Help deciding between 3 control room dimensions

[2k4s]

I'm building a room within a room to be used as a control room for composing and producing electronic and pop music and sometimes recording (in the control room) vocals and guitar in and I am able to choose the length of the walls somewhat.

I have settled in and around around 11'Wx17'Lx8'H

I can't raise the ceiling height without doing a sloped ceiling. i could get an average of 10' but it would be a 3/12 slope.
I don't want to go shorter than 11' on the width because of logistics. I could move it up to 12' or 12'6" at the most but 12' wall and 8' ceiling don't seem to like each other and i like 11' better then 12'6".
The length is where I have the most wiggle room. I really don't want to go shorter than 15' for logistical purposes but i could go as long as 18'

Using the calculator at http://amroc.andymel.eu/ , 11'Wx17'Lx8'H seems to be just within the bolt area and there aren't any axial modes stacked up on top of each other.

if i move the length down to 15' it looks pretty good. 150 - 153 hz looks to be a bit of an issue . maybe 120kz will need something. 15' is just starting to get a little cramped for me but i would do it if it was the best sound.

16' seems to have quite a few stacked modes of all types (i'm assuming because it is twice the ceiling height) so i'[m ruling that out. But I don't even know if I'm reading this right tbh.

I think I like 17' or 18' though because even though they are on the edge of the bolt area (not sure if that even matters as long as they are inside) they don't seem to have too many objectionable modes adding up on top of each other. I know i can also move back and forth inches and it will make a difference too but I don't even know if i'm looking at the numbers right before I start playing around with inches.

My question is, what room dimension would you recommend somewhere in between 11'x15'x8' and 11'x18'x8'?. or can you give me a little bit of information so that I can play with the numbers myself and be confident in what I'm doing?

[Soundman2020]

I can't raise the ceiling height without doing a sloped ceiling. i could get an average of 10' but it would be a 3/12 slope.

Which way would it slope? It it slopes upwards to the back (in other words, lower over the speakers, higher over the client couch), then that would be a good thing! But if it slopes side-to-side, then that's out.

but 12' wall and 8' ceiling don't seem to like each other

Yup! That's a problem. No dimension should have a direct mathematical relationship with any another, nor should it be within 5% of that.

The length is where I have the most wiggle room. I really don't want to go shorter than 15' for logistical purposes but i could go as long as 18'

In general, it is better to ahve a bigger room with more volume inside it, and it is better to have a longer room, to keep the initial reflections from the rear wall delayed by at least 20 ms. So if you can, then longer is better. Provided that it does not also create a really bad modal situation.

Using the calculator at http://amroc.andymel.eu/ , 11'Wx17'Lx8'H seems to be just within the bolt area and there aren't any axial modes stacked up on top of each other.

Try 17'11", 11'5", 8'. And use this calculator : http://www.bobgolds.com/Mode/RoomModes.htm

That ratio is very close to Louden's 4th best, you get 205 ft2 of floor area, which is pretty much the lower edge of what you need for a high quality control room, your modal spread is quite smooth, it's well inside the Bolt area, and the sun is shining brightly....

if i move the length down to 15' it looks pretty good. 150 - 153 hz looks to be a bit of an issue . maybe 120kz will need something.

It's a small room: it will need massive bass trapping anyway, so there's no point in worrying about treating individual modes, especially if they are up at 150 Hz, which is well above your Schroeder frequency anyway.

I think I like 17' or 18' though because even though they are on the edge of the bolt area (not sure if that even matters as long as they are inside) they don't seem to have too many objectionable modes adding up on top of each other. I know i can also move back and forth inches and it will make a difference too but I don't even know if i'm looking at the numbers right before I start playing around with inches.

Inches are important! But there's no need to go too crazy over modes: All rooms have them, there is nothing you can do to get rid of them (despite some ignorant beliefs to the contrary!), so you just have to live with them. The best you can do is make the room as large as possible in all three dimensions, then spread the modes around as evenly as possible in the low end, and that's it.

- Stuart -

[2k4s]

Which way would it slope?

It would actually slope from 8" high at the monitor side to 12' high at about 12' back and then down again for 4 or 5 feet, ending up at about 10' at the back. depending on how long the room is.
the gable. would this be bad? it would add complexity to the build, but the higher ceiling is aesthetically pleasing, otherwise i would definitely stick with 8' flat.

Screen Shot 2017-03-31 at 7.32.46 AM.png

17'11", 11'5", 8'.

i'll try this thanks!

Inches are important! But there's no need to go too crazy over modes: All rooms have them, there is nothing you can do to get rid of them (despite some ignorant beliefs to the contrary!), so you just have to live with them. The best you can do is make the room as large as possible in all three dimensions, then spread the modes around as evenly as possible in the low end, and that's it.

this is really good info that should be stickied somewhere. thank you!

[Soundman2020]

It would actually slope from 8" high at the monitor side to 12' high at about 12' back and then down again for 4 or 5 feet, ending up at about 10' at the back. depending on how long the room is. ... would this be bad? it would add complexity to the build, but the higher ceiling is aesthetically pleasing

Actually, I think that could work! Not only is it aesthetically pleasing, it can be acoustically beneficial as well. I think it's a real option. You might need to adjust the location of the peak and the slope angles, to avoid nasty reflections going to the wrong places at the back of the room, but the advantages are there, for sure.

By doing that, you help with the modal behavior in ways that are a bit hard to explain, you also eliminate flutter echo in the vertical axis, and you redirect the early reflections in the ceiling away from the mix position, as well as increasing the total air volume of the room... lots of good stuff.

The modal part is this: Those calculators only work for rectangular rooms with 6 sides, and considering that by dividing the ceiling into to planes at different angles you now have 7 sides to the room, the calculators won't work for your room any more. Or rather, they will still work perfectly well for some modes (the ones that do not involve the ceiling), will work less accurately other modes, and very inaccurately for yet others. But that's fine: They still work well enough to get an idea of how the room will behave.

So what will happen to the modes that can't be predicted simply any more? The ones that do involve the ceiling? Well, the don't go away! They are still there. But the move to different frequencies, they get sort of "blurred" a bit (lower Q), meaning that they are not so sharply defined any more, covering a broader range of frequencies than for a flat ceiling, and at a lower level. That's good!

I think this can work to your advantage, if you play around with those angles to optimize them.


- Stuart -

[2k4s]

Thank you Stuart.

You might need to adjust the location of the peak and the slope angles, to avoid nasty reflections going to the wrong places at the back of the room

I would have no idea where to begin with this. not even where to start reading. It seems very important to get right too. Is this type of ceiling over my head? (pun sort of intended).

the calculators won't work for your room any more. Or rather, they will still work perfectly well for some modes (the ones that do not involve the ceiling), will work less accurately other modes, and very inaccurately for yet others. But that's fine: They still work well enough to get an idea of how the room will behave.

I wouldn't know what dimensions to use for these calculators even to get a rough ides with the sloped ceiling. My assumption would be that I use an average of ceiling heigh and pretend it's a 6 sided room? Therefore, in effectively raising the ceiling height, I would need to adjust the wall dimensions to still try and get some good dimensions?

I hope you don't mind if I sum up what you wrote just to make sure i'm following correctly. The results of the calculator will not be accurate? But the benefits of the angles, the increased Q of some modes and the increased volume may outweigh any sub-optimal modal stuff that I might encounter due to not being able to accurately predict the modal behavior?

[Soundman2020]

I wouldn't know what dimensions to use for these calculators even to get a rough ides with the sloped ceiling. My assumption would be that I use an average of ceiling heigh and pretend it's a 6 sided room? Therefore, in effectively raising the ceiling height, I would need to adjust the wall dimensions to still try and get some good dimensions?

That's roughly right, yes, but also do calculations assuming that the entire ceiling is flat at the height of the lowest point, and another one assuming that the entire ceiling is flat at the height of the highest point. That gives you three sets of calculations that pretty much covers the range of possible moda distribution. It won't be accurate, but it will give you an idea of how things will work out.

The results of the calculator will not be accurate? But the benefits of the angles, the increased Q of some modes and the increased volume may outweigh any sub-optimal modal stuff that I might encounter due to not being able to accurately predict the modal behavior?

- Stuart -