Square Room Acoustics - nib walls - AVS Forum
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post #1 of 14 Old 05-06-2012, 06:54 AM - Thread Starter
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Hi All

I have read the threads on square rooms, but unfortunately only for the first time this evening. The attached shows the layout of the room. it is 16.89' wide, 16.36' long (deep) and is 7.87' high at the back of the room, racking up to 12.13' at the front of the room.

The structure is on beams with timber construction joists / bearers being 3.6' from ground level (old concrete slab).

I am in constuction stage, timber frame built, but no sheeting yet. So I have some freedom to make some changes. The right wall is brick (back of original house), the other 3 sides are going to be cladded.

Window on the LHS (1800mm high window wall.)

The question really is: If I move the Sub to beside the future couch (where I show a MUS (music cabinet) will I dramatically improve the room.

If I build a nib wall to the right og the right speaker (I have sketched the idea in green, would that make any difference / improvement. I could put one to the right of the couch as well.

Any ideas / suggestions would be greatly appreciated.
LL
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post #2 of 14 Old 05-06-2012, 12:26 PM
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I got your PM. The only way to determine the best sub location is to measure your room's low-frequency response at high resolution while you experiment:

Room Measuring Primer
Subwoofer Placement

As for the short wall to the right, it's probably too small to have much effect at low frequencies. Such long waves will just wrap around it.

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post #3 of 14 Old 05-06-2012, 02:07 PM - Thread Starter
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Thanks Ethan, appreciate your input.

Ok, so the Nib wall will not rectanglize (if that is a word ) the room.

So in summary, build as is, then bass traps in corners. You have a distributor in Australia which is great.

Am I correct with the maths and your software, that the height of the room for calculations is 2.4m to 3.6m rake is an average of 3.0m then I add the 1.1m for the Floor (ply flooring) down to the Slab below (house is on piers onto an old carport slab 1.1m below)

Also, is their a particular material for the window wall (1800mm high x 3000mm long) which will help. Should it be a heavy material or light, so the Bass is dampened.
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post #4 of 14 Old 05-06-2012, 02:09 PM
 
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An interior wall will most likely Only modify the specular reflections above the modal frequencies.

Unless the wall is massive (as in near identical to the exterior walls - assuming they are massive), the exterior walls will still determine the modal distribution of the interior energy, and the interior wall will do nothing to substantially modify the modal behavior, which due to the square room with near identical dimension has multiple surfaces reinforcing the same modal standing wave frequencies and thus exacerbating the situation.

Thus, you must still determine a mixed strategy based upon listener placement relative to modal peaks and nulls, subwoofer placement, tuned resonant pressure based traps, and passive velocity based porous traps and the limited judicious use of EQ.

Thus, unless you are intending to build a full sized interior wall (as part of a larger strategy) in order to modify the symmetrical specular behavior in the room such that the primary listening position could be offset from the geometric center of the room and away from the modal nulls defined by the more massive exterior boundaries - a good strategy commonly employed in professional and studio deigns to avoid the modal nulls if you can afford the 'loss of real estate' - the wall will not help with the LF modal issues.
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post #5 of 14 Old 05-07-2012, 12:06 PM
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Quote:
Originally Posted by dps4fx View Post

Am I correct with the maths and your software, that the height of the room for calculations is 2.4m to 3.6m rake is an average of 3.0m then I add the 1.1m for the Floor (ply flooring) down to the Slab below (house is on piers onto an old carport slab 1.1m below)

Calculators like my own Graphical Mode Calculator are meant to help design a new space that's not yet built. For an existing room, measuring will tell you exactly where the problem frequencies are, with more accuracy. But even that isn't usually needed. No matter what you measure, the solution is more or less the same: bass traps, absorbers at reflection points, and optionally diffusers.

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Should it be a heavy material or light, so the Bass is dampened.

The best walls are lightweight because they let bass pass through to the outside. Lighter walls can also give some bass trapping as they vibrate in sympathy. This absorbs bass energy, though the walls need insulation inside for this to work well.

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post #6 of 14 Old 05-09-2012, 02:16 AM - Thread Starter
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Hi Guys, I thought of something and would love your input. The Right Wall - existing back of the house, it hasn't been fitted with ferring channel yet, so what if I built that wall at an angle, so back is the 5150mm as shown, but on the screen wall it is is 300 - 600mm more narrow. Taking into account the ceiling is raked, does that solve many of the probelems

Look at the attached.

Thanks for your input
LL
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post #7 of 14 Old 05-09-2012, 10:20 AM
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I don't see how making that wall angled will help anything.

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post #8 of 14 Old 05-09-2012, 06:01 PM
 
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What Ethan said...

Two scenarios.

If the wall is insufficiently massive to function as a modal boundary (which is the most likely scenario...), then all it will do is screw with the specular reflections above the modal frequencies without any significant effect on the modal distribution which will still be determined by the more massive exterior boundaries.

If the angled wall is sufficiently massive to modify the low frequency modal energy, all it will do is result in a more complex modal distribution requiring still more effort to measure and map said distribution.

Neither method is sufficient to address modal behavior.
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post #9 of 14 Old 05-10-2012, 06:51 PM
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Multiple subs is your best bet deployed in mode canceling arrangements. Above the sub region youll need some serious bass trapping, stuff that is effective down to the sub crossover frequency.

Acoustic Frontiers: design and creation of high performance listening rooms, home theaters and project studios for discerning audio/video enthusiasts.
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post #10 of 14 Old 11-13-2012, 04:02 PM
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Is a cube room bad for bass? According to Red Spade Audio, it's fine.

Anyone can confirm this? Will having 2 subwoofers in a cubed room make a good room?
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post #11 of 14 Old 11-14-2012, 05:40 AM
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Quote:
Originally Posted by Skylinestar View Post

Is a cube room bad for bass? According to Red Spade Audio, it's fine.

Anyone can confirm this? Will having 2 subwoofers in a cubed room make a good room?
Quote:
Originally Posted by Skylinestar View Post

Is a cube room bad for bass? According to Red Spade Audio, it's fine.

As the saying goes, there are lies, utter lies and statistics. Simulations involving just a few possibly-cherry-picked examples prove nothing.

IMO you are over-thinking the problem. If you want to know what your room does, do some measurements of your room. I know about the long-standing audiophile tradition of spending $1,000s on equipment and refusing to pay even one dollar ($1) for test equipment to see how that equipment is working. Time to break that mold!
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Anyone can confirm this? Will having 2 subwoofers in a cubed room make a good room?

These are the results of a study from Harman that talks about the possible benefits of using multiple subwoofers.

http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White%20Papers/multsubs.pdf

http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White%20Papers/AES_Preprint_8748_color_plots.zip

They show what seems to be a better example of how to study room acoustics with simulations. They did virtual testing of many times more different configurations.
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post #12 of 14 Old 11-14-2012, 08:29 AM
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Quote:
Originally Posted by Skylinestar View Post

Is a cube room bad for bass?

Yes, it's the worst shape possible. I can't speak for the graphs on that web site, but you need to see up to 300 Hz. Multiple subs might help, but the main problem is strong resonances that require bass traps to tame.

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post #13 of 14 Old 11-14-2012, 11:39 AM
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Quote:
Originally Posted by Skylinestar View Post

Will having 2 subwoofers in a cubed room make a good room?
As Nyall said in the post right before your's: the subs can be set up in a mode cancelling arrangement to mitigate some of the bass problems in a square/cube shaped room. But that only works up to the crossover point. For bass above that point, you can't re-arrange your speakers for mode cancelling because you need to place them for good soundstage and proper imaging. Hence Nyall's recommendation for "serious bass trapping" down to the crossover point.

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post #14 of 14 Old 11-14-2012, 03:23 PM
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Quote:
Originally Posted by Ethan Winer View Post

Yes, it's the worst shape possible. I can't speak for the graphs on that web site, but you need to see up to 300 Hz. Multiple subs might help, but the main problem is strong resonances that require bass traps to tame.
--Ethan

Actually, sitting in the middle of a round sphere would be worse rolleyes.gif
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