[ScottMayo]

 Someone else would have to suggest casting for Brian Cheney; I want to stay on his good side.

I say BC plays himself...as does the RM/X....

[/list:u]

Well, so much for getting Julia Roberts. I don't think she'll play opposite anything prettier than her.

I mean the speaker, of course...

[JohninCR]

Consensus is that angled walls do indeed alter the modes - and make them harder to calculate and control. It's easier to be able to predict them and deal with them if the space is simple, and you're going to have to deal with them no matter what you do, so it's better to keep it all straightforward.

Scott,
I'm not sure what consensus that is, but with adequate angles between surfaces, modes can't exist.  To me, straightfoward is eliminating problems by designing them away.  Roof lines and vaulted ceilings have odd angles all the time, so the GC and drywall guys can do almost anything you can dream up.   If you are building a house in a hot climate with huge picture windows, you don't put them facing west and then have to deal with all the cooling problems it creates.  You change the design to eliminate the problem to begin with.

Of course, considering the nightmare you went through, it may make the music sound better in the fine room you have as a final product.

[brj]

I'm not sure what consensus that is, but with adequate angles between surfaces, modes can't exist.  To me, straightfoward is eliminating problems by designing them away.  Roof lines and vaulted ceilings have odd angles all the time, so the GC and drywall guys can do almost anything you can dream up.   If you are building a house in a hot climate with huge picture windows, you don't put them facing west and then have to deal with all the cooling problems it creates.  You change the design to eliminate the problem to begin with.

What design and modeling tool are you using that accurately predicts the acoustic properties of rooms with angled walls and other non-orthogonal boundaries?

Scott's statement did not imply that rectangular rooms were better, but rather that they were easier to model (semi) accurately and thus easier to design treatments to handle.

[ScottMayo]

I'm not sure what consensus that is, but with adequate angles between surfaces, modes can't exist.

Any closed figure creates modes. It doesn't even have to be closed: fire a wave at a flat surface in space, of any frequency, and a point on the wall gets a double dose of that wave (coming and going). That's a mode. Not a very relevant one, but it exists.

Yes, you can use complex wall shapes to put the modes and nulls in more convenient places, and it's possible to come up with a shape that has only minor nulls or peaks in the 20-20k range at the listener's position. At least I assume it is, I've never tried. Not much point: I'm sure that if I tried to get a builder to construct it, I would have needed a significantly larger budget; and if he screwed it up I would have gone mad trying to work out the necessary corrections.

This isn't to say that it's not worth trying. For years my listening environment was a complex two story space with a floating bridge loft in the center; the speakers were under the bridge. Angled ceilings, irregular openings, fireplaces, a real mangle of shape and form. The stereo system didn't sound too bad: it did kick up some bass frequencies a bit, and I had a bizarre resonance around 28Hz that I never did quite figure out. But it worked pretty well. What I have now works much better, though.

[JohninCR]

I'm not using any tool or program.  Modes result from reflections of waves between surfaces in a manner where the wave peaks combine resulting in reenforcement of the original output or where peaks combine with troughs to create a null.

While a golden ratio rectangle room might be ideal for a rectangle because it spreads the modes out in such a way as to minimize them overall, it is still not ideal because the parallel surfaces will support standing waves of various frequencies.  All it does is make the computer modelling easy.

Orchestras don't play in rectangular rooms for good reason.  I'm not saying any shape of 6 non-parallel sides will work because you need symmetry.  You also don't want to have a shape where primary first reflections are focused at the listening position.  Appropriate shapes for room have been designed for a very long time before computers.  They just don't fit very well into typical home floor plans.  A separate structure, however, is another matter.

[ScottMayo]

Appropriate shapes for room have been designed for a very long time before computers. They just don't fit very well into typical home floor plans. A separate structure, however, is another matter.

Well, go for it. I was working within constraints (house addition, property lines, max ceiling heights, budgets, contractor ability), and paid money for expert advice to fit my constraints. With less tight constraints, I'm sure it's possible to come up with a more ideal design. Designing a true theater would be a fascinatng project.

[youngho]

Perhaps you guys are arguing at somewhat oblique angles.

Scott Mayo seems to be describing modes as inclusive of comb filter effects, saying that the reflections of sound waves off any boundaries result in constructive and destructive interference at different frequencies, depending on the distance of the listener to the boundary and the original signal in question. I wonder if this might be overly inclusive, however.

John seems to be describing modes as standing waves formed between two parallel surfaces, i.e. axial modes, possibly neglecting that standing waves can also be tangential or diagonal. A pentagon room, for example, will have standing waves (for example, imagine a 5-pointed star inside the pentagon with each point of the star located at the middle of each segment of the pentagon, as well as another with each point in each corner).

It seems to me as though many concert venues (for example, the Village Vanguard, as well as many old auditoriums) have a horn at the heart of their design, in the sense that the performers are located in the narrower part of the "horn" and the listeners in the wider part. Also, complexities in the boundaries of the concert venue (seats on the floor, for example) make the room a very complicated comb filter, which can be beneficial. However, shoe box halls can be extremely pleasant, as many orchestra lovers know.

[ScottMayo]

I got a lot of email from curious well-wishers. Thank you, everyone, for the interest!

The room still isn't finished cosmetically - and the room is the reason why. I go in there with every intention of cutting trim and hanging burlap - but somehow I always end up turning the stereo on, and the next 4 hours disappear.  When I do get off the couch, it's to experiment with subwoofer placement. It's a really, really bad room for getting any work done.  

As a wrap up to the long tale - the Amazing Remote Control (30 touch sensors, tied to a radio transmitter) project failed, when I found out that putting 30 touch senstors on a small panel basically doesn't work. When I first powered it on, the sensors started firing randomly and the room went beserk - lighting flashing and fading randomly, stereo throwing itself on and off, random warning beeps...

I ditched it, got an ethernet-to-serial board, and now I control my room off my laptop, from a computer interface I wrote. Bonus: I can control the room from any computer in my house. This is great because I can schedule a shutdown, lights, stereo and all, when the kids need to get to bed.  

Sonically, this room *rocks*. I made a few adjustments, and imaging and detail is to die for. QSound music has eerie presence. The clarity is such that I found myself turning up the volume to levels I never even considered before. I'm even getting decent sub integration (which I thought would be a problem for a while, as the Earthquake sub is not very musical). I still plan to upgrade to a VMPS Larger pair at some point.

Come listen.

[JLM]

Providing a slight angle from parallel for opposite walls does help.  An old audio shop did that with just a pair of opposite walls by putting one wall on a 80/100 degree angle to adjoining walls and it seemed to help by breaking up resonances.

The symetrical layout in a rectangular room is the best understood, but why not try moving the speakers/listening position around to provide the maximum reverb time (maximum the distance for a reflected laser beam to hit the listener fired from the speaker).

Another idea is the old concept of making opposite walls vary from each other in material (one reflective, the other absorptive).