fix this room? I've already moved the couch forward about as far as I'm likely to get away with, but I know its still not ideal. Is this large room a good candidate for multiple subwoofers? Or should I try to tackle these issues with more passive treatment options first?
 

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Every room is a good candidate for multiple subwoofers.

I'm no expert, but this is what I would try.

First do per channel sweep measurements without the sub. I think the suckout you are seeing is related to the left channel being close to the opening. Once you track down the suckout you can go from there.

The right channel being corner reinforced vs the left being open should probably be addressed. Compare the response of left vs right and go from there. I will guess you will want heavy absorbtion in the front right corner both for bass issues and to align the channels better. 2 panels meeting the corner at front and right wall would be a good test.

There has to be some control added for smoothing room decay. Chances are you will benefit from some sort of light absorbtion on the rear wall to the left and right of the mlp. This will lower room decay time while dealing with echoes across the room. Between the FRP panels and rear corners would be a good place for diffusion. The rear corners will benefit from traps. A 1' wide panel of 3.5" roxul straddling the corner is very effective and far less intrusive than full corner wedges.

I love it when people post good measurements! Good job.
 

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Agreed. Balance the right corner to the opening on the left side - then recheck the sub integration with different phase settings and potentially moving the sub some more.

Obviously also address your side wall reflections and the differences in gain from right to left that also happens on the right wall.

The other thing that will help the perceived sound is getting the seating as far from the wall behind you is feasible.
 

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Discussion Starter · #4 · (Edited)
First do per channel sweep measurements without the sub. I think the suckout you are seeing is related to the left channel being close to the opening. Once you track down the suckout you can go from there.
Here's left a right channels on their own, crossed over at 100Hz with no subs. Normally I run the fronts at 80Hz however.



The right channel being corner reinforced vs the left being open should probably be addressed. Compare the response of left vs right and go from there. I will guess you will want heavy absorbtion in the front right corner both for bass issues and to align the channels better. 2 panels meeting the corner at front and right wall would be a good test.
Sorry, my initial overhead diagram didn't do the best job portraying the room conditions. Actually neither speaker is really in a true corner. The below perspective might show the room better. The doorway on the front wall, nearest the right speaker is normally open as well.



There has to be some control added for smoothing room decay. Chances are you will benefit from some sort of light absorbtion on the rear wall to the left and right of the mlp. This will lower room decay time while dealing with echoes across the room.
Sorry again, not mentioned in the first post but directly behind and to the left and right of the MLP are windows with blinds. So my only treatment options on the back wall are directly behind the MLP. Here is initial ETC: (personally I find %FS much easier to read)



Placing a 2" panel behind MLP it really knocks down the 6.83mS reflection, although not sure how good of an idea this is.



The next major reflection seems to be from the ceiling, so I held a 2" panel up there and had a friend run a scan:



Quite a bit clearer it seemed. And the very first spike less than 1mS after the direct sound seems to be from the arm of the couch itself. I set a 2" panel on the arm and it went away:



Between the FRP panels and rear corners would be a good place for diffusion. The rear corners will benefit from traps. A 1' wide panel of 3.5" roxul straddling the corner is very effective and far less intrusive than full corner wedges.
Good to know, I may cut down these 2'x4' panels of 2" material to make 1' x 4" deep corner panels. Not sure yet how I'm doing diffusion on a budget.
 

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Again, I'm not an acoustics expert. (Bpape overrules anything I can offer. ;) ). I am on the cusp of being comfortable with giving advice.

Ok, much better pic of situation. Your sub may improve if the Space between it and AV shelf is increased slightly. Not sure this will be an issue when you add sub #2.

The right and left channels share a similar response, definitely related to the openings on either side of the room I'd say. Not the worst scenario, as balance is preserved.

I am used to reading ETC curves as db over time (relating to RT60). I look for a smooth decay with a sawtooth edge (no spikes.). The distance % graph is nice for locating strength and distance from reflections. My problem with the distance % graph is it becomes easy to treat all spikes after the impulse as evil. Early reflections are important for creating "intimacy" late reflections are required for creating "spaciousness." The ratio of early to late reflections determines "clarity."

So, I would ask, what aspects of your room are you trying to improve acoustically? If you kill all of the later reflections, you will have extreme intimacy (and clarity) if you kill all early and late reflections you will have a dead room.

If smoother FR is what you are after try treating the room as mentioned. Delete the front right corner traps of course. :). Poly diffusers are the cheapest (and least effective) followed by skylines then QRDs. QRDs are the most effective, but require room to integrate properly with listening positions. I have yet to experience any diffuser products in person.

I recommend buying a book and learning all these aspects for yourself. :) This one is excellent.
 

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If you can make the panel behind you thicker, that will help even more. What is not shown is what frequencies the reflections are happening at. A thinner panel won't address lower in frequency though if only space for one, there will be a point where no thicker is really going to help as the waves get much larger than the panel surface.

I would do what you can in the rear corners and also consider doing something over/in the windows behind you.
 
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