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Why "splay" walls 4 custom listening room design?

I'm currious if some of the more informed and experienced audio guys out there can shead some light on this one, or at least add some input? I have been reading some posts on this sight, and others regarding "splaying" walls for better sound in general from a room. I've been in the process of designing a room from scratch, and have some issues of strong doubt regarding the benefits this would hae for my custom listening room. I plan on doing both extensive home theater and 2 channel music listening in the room, and want to design it with the best dimmensions and acoustical attributes and treatments possible.
I have been an avid reader of the Home Theater Architect in Stereophiles Home Theater Magazine since it started, and personally share a lot of the system set up and room design and acoustical approaches that that collumn preaches. Infact I believe the writer of that Article bills himself as the best designer in the business, with the best credentials, and supposedly he designed the Disney Imax venue at Disney world. So it sounds like he knows what he's doing, and is respected and experienced quite well for me to want to believe what he teaches I suppose.
I have also other info from other sources I've acquired over the years, and just don't see what, if any, benefit I would derive from actually designing a room with "non parallel" surfaces. I know I've heard on at least a few occasions on this web site that I've heard people recommend doing the "splayed walls" thing, but I have some questions. If non symetrical splayed wall rooms is the answer for smoothing out bass anomalies more evenly, and taking care of slap echo (which I understand), then how can you expect to get any semblance of symetry with regards to both the speakers and the listeng seats, in a multi seating set up?! My vision of this is that there would have to be speakers in some rather random and non symetrical placings to get good sound overall, and would this be practical for convenience? but what about getting everything symetrically layed out for the overall pressentation and balance with a possible projector screen or monitor, as well as other possible listeners in the room?
It just sounds rather random and non uniform. I am also inclined to believe that having more than one seat in room like this would cause me to have to place chairs all around the room in some rather scatered patterns and placings due to the more random nature of the sound in a more trapezoid shaped splayed walled room. I think in a more symetrical shaped rectangular kind of room I would at least be able to predict what was going to sound like what in different symetrical seating possitions, and I could make things neater and more organized from a design and astetic standpoint, I guess.
Any other input would be appreciated. Does anyone here have any experience with splayed room design? I was once in a room at a local audio store which did a room with splayed walls, and didn't see what the bid deal was. But then I'm new to doing anything this ambitious.
Thanx for any input.
wooterb
tireguy
1,964 posts
 
Clueless-good post but I got it the first time ;) j/k

But he is exactly right on, the frequency humps a room with a less then perfect size can impart on a system is very noticeable. I spent some time recently at Rives site and it was really an eye opener and I feel it was possibly the best time I have spent online in a while- very informative and explained in english! The formulas that Rivesaudio gives is VERY helpful and simple to use, I would recommend any one trying to optimize there system read his remarks and follow as closely as possibly. I know Bill E.(Lakefrontroad) is having his room designed and built and he is going all out and it should be really interesting when it is done, no parrellel walls at all. It is amazing what a difference a room can make or what a difference you can make on a room!
phild
603 posts
 
It's standard in recording studios (when they're designed as recording studios that is...not just a bsement with some mics)...not two walls should be parallel or the same length.
rives
953 posts
 
Wooterb, first I should comment on Russ H. HT home theater architect. Just because he designed IMAX doesn't mean he is qualified for small room acoustics--they are very different. The fact is Russ H. is very qualified for small room acoustics, but my point is, don't take someone that has done studios and theaters as an expert in home theater or small listening room applications. Small rooms (less than 8000 cubic feet) for home listening and HT are very different animals--but the tools of the trade are the same. In fact we are redoing some rooms that were done by studio engineers--they were perfect for studios, the reverb times and everything are right on--but they sound terrible for home listening.

Now on to your real question: splayed walls. Two parallel walls will produce room modes. Some of these modes can have very high Q factors (they are narrow band and highly peaked). When you splay the walls you don't eliminate the mode, but you distribute it. The Q factor goes down as does the peak. The more the splay the lower the Q factor, until at some point there is basically very little left of a room mode. Splaying walls if very effective in this matter.

Why don't people splay walls? It's costly. It doesn't work that great for the resale value of your home. It is "unpredictable". The last statement is not at all true, but has been quoted from Alton Everest and others. He also doesn't believe splaying is very effective: calling it nominal--but I disagree here as well. (Everest's books by the way are still excellent--I just don't agree with everything in them) Splaying the walls is very predictable, but the math is much more complicated and not easily described. If you do intend to splay the walls, it's a good idea to work with an acoustical engineer and make sure it's right. I don't recommend most people to go the splayed wall route alone.

A comment on the golden triangle: Most of the previous work in our opinion is not quite right. It evenly weights axial, transaxial, and oblique modes. Oblique modes are almost negligible and axial should have 3 times the weighting factor of the transaxial. We are working on new ratios and new methods that better distribute actual real world results. We are not done with this work yet, and still take each room as a case by case basis.

As to Bill E. room: It will be fantastic. Bill is fortunate enough to be able to spend what is necessary to build this room (in an existing house no less- far more expensive than new construction). There are no parallel walls save one in the rear which is such a small surface area it is negligible. It is designed for 2 channel only, and the difference in design for 2 channel vs HT is pretty great. We are very anxious to get this room complete--and listen.

Please do visit our website at www.rivesaudio.com. It has been mentioned and the tutorial in the acoustical issues section should be helpful.
jadem6's avatar
jadem6
1,074 posts
 
As an Architect of high end residential, I've had quite a few opportunities to design/ build and research the room issues. Two years ago my client spent quite a bit of money ($15,000) having an acoustics expert calculate his $200,000 home theater needs. This guy designs home theaters, small scale preforming arts facilities, movie houses and churches.
In home audio our needs are unique in that the scale is very small, reverberation rates, sound enhancement and echo are nominal issues. This could possibly be what Everest is discussing. Our issues are mostly side wall and floor/ ceiling first order reflections (slap echo) and frequency exaggeration.
A very small splay (narrower at the front) will alleviate most of these frequency nodes, but some thought could be put to the amount of splay. Too much could reinforce the projection and act as a "horn" and not enough will not achieve the intended goal. Ceiling and floor sloping can be more dangerous, in that the sound angles off a sloped ceiling (in the same fashion as the walls) could end up directing the reflection bach to the listener (especially with multiple seating locations). Think of a dome, it reinforces all sound to the middle, very bad in our situation. A slope down the axis of the room however could disperse the reflections very well.
The consultant we used had a very elaborate computer program that he was able to model the full spectrum of possibilities for the best solution. He was able to produce an audio track for any position in the room to determine what every seat would hear. There are cheaper programs available that could do some of the same things, just not quite as involved.
The rule of thumb I would use is the ratios spelled out in Everest's books or Robert Harley's book to determine the best ratio and size. If you did splay the side walls, I would use the width recommended as the average (mid point) of the splayed wall. I have been using a 2 ½ degree angle on my designs with very good results. The ceiling I would vault if possible.
As to how important this is, it completely depends on how far your willing to go. If your intending to get every ounce from your system with power conditioning, cables and tweaks, then this makes sense. If your happy with 80% of perfection, skip it, it's not worth the hassle. If you do however pursue this I would recommend you look into what wall materials your using. One layer of drywall over wood studs can give a soggy base response compared to a more rigid construction. You might consider building in a true base trap in the design, what acoustic treatments are you willing to live with, if non then these issues become extremely important.
"Acoustic treatments are a band-aid for problems not addressed during design, not the answer" according to this expert.
cdc
1,807 posts
 
Wooterb, have you look into getting CARA release 2.1. This is supposed to be the best computer analysis software available and should give you some answers before start building. It costs about $50.00.
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