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Scott Horton, techht.com
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Discussion Starter · #1 ·
Hi guys:


Finally! I am squeezing the some time to finish my own theater. I am dimension constrained by a lot of architectural "issues". I do have double walls and will have double drywall wall assemblies and ceiling. Drywall is due to start in a week. The room will be 29'6" x 17' 4.5" x 8' 7.625".


I ran all the mode calculators I could find to look at the room modes. The one calculator (don't know the author) shows modes and nulls at the listening position. Th last one linked below shows I have several nulls as well as modes at my main 2 "center" (not actually centered) listening positions.

This link has the calculations from the mode calculators I could find (Bob Golds, Ethan Winers, and the unknown author)


I need to start to prepare for what I will need to tame the room. I had planned on installing the Audyssey Pro EQ system, so hopefully that will help with modes some.


What about the nulls? Stuck with them? Will bass traps help?


To complicate things, my room has doors on 45deg short walls in a front and (same side) rear corner. The other 2 corners are free for bass traps, as are the soffit areas running lengthwise. The soffit area of the rear wall is occupied buy a real soffit enclosing some HVAC so no good place there.


Can any guru's advise me on what it will take to treat this room in general? It is a multi-purpose room, one main row of seating, with some "overflow" seating on bar behind regular seating, these will rarely be used for movie watching.


Thanks,

Scott
 

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Any chance you can post a floor plan with measurements? We need some kind of a visual aid to help in providing constructive feedback. Any pictures of what you've done so far? Pictures are a good thing - the more the better
 

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Scott Horton, techht.com
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Discussion Starter · #3 ·
OK. I added a plan view but it's just the basics. It was an old plan and I quickly erased some things that didn't apply. It's rough but very close to scale. I have a 2000 ft2 basement and right now I have the other part of the basement "loaded" into the HT room so I can have it drywalled. I'd be embarrassed to post photos of the actual room right now. But as it's basically a rectangular box with stud walls and ceiling, there isn't anything the plan won't show. Only thing the plan does not show very well is a soffit that is about 4' front to back, and 13" tall that runs the width of the room at the rear.


Plan added to the list of files linked in first post, direct link here HERE


Edit: I also planned to add a false soffit made from 2 LVL beams across the centerish area of the room to mount the PJ from. This will be the same height as the rear soffit, and will isolate the PJ mount from the floor assembly above (Living room) where footsteps can cause PJ shake. From this I planned on finishing the room long walls with soffits that could easily be bass traps made to look like soffits.
 

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I'm travelling but can get back to you shortly. The calculators (all of them are wrong) in your case. They are predicated on perfect walls and rectangular rooms. You have neither and a few doors and windows thrown in to boot. Talk with you soon!


(I'm arranging a failure of the slide on the 810 we're installing in the Caribbean. I'm certain the fix will require your personal touch.
)
 

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Modal issues in the bottom octaves are best dealt with subwoofer(s) and seat positioning. Then if you still have problems dial in with a parametric equalizer.


I would think you are far enough away from the angled corners that their perturbations from rectangular are not an issue, but sliding doors are likely to be pretty good bass traps (leaks) regardless of what you have for double walls.
 

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Quote:
Originally Posted by GetGray /forum/post/16938001


The room will be 29'6" x 17' 4.5" x 8' 7.625".

That's not bad at all. Plus, it's just as important to make the room the size and shape you need and want. Bass problems are solved with bass traps, which you need regardless of the room's size and shape. And the point Dennis made is important too. All mode calculators assume "perfect" walls (and floor and ceiling) which is never the case. So you should avoid obvious bad dimensions like 10 by 10 by 20 feet. But otherwise, make the room the size you need and want.

Quote:
What about the nulls? Stuck with them? Will bass traps help?

Yes, bass traps will help. The more you have, the flatter and tighter the low end will be. It's that simple.


--Ethan
 

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Scott Horton, techht.com
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Discussion Starter · #7 ·

Quote:
Originally Posted by Dennis Erskine /forum/post/16939707


I'm travelling but can get back to you shortly. The calculators (all of them are wrong) in your case. They are predicated on perfect walls and rectangular rooms. You have neither and a few doors and windows thrown in to boot. Talk with you soon!


(I'm arranging a failure of the slide on the 810 we're installing in the Caribbean. I'm certain the fix will require your personal touch.
)

Thank you Dennis. Help much appreciated.


Email me re the 810 and I will help in every way possible.
 

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Scott Horton, techht.com
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Discussion Starter · #8 ·

Quote:
Originally Posted by krasmuzik /forum/post/16939894


Modal issues in the bottom octaves are best dealt with subwoofer(s) and seat positioning. Then if you still have problems dial in with a parametric equalizer.


I would think you are far enough away from the angled corners that their perturbations from rectangular are not an issue, but sliding doors are likely to be pretty good bass traps (leaks) regardless of what you have for double walls.

Thanks K. The only sliding door is a glass one to the outside. I know its a bad thing, but it's there and bricked. No good way to ride myself of it. I am considering a retrofit but anything I put there will be "leaky". FWIW, all the other doors in the room are planned to be flush, 1.75" mineral core mounted in exterior frames with weatherstripping and threshold.
 

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Scott Horton, techht.com
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Discussion Starter · #9 ·

Quote:
Originally Posted by Ethan Winer /forum/post/16942593


Yes, bass traps will help. The more you have, the flatter and tighter the low end will be. It's that simple.

Thanks Ethan. I had presumed that to be the case form other input you've given in the past. I had figured I would either build them in lieu of the soffits running lengthwise, or build the lengthwise sections of soffit so they are the bass traps. Then I have 2 room corners I can fit some 2' wide traps without much issue.
 

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Scott Horton, techht.com
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Discussion Starter · #10 ·
I will true up the plan drawings since the angled corner walls and ceiling appear to be more of an issue tan I origianlly anticipated. The original plan drawing I posted is fairly accurate. Dimensions and some details changed a little when I added the inner wall framing, and some minor changes in the wetbar area.


I am constrained to this room size by 10" solid concrete in most cases, large I beams in other places, or the sch. 80 6" steel posts tat support the beams. And the HVAC/WH equipment, and a full bath with plumbing part of the slab. Some things aren't practical to move around.
 

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Quote:
Originally Posted by krasmuzik /forum/post/16939894


Modal issues in the bottom octaves are best dealt with subwoofer(s) and seat positioning. Then if you still have problems dial in with a parametric equalizer.

I agree with what Kevin says, and want to emphasize it. Do not expect generic bass traps to help down this low. I've designed custom very low frequency resonant absorbers for special purposes, but tuning them precisely can be a major pain in the ass, and consume much time.


And as others have said, the mode calculators are pretty worthless, even if you have the perfect shoebox-shaped room they are based on.


- Terry
 

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The basic problem with room mode calculators is that they don't predict which modes will cause problems and which won't (except in the most trivial cases of the lowest axial modes).


They are useful for identifying particular modes after the fact -- once you have built and measured the room. But with lowest frequency resonances, there is way too much interaction with unknowables of the room structure. Walls vibrate at frequencies comparable to low frequency room modes, and not even the most detailed Finite Element Analysis can predict exactly how. The science of acoustics simply has not progressed far enough. I know because I read the new journals every month!



- Terry
 
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