# My almost cube room



## GuitarCry (Dec 14, 2008)

If I believed in god I would thank him for this community. Unfortunately, I can only thank you for your help.

I'm trying to figure out what are the most cost/time/effective changes I can do to my listening room to improve it's acoustics. 
It's for stereo music listening, but unfortunately it's almost cube (see picture) and has the outstanding volume of 39m3!



The speaker position follows the golden ratio rule and the toe-in is focused on the rear wall center, behind the listener

The room is too *boomy and fluterry*. I've recently build and installed 6 DYI high-density extruded polystyrene skyline acoustic diffusers as you can see in the (bad panoramic, taken from the door) picture below. I know that their placement is far from ideal, but was the best I could do considering the room and WAF restrictions :sarcastic: 


I did REW measurements before (in blue) and after (in red) the diffusers with the following system
*Audio system*: Monitor Audio BR2 powered by Cambridge Audio 740A
*Measurement system*: Behringer ECM8000 (at listening position, vertical with 15º tilt forward), Behringer UB802 mixing table and Creative Labs USB Sound Blaster Live!​
*1/6 Octave Smoothing - [20Hz, 20kHz]*

*
1/48 Octave Smoothing - [20Hz, 200Hz]*






I was surprised by what seemed to be a improvement in the [100Hz, 120Hz] blue depression seen above, although the diffusers should theoretically only work on the 525Hz-4290Hz range :rubeyes:

I'm a newbie here, but I would say my too-long decay and boom at [130Hz, 250Hz] are my room's biggest faults... right!? 

I'm planning on building 3 (cannot block door) floor-to-ceiling corner superchunk triangular bass-traps, of 30cm side-length (WAF will not approve 60cm) using rockwool and the supernova tips

I'm also planning on filling the speaker stands with the same rockwool for bass-trapping.


*Questions*

 Any tips on what probably are the changeable variables in my room that will yield the greater improvement?
 Is the Superchunk the way to go?
 I can buy cheap rockwool for the bass-traps with 70Kg/m3. But I can also obtain 145Kg/m3 at a much higher cost. Which should yield the better performance for my case?
 Is there any equation for estimating SuperChunk corner triangle bass trap frequency dependent absorption?
 Putting a Bass-trap on the left of the system and not on the right (door there) will probably produce some imaging distortion. But I'm guessing the benefits will justify... what do you think?

An Alleluia to this wonderful community.

Cheers


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## bpape (Sep 14, 2006)

My guess is that something else has changed. Even moving the mic position a few inches on the before and after can change things. I'd agree that those diffusers won't do anything down at 100Hz.

If the door on the right is usually open, you can do chunks in the left front corner. I'd also do some thicker treatment on the wall directly behind you.

For thicker treatments, the lighter weight material will work just fine.

There is not perfect way to calculate corner absorption. It's not really 100% understood hence is not allowed as a standardized mounting method for lab measurements. In general, bigger is better. 

You also have a symmetry anomaly with absorption (curtains) on the left and no absorption on the right (Solid wall and cd rack).

Bryan


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## fitzwaddle (Aug 25, 2010)

Not an expert by any means - but I have read the Acoustic Treatments master thread on AVS Forums *twice*, and took some notes. :nerd:

Looking at the graph peak, bass trapping looks like a good idea, and superchunks are effective. Not sure on the unit conversion, but took note of this: "703 at 3 pcf is pretty much the standard for mid and high frequencies. Denser 705 at 6 pcf is better for bass trapping when using thicker panels mounted straddling the corners." and "AT LEAST 4" - 6" is better if you want to get some bass control."


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## bpape (Sep 14, 2006)

For < 4", 705 is a better choice for bass control. For 4" -6", 703 is as good or slightly better. For chunks, 703 will actually perform considerably better and you can go even lighter density. It's all about gas flow.

Bryan


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## fitzwaddle (Aug 25, 2010)

Thanks for the clarification - another quote to file away. :T


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## Audiolabs (Mar 25, 2009)

Hi "Cube": Your room dimensions are stacking axial modes at 106, 130, 143, and 150 Hz. This is consistent with your impulse response as you can see a lot of energy in first reflections. The decay time seems quite long. You can combat these in a couple of ways. The best way is to change dimensions. For example, are you willing (and would it meet your WAF criteria to adjust the ceiling dimension to 2.74 meters from the stated 2.81. This may at first seem radical, but it is really only 7 cm's and could be done. This small difference would optimize your room dimensionally and allow the modes to increase across 3rd octave bands (that's a good thing). It will nullify most of the comb filtering and should tighten up the low end. Next, why did you choose diffusion first and how did you calculate the locations? I would suggest removing the diffusers (except the ceiling) and moving ahead with your corner traps, but try to avoid polyurethane foam products and use fiberglass. The I would attempt to deal with side wall and ceiling reflections using absorbers (although the ceiling diffuser properly placed might work really well). Then I would calculate a suitable position for the diffusion.
Also, I agree with the other poster when he suggests that the results of the post diffuser measurement show big changes. This is almost certainly not directly related to the diffusers but to another change. It could be a simple as mic placement.
Good luck. I'll watch this post to see how you make out.

Jim


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## GuitarCry (Dec 14, 2008)

Thank you all for your generous 5 cents, which are worth millions to me



> My guess is that something else has changed. [...]
> Also, I agree with the other poster when he suggests that the results of the post diffuser measurement show big changes. This is almost certainly not directly related to the diffusers but to another change. It could be a simple as mic placement.
> 
> Read more: My almost cube room - Home Theater Forum and Systems - HomeTheaterShack.com


Yes. Indeed as you may guess from the room scheme, that speaker placement kind of blocks the room entrance. When not in use, speakers are moved against the wall, hence is virtually impossible to reproduce the exact speaker position. That and the mic, should attend to the bass change between measurements.



> thicker treatment


By thicker treatment are you referring to absorption or diffusion? Bass, mid, high or full range? I probably could get some material behind those backless shelf's (see picture), but exposed treatment would have to go through a very tough WAF evaluation. 



> For chunks, 703 will actually perform considerably better and you can go even lighter density. It's all about gas flow.


Really!? That is nice to know. So, what would be a recommended rockwool density for a triangular 30x30x21cm superchunk? 70kg/m3? More? Less?



> For example, are you willing (and would it meet your WAF criteria to adjust the ceiling dimension to 2.74 meters from the stated 2.81


Yeah, I thought of that. Unfortunately, besides the WAF factor, budget is also an issue. I thought of doing a lot more ceiling diffuser (all of the 6 were supposed to be there), so the medium room height would be lower, but due to it's unevenness (not a straight ceiling) I could only glue 3, and the other 3 ended up in the side walls according to WAF criteria. Maybe I could build some 7cm bass-trap panels, and apply them around the ceiling diffusers. That might be WAF wise possible. Would that work in your opinion?



> but try to avoid polyurethane foam products and use fiberglass


Yes, I plan to use rockwool. Just need to get the right density for the job.



> I would attempt to deal with side wall and ceiling reflections using absorbers


I would to. Unfortunately, considering my first reflections, on the left is a window (cannot cover it besides the curtain), on the right is a CD shelf (which I "unaligned" to somewhat diffuse), on the floor is a carpet, on the ceiling are the skyline diffusers, on the back that painting is unmovable (WAF criteria), somewhat breathable and has Thinsulate behind it.... what to do :dontknow: Just the front wall (behind the speakers) is currently naked and could more easily be treated.


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## bpape (Sep 14, 2006)

Surface area is critical as is thickness. Thicker to me means minimum 4". 6" is better.

Yes - at > 4", 703 is actually better than 705 and at 1/2 the cost.

Bryan


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## GuitarCry (Dec 14, 2008)

I know that it all depends on material, thickness and area, but are you saying Bryan that you would start applying thick absorption panels in my room's back wall before going into the superchunk corner bass-traps?

I know that this room needs a lot of work before it is acoustically decent, but I want to focus my time, energy, money and WAF tolerance in the most beneficial variables.

Cheers


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## bpape (Sep 14, 2006)

Not saying that at all. Just identifying it as one of the more important things to move up the priority ladder. Since you're going do DIY anyway, it's easy enough to wrap 6 pcs of 2" 703 in a blanket or a sheet to form a nice 4'x4'x6" thick test panel to try on the back wall. Then you can do the same thing with 2 2'x4'x6' panels to lean straddling the corners to simulate the chunks. 

At least that way, you'll have tried both and will be able to measure and see which does what for you and decide for yourself which one you want to start with.

Bryan


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## DanTheMan (Oct 12, 2009)

Can't wait to see what happens here. The room I'm working on is a cuboidish one.

Dan


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## GuitarCry (Dec 14, 2008)

@Brian Pape: Hey, that's a good idea. I'll do just that. I'll post the results with those 2 test-sets during this week. Just need to find the best place to buy the rockwool. 

@DanTheMan: Welcome to my nightmare Dan. I hope the room your working on is not yours, or at least not your only choice for personal listening space.

Cheers


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## DanTheMan (Oct 12, 2009)

My room's not as cube-ish as yours, but it's fairly close. My bass decay is considerably easier to work with, but my FR in the bass is worse. I've just got one huge bump at 45Hz and some ripple between 100-200Hz. The 45Hz issue won't be fixed by absorption, but the 100-200 should be possible to a greater degree.

As far as the sound goes, I'm loving it now. You can make them work. That said, I am going to try to improve it with diffusion after I get back from a needed vacation.

Good luck!

Dan


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