Is there a benefit to adding splayed walls to this room?

Greetings, thanks for taking the time to read this. I am repurposing a room to be used as strictly a mixing room using nearfield monitors. No recording will take place in here, and isolation isn't a factor in this scenario. The existing room is a rectangle that measures 7.5' x 11.79' x 19.08' (HxWxL, giving me a ratio of 1:1.57:2.54) with the door on one of the narrow walls. Three walls are typical sheetrock on wood studs, the fourth wall is opposite the door and is cinderblock. I have a construction budget of $2000, and electrical and HVAC are non-issues in this question. Assuming I orientate the mixing setup long-ways, is there a benefit to building new 10% splayed walls on each long side? In your opinion will there be a potential reduction in flutter echo in the ~1700 sq ft room? Also assume that the four vertical corners will be trapped, and 703 panels will be used to create a RFZ. If I need to add more information for you to give input, please let me know. I appreciate all responses!

Hi "Bucky", and Welcome to the forum! :)

... electrical and HVAC are non-issues in this question.

I'm just a little curios about that: How can they be "non-issues"? All studios need both electrical and HVAC installations, without any doubt, and both of those can greatly affect the isolation if not planned carefully and built even more carefully. So I'm curious as to why you think they would not be an issue?

7.5' x 11.79' x 19.08' (HxWxL, giving me a ratio of 1:1.57:2.54)

Not such a good ratio: there are three dips on the Bonello diagram for that room, and it is not very near to any known good ratio. The closest good one I see at first glance would be around 1: 1.5 : 2.2, or 7.5' x 11.25' x 16.5'. Louden's 4th best ratio.

Assuming I orientate the mixing setup long-ways, is there a benefit to building new 10% splayed walls on each long side?

Possibly, but not necessarily. Assuming you do that to get the average width down to 11.25', and also chop three feet of the length (to make 16.5') then it might be a good idea. You don't need to splay the entire wall: just the first few feet, as far back as the mix position, probably.

In your opinion will there be a potential reduction in flutter echo in the ~1700 sq ft room?

I think you mean cubic feet, not square feet! :) But anyway, room volume is not really relevant to flutter echo (only indirectly). And the final volume for the ratio I outlined above, would be more like 1400 cubic feet: That's still fine for a critical listening room. Flutter echo is related to having parallel walls, so yes, from that point of view splaying your walls 10° on each side will help... but only for flutter between those two surfaces: it will do nothing for potential flutter echo in the vertical plane, nor in the front-back plane. It would only affect side-to-side plane. Besides, there are other ways of dealing with flutter echo. Splaying your walls is not the only solution, and flutter echo in the side-to-side plane might or might not even be a problem!

Also assume that the four vertical corners will be trapped,

That might or might not affect flutter echo. Depends on several factors.

and 703 panels will be used to create a RFZ.

I can't see how that would work. 703 is absorbent: you cannot create an RFZ with absorption. The surfaces need to be highly reflective for that. You do need thick absorption on the rear wall, yes, but the actual surfaces involved in creating the zone, must (by definition) be highly reflective. That's the concept of RFZ.

If I need to add more information for you to give input, please let me know.

Photos would help! :) It makes it easier to understand what it is you are dealing with if we can see it, so it would be good if you could post a couple of photos of the room as it is now. - Stuart -

Stuart, thank you for the outstanding replies to my questions. I appreciate the time you put into this.

... (electrical and HVAC) I'm just a little curios about that: How can they be "non-issues"?

I only say that because the room has existing electrical and HVAC, and none of the outlets (or registers/returns) will be in the way of the potential new splayed-walls. I didn't want anyone to think that I needed to build new soffit-mounted ducts or anything.

Not such a good ratio: there are three dips on the Bonello diagram for that room, and it is not very near to any known good ratio. The closest good one I see at first glance would be around 1: 1.5 : 2.2, or 7.5' x 11.25' x 16.5'. Louden's 4th best ratio

So either I shorten the length of the room approx 3.5', or Louden re-works his math. :) I believe I will shorten the room with an additional wall.

You don't need to splay the entire wall: just the first few feet, as far back as the mix position, probably.

Excellent. And when measuring a splayed room like you did, am I correct that you use the average width/length?

Besides, there are other ways of dealing with flutter echo. Splaying your walls is not the only solution, and flutter echo in the side-to-side plane might or might not even be a problem!

So Stuart, you are me, here in the midwest. Do you pay the contractor (who is very talented and cutting you a GREAT deal) to frame, sheetrock, and finish two new splayed walls that extend approx to the mix position? Or, do you look at the cash in you hand and think "Man, this could really upgrade some sweet gear!"? (Assume we will continue on with the room treatment options)

and 703 panels will be used to create a RFZ.

I can't see how that would work. 703 is absorbent: you cannot create an RFZ with absorption. The surfaces need to be highly reflective for that. You do need thick absorption on the rear wall, yes, but the actual surfaces involved in creating the zone, must (by definition) be highly reflective. That's the concept of RFZ.

I am dumbstruck by this. I completely misunderstood the concept behind building a reflection-free zone. Would you mind expounding on this or providing a favorite link or two so that I can understand the idea behind it?

Photos would help! :) It makes it easier to understand what it is you are dealing with if we can see it, so it would be good if you could post a couple of photos of the room as it is now.

Pic coming very shortly. Again, this is invaluable to me. Thank you very much. -Bucky

So Stuart, you are me, here in the midwest. Do you pay the contractor (who is very talented and cutting you a GREAT deal) to frame, sheetrock, and finish two new splayed walls that extend approx to the mix position? Or, do you look at the cash in you hand and think "Man, this could really upgrade some sweet gear!"? (Assume we will continue on with the room treatment options)

If it is just flutter echo that we are talking about, then no, I would not pay the contractor, and would not splay the walls. However! You mentioned RFZ, which is the REAL reason why you would want to splay them. So that leads us to ....

I am dumbstruck by this. I completely misunderstood the concept behind building a reflection-free zone. Would you mind expounding on this or providing a favorite link or two so that I can understand the idea behind it?

The concept is this: You angle the front section of the side walls enough so that the first reflections cannot get to your ears: Instead, they go to the rear wall where they are partially attenuated by the thick absorption back there. Those reflections will eventually get back to your ears, of course, but the philosophy is this. No reflection gets to your ears until at least 20 ms after the direct sound from the speakers already got there, and even then the level is at least 20 dB lower. That's the strictest measure, but hard to achieve. A more reasonable measure is to relax that to 15 ms late and 15 B down. For a small room, you might even have to go as low as 10 ms late and 10 dB down, but that's the limit. This is all about the way the brain perceives sound: if the same sound arrives at your ears twice within 20 ms and at roughly the same level, our brain can't figure out that it was actually two sounds, one being an "echo" of the other: instead, it sort of "smears" them together, blurrily (does that word even exist? :)). That messes up your ability to determine where the sound came from: It blows away your stereo image and sound stage. But if they arrive more than 20 ms apart, and with more the 20 dB difference, your brain figures that the second one is just a reverberant echo of the first, and all remains right with the universe: your brain can deal with directions much better, allowing you to perceive the sound stage clearly, and to accurately determine where each instrument is apparently coming from, between the speakers. So, in order to do all that, the first reflection points must remain hard and reflective, and must be angled enough to send those reflections well away form your ears, to the back wall, for absorption. It is not possible to have enough absorption to completely "suck up" the reflections at the first reflection points, and trying to use diffusers to break up the reflections is not a good thing (unless you are using a different design concept, such as ESS). So angled reflection is your only option, and that implies hard, flat, reflective surfaces, in order to get good clean specular reflections. Which leads to the obvious question: how much angle do you need to achieve that? And that's where things start getting complicated: there just isn't any simple answer to that. Nobody can say that "At exactly 12.856° of angle you always get a perfect RFZ. The answer is actually much more maddening: "It depends". Every room is different, and every room will have it's own minimum and optimum angles. The way you determine what that angle is for YOUR room, is with a technique called "ray tracing", which is time-consuming, and involves a lot of trial-and-error of projecting imaginary lines out from your speakers at various angles, seeing what they hit, calculating the "bounce" at that point, and following to see where it goes next. Unfortunately, unless you have a lot of money to spare on software analysis, that's the only real way to figure it out.

So either I shorten the length of the room approx 3.5', or Louden re-works his math.

:shock: :D Might be hard to convince him! :) There might be other ratios that would work: I just happened to find that one close by, more or less by accident. It may pay to fool around with calculators a bit, to see if something else comes up. HOWEVER! (And this is a big "however"). If you splay your walls enough to get a good RFZ, you have now very likely splayed them way to much to be able to use the usual simple room mode calculators! And Murphy yells out "Gotchaaaaaa!!!!", with a shriek of malicious glee and a sinister giggle... :) The problem is that room mode calculators only work accurately for perfectly rectangular rooms: The moment you splay any wall even a bit, the calculations are no longer accurate. Still useful, but not accurate. That said, as long as the splay angle is shallow, you can still use the average dimensions of the room to figure the rough modal response. But the greater the splay angle becomes, the less accurate the prediction becomes, until at some undefined point, the predictions are no longer useful.

Excellent. And when measuring a splayed room like you did, am I correct that you use the average width/length?

Yup! But only if the splay is not too severe. Where "too severe" is a concept that nobody seems to be able to define! So a 1° splay is "No problem", and a 45° splay is "Are you nuts?", while all the degrees in between are just a blurry range of mushy approximation... ( I guess that's not much use to you! :( ) - Stuart -

Stuart, I have carefully read and re-read all of the information that you diligently posted for me (and others) to learn from. One thought kept racing through my head; Maybe I will become a fireman. Or an astronaut. But I gotta get out of the music biz! :D Lets assume I stay. I'm now considering NOT adding splayed walls to the room. Instead, continue with the interior treatments, including floor-to-ceiling bass traps in all four corners, and additional trapping along the horizontal corners created by wall-to-ceiling junctions. Clouds will be hung from the (already very low 7.5') ceiling. And finally, I will research and build correct panels to hang on the parallel side walls that angle early reflections to the rear of the room. Speaking of room: (Edited to temporarily remove waaaay oversized picture) Thanks for any additional comments and help!!

This view of the room is taken from the doorway. The cinder block wall that we are facing measures approx 7.5'H x 11.9'W. The two walls on your left and right were the ones that I was considering splaying.

Looking at that photo, I think it's a good decision to not splay the walls: it looks like that would make the room too narrow, so you are probably better off with the parallel walls and treatment for possible flutter echo.

I will research and build correct panels to hang on the parallel side walls that angle early reflections to the rear of the room.

You are probably better just going with thick absorption on your first reflection points. Angling reflective panels might not work too well, as you don't have a lot of room width to play with, and you'd have to do it along the lines of the CID concept, not the RFZ concept. It would work, but might not be easy to achieve. The rest of your plan sounds great! That should work well. Make the bass traps as big as you can, and as deep as you can. You might also need to consider some of the other corners on the room for bass trapping, too (there are 12 corners in a rectangular room...) - Stuart -

... just following along in the control planning ... always educational for ALL of us [Thanks Stuart] ! In you first post, it's mentioned that 'isolation' is not an issue. Just to better understand, is the situation such that you don't need to elevate the level of isolation ? In other words, working at 'mix' levels will not be a nuisance to the 'surrounding' area or neighbors ?? If that is the case, from the photo, it looks like you already have the structure ready ... just supposing. Again, if you need no further isolation, then might you only need to install treatment [4 corner bass traps, broadband absorbers on all 4 walls, a mix of hard backed/ soft backed clouds for the ceiling] ?? Just trying to understand the design criteria and goals better! Sincerely.

RJHollins wrote:

In you first post, it's mentioned that 'isolation' is not an issue. Just to better understand, is the situation such that you don't need to elevate the level of isolation ? In other words, working at 'mix' levels will not be a nuisance to the 'surrounding' area or neighbors ??

That's correct. Working at mix levels will not disturb anyone. In the same complex is my live room, which is ridiculously isolated and tuned, thanks to this forum and The Soundproofing Company. (btw, I never ever want to see Green Glue again)

Soundman2020 wrote:

Looking at that photo, I think it's a good decision to not splay the walls: it looks like that would make the room too narrow, so you are probably better off with the parallel walls and treatment for possible flutter echo.

I will research and build correct panels to hang on the parallel side walls that angle early reflections to the rear of the room.

You are probably better just going with thick absorption on your first reflection points. Angling reflective panels might not work too well, as you don't have a lot of room width to play with, and you'd have to do it along the lines of the CID concept, not the RFZ concept. It would work, but might not be easy to achieve. The rest of your plan sounds great! That should work well. Make the bass traps as big as you can, and as deep as you can. You might also need to consider some of the other corners on the room for bass trapping, too (there are 12 corners in a rectangular room...) - Stuart -

Thanks again Stuart. I will go with

-thick absorption at the first reflection point

-2' wide bass traps from floor to ceiling in each corner

-triangle bass traps at the four trihedral ceiling corners

-bass traps of yet to be determined length spaced along the wall-to-ceiling junction

three clouds