Corner Control Room Ratios

Hi All, The known good ratios seem to apply to rectangular control room designs - how are they applied or calculated for a Corner control room suchas the one John has in the example layouts or the one in Rod's book? Is there a formula to take an odd shaped room and find the rectangular equivalent or something? Sean

Anyone? We all understand that ratios are most important when it comes specifically to Control Room as we strive for an acoustical neutral environment or at least one where we can control the acoustics relatively easily through treatment. The ratios themselves are represented down to the second decimal place so the idea is to work accurately. Therefore I don't think the rectangular shape that best lays over the top of the Corner Control Room is going to cut it. There must be more to it and I realize the maths involved is probably from another planet but we need to understand what is involved or at least attempt to. The ratios I would think not only take into account the linear side lengths but also the volume that results as all these will be sympathetic to some frequencies. So the Corner Control Room which is the other most prolific design after the rectanglular room will need to be defined properly if it is to be built to any scientific degree. I guess the real issue is defining the effect of angular wall displacement on resonant frequencies and how this is affected when the walls diverge or converge. In the normal Corner Control Room the walls diverge from the monitor position and converge at the rear. Let me know what your thoughts are. Sean

The ratios themselves are represented down to the second decimal place so the idea is to work accurately.

True, but there is no need to go overboard, either. At 20 kHz, a quarter wavelength is roughly 5 mm, so it is pointless to worry about precision much better than that! And at the other end of the scale (where big problems lie), at 20 Hz you are talking about quarter wavelengths of nearly 5 meters, and 200 Hz is half a meter! So approximating a slightly non-rectangular room to the closest rectangle is an acceptable idea. If your walls / ceiling are splayed by less than a meter, then it seems to me that you'll be in the ballpark up to about 200 Hz, if you fit a rectangle to the mid point of the splayed wall / ceiling, and use that for your ratio. And above 200 Hz the modes are so close anyway that it doesn't really matter any more. In any event, it seems that ratios are a merely a good starting point, but that carefully choosing speaker and mix positions is even more important, according to some folks. Of course, you can't compensate for a a 1:1:1 ratio just by choosing good speaker/listening positions, but you CAN screw up an excellent room ratio by lousy positioning of speakers / mix position, making it sound nearly as bad as a 1:1:1! Not to mention that even in the best-built rooms, actual measurements taken on the final untreated room, usually do NOT match the predictions with a large degree of accuracy: They are close, but not exact. Which I guess is why guys like Rod and Ethan always tell you to actually measure your room before treating it, and not to just rely on calculations alone. Now, if you really DO want to be precise down to the last millimeter at all frequencies for your grossly non-rectangular room, then forget trying to do the math with pencil and paper. No way. From what I've found out from a bit of research I did a while back, the only way to figure that out, is with finite element analysis software (FEA), using the technique of finite element modeling (FEM). Basically, what that means is that you use FEM/FEA software to represent your room as hundreds (or preferably thousands) of tiny imaginary "elements" (think of them as cubes) that are linked to each other in a lattice of springs and dampers, and the software figures out how waves travel through those "elements", then shows you the results in a 3D display. Which you then have to interpret! The pictures look pretty, but unless you understand what they mean and what to do about it, then its kind of a pointless exercise. In other words: "Don't try this at home, kids!" If you want that kind of analysis done right, then hire an acoustician who knows how to do it, and how to interpret the results. So, in summary, its "good-news, bad-news, good-news": The first good news is that you actually can figure out good dimensions for severely non-rectangular rooms. The bad news is that you probably can't do it yourself, unless you already understand FEM/FEA. (And you almost certainly cannot do it on the back of an envelope!). Then the final good news is that, for the size of rooms most of us are working on (or thinking about), a "best-fit" rectangle actually is a reasonable substitute, as long as you recognize that it will only be a rough approximation, and only good up to a few hundred Hz at best. My US$ 0.02. - Stuart -

Soundman2020 wrote:

Then the final good news is that, for the size of rooms most of us are working on (or thinking about), a "best-fit" rectangle actually is a reasonable substitute, as long as you recognize that it will only be a rough approximation, and only good up to a few hundred Hz at best. My US$ 0.02. - Stuart -

Can someone explain (perhaps with an image/example) of how this "best-fit" rectangle might fit over/around/inside a non-rectangular CR?

Hi Lydian. Do you have a thread for your studio here? If so, then why not post a rough design of what you have in mind, and I'll see if I can sketch in a rectangle that sort of fits. - Stuart -

Hi there. I am also seeking a ratio for a grossly non rectangular room. My thread is newbie needs help with unusual project in triangle rooms. Help pleeeeeaaaaseeeee!!! Donal

unusual project in triangle rooms.

I honestly would not have a clue how to calculate for a triangular room. You have no axial modes at all, I would imagine (except vertically), so only tangential and oblique would come into it. All the tables I've seen are for rooms that have basically four sides, even if there are additional surfaces involved at angles, but only three sides is something that I have not seen. I'd say that FEM/FEA is the only option, if you want to keep it triangular. Maybe a better option would be to build a normal rectangular (or nearly rectangular) room WITHIN that triangle. Use the triangle as the outer leaf, and build a normal shape inner-leaf. Then you can calculate your modes easily, using the normal methods. And you can use the strange shaped leftover bits from the triangle as storage space, or maybe as part of a booth or live room. That would be my suggestion. - Stuart -

Hey there, Unfortunately the room is just way way to small to build another room inside of. (roughly 5m x5m x 5m) However it does already have one corner of the room taken up with a booth already. This leaves me a space that is still roughly a triangle. When i look at most cr room plans here on the site, the splayed wall design i see is allready almost incorporated into my building. I am not quite 100% sure about the angles, but from what i read, if i place correctly (38% of room lenght??) and then angle my monitors 90 degrees i should have just about the right shaped room and reflection points. Is this thinking skewed??? There is an accurate skp of my room plan on my own thread "newbie needs help with unusual project in triangel rooms" If you could have a look at it your opinion would be greatly appreciated. Thanks df

It is a pain in the ass to apply FEM (I have done it previously) so my idea is if the room is already existent just jump into measurements in place