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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

Showing 4 responses by clueless

clueless
763 posts
 
A room reinforces certain frequencies that are dependent on the size of the room. There are a number of them but the fundamental two wall(axial)frequency that will be reinforced, for example, is found with this formula:1130/2L. where L is the length of the room in feet. 1130 is the speed of sound per second in feet.

If your room is 16 feet long the room's natural/resonant frequency between those two walls is 35.31Hz. The room will reinforce that frequency and multiples thereof. You want to avoid/tame this tendency to reinforce a single frequency and not others as it creates an unequal response. You also want to keep the resonant frequencies (and multiples thereof)of the other walls of the room from being the same becaue when this happens the resonant frequencies of each dimension of the room reinforce one another. That is why a square room(15x15)is said to be so bad.

One way to avoid this is to build with the "golden" ratios. Another sometimes used is to splay your walls. When you splay walls you cause the distance between opposing walls to vary slightly and, therefore, the walls do not reinforce just one frequency.

I know Rives(Abstract7) of Rives Audio is going to do this in his new room. Maybe he will pipe in. Others, like F. Alton Everest, think the effects are "nominal."(Master Handbook of Acoustics, p 281-282)

I remain,
clueless
763 posts
 
A room reinforces certain frequencies that are dependent on the size of the room. There are a number of them but the fundamental two wall(axial)frequency that will be reinforced, for example, is found with this formula:1130/2L. where L is the length of the room in feet. 1130 is the speed of sound per second in feet.

If your room is 16 feet long the room's natural/resonant frequency between those two walls is 35.31Hz. The room will reinforce that frequency and multiples thereof. You want to avoid/tame this tendency to reinforce a single frequency and not others as it creates an unequal response. You also want to keep the resonant frequencies (and multiples thereof)of the other walls of the room from being the same becaue when this happens the resonant frequencies of each dimension of the room reinforce one another. That is why a square room(15x15)is said to be so bad.

One way to avoid this is to build with the "golden" ratios. Another sometimes used is to splay your walls. When you splay walls you cause the distance between opposing walls to vary slightly and, therefore, the walls do not reinforce just one frequency.

I know Rives(Abstract7) of Rives Audio is going to do this in his new room. Maybe he will pipe in. Others, like F. Alton Everest, think the effects are "nominal."(Master Handbook of Acoustics, p 281-282)

I remain,
clueless
763 posts
 
Jadem 6 said > "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."

Make sure your dry wallers are generous in the use of screws. I had one person (who I consider fairly well informed) argue that the choice of stud/drywall and the screw schedule in the typical american room (fairly simple and cheap to implement from the start) was more important than most of the other exotic stuff combined. He also noted that this issue was almost never found in computer programs for room acoustics.

What you learned ones say to this?

Also, Wooterb: Rives does not need a defense from me but I think you came down rather hard on him. He clearly stated that Russ was qualified and given his site and answers here for some time I think he does more than "dable" in it.
I "dable." To tell a professonal that he is a "dabler" is a back of the hand thing. It's nice to have pros in the mix sometimes and I have seen a lot of them chased off forums this way never to return.

Cheers,

I remain
clueless
763 posts
 
Hi all:

Immediately below is a quote from my post above.

>>>Jadem 6 said > "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."

Me talking.> Make sure your dry wallers are generous in the use of screws. I had one person (who I consider fairly well informed) argue that the choice of stud/drywall and the screw schedule in the typical american room (fairly simple and cheap to implement from the start) was more important than most of the other exotic stuff combined. He also noted that this issue was almost never found in computer programs for room acoustics.

Well I got no response to my post (so here I try again) and since posting it I read Martin Collom's article in the October issue of AudioXpress. The byline of the article is as follow:

"Balance of treble and bass in your speaker system may have more to do with what materials were used in building your house than other factors-which is good news for audio amateurs" Martin Colloms 11/02 AudioXpress p4.

What are the "other factors"? Well how about the Theile-Small parameters which are usually touted as gospel?

Colloms says" "the entire low-frequency scenerio deserves consideration." as they "assume 2Pi space" and "really need rethinking."

He implies that the entire structure of T/S are faulty and that the underlying assumptions are based on the kind of house Theile lived in at the time he did his work....

""Theile confirmed to me that his seminal work on low-frequency alignments and design was based on 2Pi partly because thet studio building where he researched and listened was a relatively "leaky" timber structure."" Collom p 6. (Jadem6 is making sense eh?)

In any event, maybe my friend from my first post was right. The kind of materials chosen for your walls and the screw schedule is more important than, as he puts it, "the exotic stuff"... i.e. TS measurements and computer models.

What you think?

I remain
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