Hi there Peter, and welcome!
I wonder if I can change the orientation of the room dimensions? Would a room (in meters) of 3.0x3.84x4.62 (HxWxL) sound the same as 3.84x3.0x4.62 (HxWxL) or even 4.62x3.0x3.84 (HxWxL)?
I assume that we are talking about your control room here? Room ratios are a lot less important for live rooms than for control rooms, so I'll assume your question is about the CR.
Room ratios are all about the modal response of the room: The frequencies at which there will be natural resonances (reverberation) of the room, simply due to the distances between the surfaces. Good ratios merely mean that the modes are spread out smoothly across the low end of the spectrum, rather than being bunched up in one place with big gaps between them.
So from that point of view, it does not matter which way you orient the room: the modal response of all rooms that have the same dimensions will always be the same: You could even have it 4.62 high x 3.84 "wide" and 3.0 "long" if you wanted, and the modal response would be the same.
However, that does not mean that three identical rooms oriented in different manners would SOUND the same: That's a different thing. The sound of a room depends on many more factors than just the modal response. What you perceive in the room depends on things like the relative locations of the sound sources (speakers) and receivers (your ears), in relation to the surfaces of the room. If either the speakers or your ears are close to one of the room surfaces, you will perceive reflections, phase cancellations, comb filtering, bass build-up, SBIR, and other artifacts. The greater the distance, and the larger the angles, the less effect you hear. So, for example, if you orient a room to be very wide but not very long, then you would have large reflections coming from the rear wall, but not from the side walls (or earlier from the rear than form the sides), but if you oriented it so that it is narrow but long, then the reflections form the side walls would arrive
before the reflections form the rear wall: it would sound different.
There are also other issues in play here, such as the Haas time: That has to do with psycho-acoustics (the way your ears and brain interpret sounds), rather than the room itself. Basically, if your ears hear a sound and the reflection (echo) of the same sound within less than 20ms of each other, then your brain cannot figure out that the second one is a different sound: it perceives them as one single sound, smeared out over time, with a different frequency response, and coming from a different direction than it really came from. But if the echo came more than 20ms after the direct, then that's enough for your brain to identify that this really is an echo, a separate repetition of the same sound, so it correctly interprets the frequency response and the direction of both sounds.
This is the reason why we recommend that the "diffuse field" or "reverberant field" in a room, which is mostly sound that bounced off the rear walls and came back to your ears, should arrive at least 20ms after the direct sound, and should be attenuated by at least 20 dB by the time it reaches your ears That's one of the basic principles of designing a top quality studio, or any other room that is meant for critical listening.
To do that, you need to have the rear wall at least 3m behind your head, no matter what the dimensions of the room are. If you can get the rear wall further back, then that's even better: over 4m is great, as that leaves you room to do diffusion with thick bass trapping behind it, on the rear wall.
If you can't get a distance of at least 3m between your head and the back wall, there are other techniques for helping to deal with that, but it is still preferable to have the room oriented as long as possible.
In your case, you are fine: a length of 4.62m is good: it allows you to set up the mix position with the correct geometry, and still have about 3m behind your head, to the rear wall. If you could make it longer, that would be even better, but you should be OK like that.
OK, but your question was more about the other two dimensions: Can you swap width for height? Here too, the answer is similar: You can, from the point of view of modal response, but it would not sound the same. Having a wide room gives you more flexibility with placing and orienting speakers, as the first reflection points are further away, the reflections take a longer path, and can be treated more suitably, as you have space for deeper treatment, and larger angles.
Yes, it is nice to have a high ceiling if you can get it, and certainly for something like a drum booth I would choose height over width if I had the choice, but for a control room, I think I'd prefer width over height, provided that the ceiling is still at a reasonable height. In your case, it is: a 3m inner-leaf ceiling is still pretty good. So I would orient your room at 4.6m long, 3.8 wide, and 3.0 high. If you could make it a bit longer, that would be even better.
A lot also depends on your basic design philosophy: if you are going to use something like RFZ, NER, CID, or something like that as the basis for your design, then it helps to start with a room that is even longer if you can, to allow for the angled surfaces and soffits at the front. But if you wanted a purely rectangular design, then it helps to get all the dimensions as large as possible, so you can have the speakers far enough away form the walls so as not to have phase cancellation artifacts in the low end of the spectrum.
So it's not just the overall dimensions: it's how you use them, and how you orient the room, and how you treat it.
2. If I pick a rectangular room size with good acoustic properties, would it help if I made it not exactly rectangular by putting walls slighly off-axis? Or can this make things worse?
Symmetry is critical to a good control room. The left half of the room must be a mirror-image of the right half. At least, the front of the room needs to be symmetrical: behind your head there can be some non-symmetry, but even then symmetrical is preferred.
So you cold splay both side walls by the same amount if you wanted, but the question is: why? For what reason do you want to do that? Once again, that depends on your basic design philosophy. For RFZ and CID, you have no choice: parts of the side walls MUST be angled in order to achieve the shape needed for those philosophies. But that only applies to the parts in front of the mix position: here too, the parts behind could be angled if you want, but do not have to be angled according to the philosophy. So in this case, the same question arises: Why would you splay (angle) the rear part of the side walls? It wastes space, makes construction more complicated and slower (and more expensive), and does not provide any real benefits that you could not get in other ways.
Under some circumstance, there
might be good reasons to angle the rear part of the side walls, such as to fit in with other rooms, are limitations of the surrounding building, but in general there is no need to to that, as it just complicates things. Keep them straight, even if you do go with an RFZ-style design (which is highly recommended: RFZ with soffited speakers is about the best you can possibly get for a control room).
- Stuart -