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PostPosted: Mon Feb 19, 2018 5:21 pm 
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I have a long rectangular room 12m X 5m which I want to use as a hybrid control/live room and I see that almost all studio designs here have splayed walls. I understand that the splayed walls also serve as isolation from the outside concrete structure but in my case I don't need to have isolation so my question is if I should bother with splayed walls or just use absorptive treatments on the interior to help with flutter echo and standing waves etc? Are there serious acoustic advantages when using splayed walls over using acoustic treatment and leaving the room rectangular in shape?

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PostPosted: Mon Feb 19, 2018 11:04 pm 
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I understand that the splayed walls also serve as isolation from the outside concrete structure
Actually, that's not the reason for splaying walls, and splayed walls don't do much at all to improve isolation.

There are only really three reasons why people splay the walls of their rooms:

1) To eliminate "flutter echo", which is a type of resonance that can happen between parallel walls. But it's easy to deal with flutter echo in other ways, and the angle of the splay needs to be at least 12°, which takes up lots of space, so this is not a good reason.

2) Because it looks cool! They saw it in a photo, and liked the look, so they wanted to copy it but without understanding it at all.

3) If the design concept needs it. For example, with the RFZ design concept (many rooms here on the forum use this concept), you do have to angle certain surfaces at the front of the room such that the first reflections of the sound from the speakers (where it bounces of the walls and ceiling) do NOT go to the mix position. Rather, the angles are carefully chosen to send all of the early reflections to the back of the room, bypassing the mix position. And at the back of the room, those reflections are both absorbed and diffused, such that they arrive back at the mix position in the form of a low level ambient diffuses reverberant field. The same is true of the CID design concept, and the NER design concept, among others. If you build your room to one of these concepts, then yes, it is valid and necessary to splay the surfaces at the front of the room. In this case, it must be done carefully and accurately.

But it does not affect isolation.


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PostPosted: Mon Feb 19, 2018 11:14 pm 
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Soundman2020 wrote:
Quote:
I understand that the splayed walls also serve as isolation from the outside concrete structure
Actually, that's not the reason for splaying walls, and splayed walls don't do much at all to improve isolation.

There are only really three reasons why people splay the walls of their rooms:

1) To eliminate "flutter echo", which is a type of resonance that can happen between parallel walls. But it's easy to deal with flutter echo in other ways, and the angle of the splay needs to be at least 12°, which takes up lots of space, so this is not a good reason.

2) Because it looks cool! They saw it in a photo, and liked the look, so they wanted to copy it but without understanding it at all.

3) If the design concept needs it. For example, with the RFZ design concept (many rooms here on the forum use this concept), you do have to angle certain surfaces at the front of the room such that the first reflections of the sound from the speakers (where it bounces of the walls and ceiling) do NOT go to the mix position. Rather, the angles are carefully chosen to send all of the early reflections to the back of the room, bypassing the mix position. And at the back of the room, those reflections are both absorbed and diffused, such that they arrive back at the mix position in the form of a low level ambient diffuses reverberant field. The same is true of the CID design concept, and the NER design concept, among others. If you build your room to one of these concepts, then yes, it is valid and necessary to splay the surfaces at the front of the room. In this case, it must be done carefully and accurately.

But it does not affect isolation.


- Stuart -


I do understand what you mean but the splayed wall does affect the isolation because it is built as another layer within a room. In my case, I have a rectangle room that is long @ 12meters and only 5 meters wide. Now for me to splay walls in there would mean that I would build inner walls at an angles creating another layer of isolation would it not?

Then regarding number 3 in your reply. I kind of got the idea that this is why the walls were splayed in control rooms but I still am confused about one thing: How will splaying walls compare to using absorption at my first reflection points? For example, I could use an absorptive cloud over my head and use thick absorbers on the side walls or even use slats over the absorptive panels so as not to kill the high end. There seems to be an overwhelming preference here on this forum for splaying walls and I am really considering it BUT my control room is too long for it UNLESS I rotate my setup 90 degrees but then my control room will only be 5 meters long :(


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PostPosted: Tue Feb 20, 2018 12:39 am 
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I do understand what you mean but the splayed wall does affect the isolation because it is built as another layer within a room.
No it isn't! :) It is part of the inner leaf. If you build an additional wall within the room inner-leaf as a splayed wall, then you have create a three-leaf system, which will REDUCE isolation, not improve it.

Quote:
In my case, I have a rectangle room that is long @ 12meters and only 5 meters wide. Now for me to splay walls in there would mean that I would build inner walls at an angles creating another layer of isolation would it not?
You seem to be confusing splayed WALLS with angled SURFACES. It's not the same thing. If your inner-leaf is already built, as you say, then it is too late to splay the walls: they are already there! The only option left is to angle surfaces at the front of the room, such for example by building speaker "soffits" with angled front baffles, and angled "wings" out to the sides. But those are not walls: they are not sealed to the ceiling and floor, nor to the other walls around them. This is the best way to build an RFZ room. Splaying the entire wall is NOT necessary, and is a waste of space.

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How will splaying walls compare to using absorption at my first reflection points?
Splaying walls (or more correctly, angling surfaces in general) does not compare to putting absorption at the first reflection points, because it is far, far better! And a totally different design concept. Porous absorption at the first reflection points will PARTIALLY absorb SOME of the reflections... and that energy is then gone from the room. It no longer exits as acoustic energy, since it has been converted into heat energy. With reflective surfaces ALL of the energy stays in the room, and is then sent to the rear wall, where it is usually diffused and partly absorbed. So the energy is NOT removed from the reflection: it is bounced off at a different angle, to become part of the reverberant field. Absorption in the first reflection points does no absorb all frequencies evenly: it absorbs some more than others, mostly highs, but the mids and lows to a lesser and lesser extent, so it "colors" the sound. The absorption at the back of the room is specifically designed to deal with the low frequency issues, WITHOUT touching the highs.

Here's an example of how a control room is tuned, showing how this works in practice: viewtopic.php?f=2&t=21368

Quote:
I could use an absorptive cloud over my head and use thick absorbers on the side walls or even use slats over the absorptive panels so as not to kill the high end.
You might be able to get 4" of absorption in like that, but that's way to little to do what you would need. As you can see in the above thread, the rear wall uses a total of nearly 4 FEET of absorption and other treatment. You cannot do much with just 4".

In simple terms: it is not possible to create an RFZ room using porous absorption at the first reflection points.

Quote:
There seems to be an overwhelming preference here on this forum for splaying walls
Right: Because the RFZ design concept is simply the best one out there right now! If you want a room that has the best possible acoustic response, then RFZ is the first choice. There's nothing better. Here's a room that I designed using the RFZ concept as much as possible, and you can see the results: viewtopic.php?f=2&t=20471

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I am really considering it BUT my control room is too long for it UNLESS I rotate my setup 90 degrees but then my control room will only be 5 meters long
Why do you think your room is too long? It's a nice large room, and would work VERY well if you designed and built it as RFZ. 60m2 is the upper limit for a control room, and you are at it, but large rooms like that can have amazing acoustics. There is no need at all to rotate your orientation: The best way to do that room would be "lengthwise", with the speakers firing down the long axis.

Because of the size of that room, you'd need some careful design to produce the full RFZ effect. Part of the spec requires that the diret sound from the speakers hits your ears, then there are NO reflections or reverberations of that sound until at least 20ms later, and then when it does arrive, it is about -20 dB down, then decays slowly at the correct rate for the room size. That 20ms space with no reflections or reverberant field is called the "ITDG" for "Initial Time Delay Gap", and there does need to be a diffuse field that follows it, to give a sense of "ambiance" and "openness" and "iar" to the room. With a back wall 12m away, the there-and-back trip from the speakers to the rear wall to your head will be much more than 20ms (probably around 50 ms), so you will need to deal with that, and provide some earlier diffuse reflections to terminate the ITDG correctly.

But that's a really nice sized room! It could be world-class, if you wanted it to be. Does it have a high ceiling as well?

- Stuart -

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PostPosted: Tue Feb 20, 2018 6:21 pm 
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Hi Stuart

Thanks for all this info and I now understand the terminology better regarding splayed and angled wall :)

Regarding the distance to the back wall, a lot of designs I have seen have absorbent back walls with very thick low density treatments so could this be an option? If not then wouldn't using the 38% rule from the front of the room be an option? This would give a shorter distance for the sound to come back off the back wall.

Regarding the 1st reflection points, I was thinking more like 15" @ 7000 Pa.s/m2 for a 1st reflection point and was trying to compare this to the RFZ designs that are so popular on this site. I know 4" will not absorb the low end.

To answer your question, the ceiling height I have is 3 meters. It is not the best but I was thinking of having the ceiling absorptive. With the current height I could have around 50cm/20" to work with which would give me adequate absorption down to around 80Hz and average absorption below that. What do you think about this?

Vives en Chile? I have been several times because I used to live in Argentina and went travelling there a few times. I LOVE the northern part especially.


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PostPosted: Fri Jun 15, 2018 12:42 pm 
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regarding the distance to the back wall, a lot of designs I have seen have absorbent back walls with very thick low density treatments so could this be an option?
Yes, the back end of the room does need very thick bass trapping. That's pretty much always the case. I often use up 50cm or more of the room length for that. In the case of Franks' room, it is nearly a meter deep in the middle....

Quote:
If not then wouldn't using the 38% rule from the front of the room be an option? This would give a shorter distance for the sound to come back off the back wall.
You want a LONGER distance, not a shorter distance! You want at least 20ms after the direct sound hits your ears, and 30ms is better. So you want a decent long distance between your head and the rear wall, to allow plenty of time for that. 30 ms implies 15 feet from head to rear reflective surfaces.

Quote:
Regarding the 1st reflection points, I was thinking more like 15" @ 7000 Pa.s/m2 for a 1st reflection point and was trying to compare this to the RFZ designs that are so popular on this site
15" would be rather large! And would have a substantial effect on your overall room acoustics. Probably not what you want. With an RFZ design, you do NOT want to kill the room, acoustically. Removing huge amounts of energy at the first reflection points means that you will have no diffuse field at all, or that it will be way too low in intensity to be useful. The room will sounds dull, lifeless, and won't meet the BS.1116-3 specs.

A simple reflective panel will do the job much better, and keep all o the energy in the room, going the right way.

Quote:
To answer your question, the ceiling height I have is 3 meters. It is not the best but I was thinking of having the ceiling absorptive. With the current height I could have around 50cm/20" to work with which would give me adequate absorption down to around 80Hz and average absorption below that. What do you think about this?
Yes, you will need some treatment on the ceiling, but no, covering it all with 20" of absorption is not the right way to go about it! Once again, that would remove ALL of the energy that would otherwise be reflected to the rear of the room, so there would be no diffuse field at all. You absolute do need that diffuse field, and it should be arriving back at your ears about 20-30ms after the direct sound, and at a level of about -20dB, then it should decay slowly, at the correct rate for the room volume. It should decay even across the entire spectrum with no frequency band decaying faster or slower than 0.05s than it's neighbors on either side.

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Vives en Chile?
Claro que si! :)

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I have been several times because I used to live in Argentina and went travelling there a few times.
Cool!

Quote:
I LOVE the northern part especially.
Me too! A lot of people prefer the south, with the volcanoes, glaciers, lakes, and fast rivers, and I like that area too, but the north of Chile has a special kind of rugged beauty. Very dry, but still fascinating. Iquique is one of my favorites. And the beaches up there are much better than in the central region, where I live! The water up north is actually warm enough to swim in...

- Stuart -

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