Calculate the volume of an irregularly shaped room?

[Adze]

Hi all!

I'm fairly new to studio design. In fact I'm in my last year of college. As a project, I've been asked to design a hypothetical recording studio from scratch. I'll post my layout idea below. As you can see, I decided to make the side walls of the control room and the iso booth narrow slightly, with two of the corners rounded off, if you see what I mean. The problem is I have no idea how to calculate the volume to use for RT60 calculations.

To be honest, as I was typing this, I realised that I could probably calculate the volume of the whole rectangle, and then calculate the volume of the unused space and then subtract that from the rectangle. Is this correct?

The control room and iso booth are rooms-within-rooms, so essentially all white spaces are considered unused space.

Any help would be appreciated!
Adam

[Eric Best]

Hi all!



To be honest, as I was typing this, I realised that I could probably calculate the volume of the whole rectangle, and then calculate the volume of the unused space and then subtract that from the rectangle. Is this correct?


Adam

Exactly. Calculate the area of the rectangle then subtract the area of the two triangles.

[Soundman2020]

Hi. Please read the forum rules for posting (click here). You seem to be missing a couple of things!

I decided to make the side walls of the control room and the iso booth narrow slightly,

Why? It's a myth that you need to do that. A very, very wide-spread myth, true, but a myth, nevertheless.

The usual reasons put forward for doing that, are "To eliminate flutter echo" and "To get rid of the modes". However, in order to eliminate flutter echo, you would need an splay angle of at least 12° on your walls: anything less does not accomplish the task. And you cannot eliminate modes by angling walls! All you accomplish is to move some modes from one frequency to another, and to broaden the resonance peak. If you angle the wall steeply enough to actually get rid of an axial mode, then it would be replaced by one or more tangential modes, and one or more oblique modes....

Besides, it is also a fallacy that you should even try to "get rid" of modes. The problem in a small room is not that there are too many modes, but rather that there are not enough! That's the issue: too few modes available for too many notes on the musical scale. The goal should be to have as many modes as possible, spread around as evenly as possible.

In other words, there is zero reason to splay your walls.

with two of the corners rounded off,

Why? "Rounding off" the front corners of the room removes the very best location in the room for bass trapping! By eliminating those perfect, prime areas, you force the need for a much larger amount of bass trapping at other locations in the room, which takes up a lot of space. You also remove any possibility of "flush mounting" or "soffit mounting" your speakers, which is the best possible thing you can do for your speakers and for your room, to get the smoothest acoustic response. You need those corners for the "soffits" (flush mount modules). By eliminating those, you are forcing the room into a less than optimum configuration, where the speakers will have to go on stands, instead of being flush mounted. Speakers on stands will have major issues with SBIR, edge diffraction, power imbalance, phase cancellation, comb filtering, and several other artifacts.

The control room and iso booth are rooms-within-rooms, so essentially all white spaces are considered unused space.

It seems you are not correctly understanding the concept of "room in a room". You are showing EACH room as having two walls, but that is not how it works. Rather, your entire studio will have one wall around it, which is the "outer leaf" of every room, then each room is built as a single leaf, which is the inner-leaf for that room as well as being the outer-leaf for the other rooms.

Like this:

MSM-two-leaf-WallChunk-conventional--NOT-inside-out--one-room--S06.png

The above is how it would look for having just a single room done as a proper "room-in-a-room" system, such as maybe a control room in a basement.


Below is how it would look for three rooms done correctly. You can see that there is a single "shell" around the three rooms, consisting of just one "leaf" of mass, then each room is also done as a single leaf of mass. This might be the case for example in a series of isolated rehearsal rooms, where there is an access corridor next to them that is not isolated:

MSM-two-leaf-WallChunk-conventional--NOT-inside-out--three-rooms--S04.png

Thus, in both of the above cases (as well as any other arrangement of rooms, with any number of rooms) you will find that between any two adjacent rooms, there are only two leaves, and between any room and the outside world there are also only two leaves. This is the correct way to do a proper fully-decoupled two-leaf MSM isolation system. Also know as "room-in-a-room" construction.

The way you are showing it in your diagram, you have triple and quadruple leaves between rooms, which can potentially REDUCE your isolation, not increase it. Yes, you read that right: Having more than two leaves will give you LESS isolation than having just two leaves, all other factors being equal. You have a four-leaf window and a four-leaf door (which it would be impossible to open) between your control room and iso booth, as well as three leaf window between the control room and live room. You should only ever have two leaves between adjacent rooms. That implies that your windows will also be two-leaf, with one single pane of glass in each leaf. Your doors will also be doubled, with one single solid door in each leaf.

The problem is I have no idea how to calculate the volume to use for RT60 calculations.

If you model your studio in SketchUp, you can simply and easily read of the exact volume of a room that has any arbitrary shape, even with multiple walls at odd angles. The software calculates that for you.


- Stuart -

[Adze]

Thank you! This helps a lot, I'll absolutely go back to the drawing board and edit the room designs. I must have misinterpreted a bunch of stuff from my lectures - thanks for pointing out the flaws.

I should have mentioned that for the purposes of the project, only the axial modes need to be addressed, hence my attempts to work with them. I think what I was trying to do was lay out the control room in the classic coffin shape and got a bit muddled up. But I'll definitely take this and work with it Also, I absolutely see what is meant by rooms-within-rooms now!

I'm still fairly new to this all - diffusers would be best to get as wide a spread of the axial modes as possible, correct?

[Soundman2020]

I should have mentioned that for the purposes of the project, only the axial modes need to be addressed,

That's strange! Not a very good way of analyzing a room. If you only consider axials, then your Schroeder frequency is going to be waaaay up high, and you'd stand pretty much zero chance of getting a usable modal spread, unless the room is very, very large.

Here's the two cases for a hypothetical room measuring 7m x 6m x 2.4m:

Axials only:

H-room--only-axials.jpg

All modes:

H-room--all-modes.jpg

As you can see, there's not much chance you'd be able to adjust the dimensions to spread around the modes, if you only have axials to play with! Besides, it rather silly to even try, since rooms in the real world always have tangentials and obliques...

I think what I was trying to do was lay out the control room in the classic coffin shape and got a bit muddled up.

Nobody actually builds rooms like that. The shape itself is entirely misunderstood: It shows the final visible surfaces in the room, after treatment, not the actual shape of the room's boundary surfaces. And even then, it is deficient. I'm surprised that they are still teaching you that! I wonder if they are also teaching LEDE as being the best, most-used design concept? I sure hope not.... It was abandoned decades ago.

diffusers would be best to get as wide a spread of the axial modes as possible, correct?

Nope. Diffusers do not change the modal frequencies in any way. The modal frequencies are determined by one thing alone: the dimensions of the room. The modal spread is fixed for any given room, by the distances between the solid, rigid, hard, massive boundary surfaces of the room. The only way to change the modal spread, is by changing the dimensions.

Diffusers are also not much use in treating modes: Major modal issues are all in the low frequency end of the spectrum (below the Schroeder frequency, obviously), and diffusers just don't get down that low. At least, not the normal type of diffuser you commonly see in control rooms (skylines, QRD, PRD, BAD, etc.) Those are rarely tuned into the low end: more often they treat the mid range. In order to diffuse modal issues, you'd need huge diffusers, measuring feet long and each element would need to be many inches wide. Not usually practical.

Modes are usually damped with deep porous absorption, usually on the rear wall of the room, and in several other corners.

If you don't already have it, you might want to get a copy of Master Handbook of Acoustics, by F. Alton Everest. Very much worth the read.

And of course, feel free to browse all over the forum, to see how real studios are designed and built in the real world, rather than theoretically in the classroom! We have over 21,000 members here on the forum, and hundreds of studio builds. Here's an interesting one, that shows you what can be achieved in a good modern control room, when everything is done right: http://www.johnlsayers.com/phpBB2/viewt ... =2&t=20471

- Stuart -

[Adze]

Thanks again! I agree, focusing on axials only is a weird way of doing it. I guess the logic is that I'm doing a Sound Engineering course and they're only planning on teaching us the bare fundamentals of studio design. In fact this is our only acoustics project for the entire course. I hate to make excuses but I'm pretty much as green as it gets when it comes to this stuff, so at least I'm not completely at fault for the time being.

And god, Amroc is an absolute god-send. I've since completely rewritten my floor plan and made the room ratios sit right (except the live room. Still working on that.)

I'll absolutely check out the thread you mentioned too, that should make everything much easier.

Thanks Stuart, this is really helping a lot!