Calculating Room Modes - Odd Shaped Room

**Bob in St. Louis** · **02-09-07, 12:10 PM**

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

**bpape** · **02-09-07, 12:22 PM**

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

**Bob in St. Louis** · **02-09-07, 01:01 PM**

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

**basementjack** · **02-09-07, 03:50 PM**

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.

**Bob in St. Louis** · **02-09-07, 04:39 PM**

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

Thanks

Bob

**Bob in St. Louis** · **02-10-07, 11:13 AM**

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

**bpape** · **02-11-07, 11:32 AM**

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

**basementjack** · **02-11-07, 02:35 PM**

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

**Bob in St. Louis** · **02-12-07, 11:49 AM**

Quote:

bpape wrote:

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

**Ethan Winer** · **02-12-07, 02:48 PM**

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

**Bob in St. Louis** · **02-12-07, 03:13 PM**

Ethan, Thank You for responding.
I've downloaded the tones and graphs from RealTraps (pretty cool place, you may have heard of it.

)
I ran the tones and charted my graph. I got peaks and valleys just like you'd expect. Now, as an acoustic newbee, "Now what". Do I buy a BFD and adjust the drivers, or do I treat the room.
I went with the room treatment as my next focus. I put some effort into the ceiling with the "creative use of drywall", and 2X2 USG tiles.

Here's a few pics to give an idea of where I'm at.

http://home-and-garden.webshots.com/...85868784vDKZlv
http://home-and-garden.webshots.com/...85868784qhgfBg
http://home-and-garden.webshots.com/...85868784ojxTgA
http://home-and-garden.webshots.com/...85868784SNqObr

Thanks guys
Bob

**brucek** · **02-12-07, 03:28 PM**

Quote:

I've downloaded the tones and graphs from RealTraps (pretty cool place, you may have heard of it. )
I ran the tones and charted my graph.

Are you aware of a much more accurate way of plotting room response called REW.....

**bpape** · **02-12-07, 04:55 PM**

Ethan.

Bob's room will also be used for 2 channel listening so we'll want to be a bit more ginger with the treatments.

Bob,

EQ will help some - AFTER you deal with the room itself. I personally would only run EQ on a sub and not the mains. Treatment will help with FR and also get decay times in line. EQ is only for the last few stubborn peaks - and won't do anything for nulls.

Bryan

**Bob in St. Louis** · **02-12-07, 04:57 PM**

Bruce, I've pondered that.
But was intimidated at the thought of purchacing a piece of equipment who's capabilities are far beyond my level of understanding.
Also, a few more questions;
From what I've read, it only does subs? No fullrange?
I've heard varying opinions on whether or not open baffle should even have in room measurements performed on them.
I've thought about the BFD EQ, but have not found any info on whether or not it can handle:
(2) OB Front Mains (powered by H/K receiver)
(2) OB Front Main Subs (mono from plate amp)
(1) "Traditional" sub (bridged mono from 2nd amp)

Lots of questions. Unfortunately, I think this is one of those situations that the more I learn, the more questions I'll have. Basically, at this point in time, I'm not intellegent enough to know what questions to ask.

All help is very much appreciated.

Bob

**bpape** · **02-12-07, 05:00 PM**

Bob,

If you can wait till things calm down a bit, I'll be happy to come over and we can take some measurements. I have REQ and the necessary mic/pre/USB interface for my laptop.

Bryan

**Bob in St. Louis** · **02-12-07, 05:12 PM**

Quote:

bpape wrote:

If you can wait till things calm down a bit, I'll be happy to come over and we can take some measurements. I have REQ and the necessary mic/pre/USB interface for my laptop.

Wow, you guys are great.
Between Jack, Ethan, Bruce, and Bryan I feel all warm and fuzzy inside.
Bryan, The OB's are sounding better than the last time you heard them.

Thanks guys!
Bob

**basementjack** · **02-12-07, 08:55 PM**

Hey Bob, I looked at those pictures, and just based on experience it looks like you should have a pretty decent sounding room on your hands.

I agree with ethan, in that an acoustic model of your room won't reveal as much as an actual measurement, and I think for some reason when we started this discussion I must have been thinking this was an unfinished space.

rew is not too hard to use, especially with the latest version...
I'm sure once you see Bryan use it- you'll be able to pick up on it.

Not sure if Bryan has demo panels lying around- but it would sure be cool to be able to measure your room before and after treatment - even he takes the panels home with him.

as far as purchasing - REW is free, but you do need a sound card and a microphone.

Your soundcard needs a line in.
if you have a radioshack SPL meter, you can use it as the mic.

So you may already have everything you need...

**Bob in St. Louis** · **02-13-07, 08:19 AM**

Thanks for the complement Jack. Being a sonic "no-nothing", I tried to build the room (ceiling mainly) with sound waves in mind. Kind of like, "If I was a wave, how would I react to this ceiling?" That's why it's so oddly shaped with all the angles. I tried to break it up as much as possible.

I've got a digital RS SPL meter. Also the receiver I've got came with it's own mic too (with a VERY long cord

), that plugs into the face of the receiver for doing it's own version of "Auto EQ"/In-Room-Measurements". Someone told me that it wasn't designed/programmed for dipole bass, and that maybe throwing it off....

I'll have to check my soundcard for an input. I would think any modern PC would have a mic input because of the voice "stuff" you can do with various software nowadays. The PC came with a voice mic, I've just never had a need for it. I would think it was designed to plug into the sound card, but I'm not sure.
(And no.... I'm not thinking of using the PC's factory mic to do room measurements)

Bob

**Ethan Winer** · **02-13-07, 06:39 PM**

Bob,

> "Now what". Do I buy a BFD and adjust the drivers, or do I treat the room. <

Treat the room! EQ is a last resort, used only if you've put in as much treatment as you can stand to look at and you still have a problem. A problem that EQ can help with, that is. EQ will not help with early reflections, nor above the subwoofer range.

> Between Jack, Ethan, Bruce, and Bryan I feel all warm and fuzzy inside. <

Yeah, well just wait until you receive our bill.

I kid!

--Ethan

**Bob in St. Louis** · **02-14-07, 06:58 AM**

Quote:

Treat the room! EQ is a last resort, used only if you've put in as much treatment as you can stand to look at and you still have a problem. A problem that EQ can help with, that is. EQ will not help with early reflections, nor above the subwoofer range.

Good points Ethan. I understand.

Quote:

Between Jack, Ethan, Bruce, and Bryan I feel all warm and fuzzy inside.
Yeah, well just wait until you receive our bill.

I kid!

It's ok guys, no problem at all. I'm indepenantly wealthy.

I kid too!

Bob

**Bob in St. Louis** · **02-18-07, 10:56 PM**

How about killing three of four birds with one stone?
I've been kicking around this idea for a few months:

http://www.audiocircle.com/circles/i...?topic=37252.0
Regarding the Thuneau software.

Very quick overview, it's a PC based software that measures FR of the entire systems output (room included) and you can adjust XO, phase, and EQ ON THE FLY. Literally.

Any thoughts?

Bob

**bpape** · **02-19-07, 08:00 AM**

It'd be great - if you don't mind running all your signal through a PC.

If you're running a SB for your source, there are Room EQ plugins that work with it on the Slim Devices SB forums. For other sources, I wouldn't run them back into a PC. A BFD just for the sub would be a much more friendly solution.

Bryan

**Bob in St. Louis** · **02-19-07, 08:15 AM**

Hmm, decisions, decision, decisions....

Bryan, I'm not using a SB. Presently running MS MSE to the XBox360 as the 'extender'. Works pretty well.
I've thought about putting the PC in the rack system with the rest of the equipment in the hope that someday it'll be a HTPC. I was thinking this would be a step in the right direction. Although I'm unfamiliar with the capabilities of a SB (and the full capabilities of the Thuneau software for that matter) they both look pretty sharp to me.
As a newb to the whole FR/XO thing, I figure if I had the ability to quickly "undo" any wierd adjustment/settings I may have done, I'd be able to tweek easier and faster.

Bob

**Ethan Winer** · **02-19-07, 04:23 PM**

Bob,

> Very quick overview, it's a PC based software that measures FR of the entire systems output (room included) and you can adjust XO, phase, and EQ ON THE FLY. Literally. <

I looked at that site and I couldn't figure out what the point is supposed to be. Why would I want to adjust any of that at all, let alone in real time?

--Ethan

**Bob in St. Louis** · **02-19-07, 04:54 PM**

Quote:

Ethan Winer wrote:

I looked at that site and I couldn't figure out what the point is supposed to be. Why would I want to adjust any of that at all, let alone in real time?

Really, I would think it'd be the ultimate in adjustability. Play a given tone at a given Hz/SPL and you could tweek it "at will", whenever your heart desires. All at your fingertips. I realise it add gobs of wiring, but I'm not one of the "K.I.S.S." type of guys who simply has a front end, tube amp, and speakers.
I understand why it woudn't be someone's cup of tea, but I'm puzzled why a fellow wouldn't want that.
What am I missing Ethan?

Bob

Advertisement