Calculating Room Modes - Odd Shaped Room - Home Theater Forum and Systems - HomeTheaterShack.com

Old 02-09-07, 11:10 AM Thread Starter
Senior Shackster

Bob

Join Date: Oct 2006
Location: St. Louis, Missouri, USA
Posts: 443
Calculating Room Modes - Odd Shaped Room

Thank you gentlemen for the calculators.
After an exhaustive search, I've not been able to determine modes for a NONrectangular room.
Specifically an "L" shaped room. More specifically, "L" shaped rooms that terminate in open hallways (no doors).
Realising of course, the calculations would have to stop at some point otherwise a fellow would be making calculations based on one entire floor of his house, he'd have to stop somewhere.
Question is,...where would you stop, and how do you calculate an "L" shaped room?
Basically, I'm looking for a DIY way to treat a room (decently) on a bit of a budget.

Bob
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Old 02-09-07, 11:22 AM
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Bryan Pape

Join Date: Sep 2006
Location: Wildwood, MO (St. Loui
Posts: 5,209
Re: Calculating Room Modes - Odd Shaped Room

Hey Bob.

Calculate each rectangle. You'll have those modes. Then calculate the combination of rectangles. You'll have those. In addition, you'll get odd tangentials and obliques that are basically impossible without ray tracing.

So, if you had an L, you'll have the front to back rectangle, just the L rectangle, the L plus the end of the main part rectangle. Hope that made sense...

Bryan

I am serious... and don't call me Shirley.

Bryan Pape
GIK Acoustics
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Old 02-09-07, 12:01 PM Thread Starter
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Bob

Join Date: Oct 2006
Location: St. Louis, Missouri, USA
Posts: 443
Re: Calculating Room Modes - Odd Shaped Room

Hey Bryan, thanks for responding. (and so quickly too!! )

No, Sorry I'm confused.
Check out the drawing.
The top pic is the room.
The bottom two are variations on what I think you're talking about. The colors are red and yellow, but the yellow is totally missing from the scanner. (it's the only color highlighters I've got here at work)

"1" and "2" are the ideas, the letters represent the individual calculations.
Can you tell me which one is correct please.
Bob

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Old 02-09-07, 02:50 PM
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jack

Join Date: Sep 2006
Location: Chicago Suburbs, IL USA
Posts: 369
Re: Calculating Room Modes - Odd Shaped Room

Hey Bob, send me a PM and remind me,
and send me the exact measurements of the room, including height, and if that hallway goes far, send me the depth of that.

I'll enter this into Cara this weekend and let it do the modeling.

I've been meaning to learn Cara better so this will be a good opportunity.

- Jack
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Old 02-09-07, 03:39 PM Thread Starter
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Bob

Join Date: Oct 2006
Location: St. Louis, Missouri, USA
Posts: 443
Re: Calculating Room Modes - Odd Shaped Room

Hey Jack, that'd be very cool!
I'll get out the 'ol tape measure and give you some numbers this weekend.

Thanks
Bob
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Old 02-10-07, 10:13 AM Thread Starter
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Bob

Join Date: Oct 2006
Location: St. Louis, Missouri, USA
Posts: 443
Re: Calculating Room Modes - Odd Shaped Room

Ok guys, here's a quick sketch of the floor plan (without being too retentive with the graph paper).
The lines are not to scale, but the measurements are pretty accurate.
The darker lines are "the sounds wave boundry lines" so to speak.
I may have given too much information and cluttered it up a bit, but here goes:

Thanks for your time and effort!
Bob
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Old 02-11-07, 10:32 AM
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Bryan Pape

Join Date: Sep 2006
Location: Wildwood, MO (St. Loui
Posts: 5,209
Re: Calculating Room Modes - Odd Shaped Room

You'll get a combination of mode from the 21'3 x 21 area, 21x7'3, and 21'3x12 in axial modes. You'll also get a bit from the long hall down to the end but that will be somewhat muted. The fun comes with the tangentials and obliques.

I'll be interested to see what CARA does with this.

Bryan

I am serious... and don't call me Shirley.

Bryan Pape
GIK Acoustics
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Old 02-11-07, 01:35 PM
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jack

Join Date: Sep 2006
Location: Chicago Suburbs, IL USA
Posts: 369
Re: Calculating Room Modes - Odd Shaped Room

Hey Bob, I'm working on the floor plan now - I've got 30 min between afternoon activites!

- Jack
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Old 02-12-07, 10:49 AM Thread Starter
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Bob

Join Date: Oct 2006
Location: St. Louis, Missouri, USA
Posts: 443
Re: Calculating Room Modes - Odd Shaped Room

Quote:
bpape wrote: View Post
You'll get a combination of mode from the 21'3 x 21 area, 21x7'3, and 21'3x12 in axial modes. You'll also get a bit from the long hall down to the end but that will be somewhat muted. The fun comes with the tangentials and obliques.
I'll be interested to see what CARA does with this.
Bryan
Interesting for somebody that knows what the they're looking at!!
Yea, it will be cool to see what recommendations are made.

Jack, no problem. Take your time. Thank you for doing this, I'll owe you one.

Bob
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Old 02-12-07, 01:48 PM
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Ethan Winer

Join Date: Jul 2006
Location: New Milford, CT, USA
Posts: 251
Re: Calculating Room Modes - Odd Shaped Room

Bob,

Quote:
I've not been able to determine modes for a NONrectangular room ... Basically, I'm looking for a DIY way to treat a room (decently) on a bit of a budget.
You don't need a mode calculation to treat a room. That's useful only when designing a room where you have the chance to establish the dimensions. For an existing room you just treat it as usual. Here's my standard blurb about what all rooms need:

* Broadband (not tuned) bass traps straddling as many corners as you can manage, including the wall-ceiling corners.

* Mid/high frequency absorption at the first reflection points on the side walls and ceiling.

* Some additional amount of mid/high absorption and/or diffusion on any large areas of bare parallel surfaces, such as opposing walls or the ceiling if the floor is reflective.

Also, room mode calculations don't always tell you much useful anyway. Far better is to actually measure the room's response because then you know exactly what you have regardless of angles and "L" shapes etc. But you don't usually need to do that either.

--Ethan

Focal Press Book: The Audio Expert
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