control room shape/dimensions

[noxix]

Hi all,

I don't know if I should post this in acoustics or design, but ...

I've been doing a bunch of research for the past few months on control room design and I have yet to find any real info on dimensioning a non-rectangular control room.

After checking out the SAE site and looking at the "standard layouts" as well as the John Sayers designs up for discussion, and the steven klein designs at http://www.soundcontrolroom.com/ there are very often designs based on a square which has 2 pentagons created in it.

Well, clearly a pentagon is not going to be easily predicted, since based on other threads I've read, there is no low cost software solution for predicting room modes for that shape, or any non-rectangular prism.

So I guess my question, to John and others is:

How do you guys go about designing rooms in those shapes? Are there dimenion ratio which you have found tend to work well, or do you simply skip mode prediction and treat the room after it is built?

[John Sayers]

Any shape is going to have modes but if you treat the whole room to lower the verb time the modes get absorbed along with everything else. The geometry you refer to is based around the monitors, not the modes.

cheers
john

[noxix]

Thanks for the info John,

I interpret that to mean, "b" don't stress the room dimensions, treat the room modes later.

I was trying to compare the odd shaped rooms to rectangular rooms in terms of determining good ratios of length/width/height for even mode distribution.

[John Sayers]

I interpret that to mean, "b" don't stress the room dimensions, treat the room modes later.

no - I'm saying the modes will get treated along with the other frequencies when you treat the room normally to reduce the reverb time.

cheers
john

[noxix]

Hmm, I'm not sure I understand.

I would like to though.

My understanding is, unless you have an anechoic environment, the spacing of room modes will be a big factor in determining the smoothness of the sound of the room.

So often people build rectangular rooms with dimensions which are in certain ratios (either using "golden" ratios or a room mode calculator) which have relatively evenly spaced room mode distribution.

My question is: when building these odd shaped rooms, how do you predict whether the room modes will be distributed in a decent way?

Or put another way: How do you pick the proportions and dimensions of these rooms? For ray tracing and ergonomic reasons exclusively, or are there ratio ideas you are taking in to account as well?

I think you are saying that treating the room with low frequency absorption to reduce reverb time will lessen the effects of the modes, which makes sense to me, but it seems that the spacing of the modes would still be a factor in the usability of the room.

I am just curious because I am drawn to these room shapes, and understand the many advantages, but am confused about how to discover good dimensions for them.

Thanks for bearing with me ...

[John Sayers]

Firstly - the geometry of the splayed walls etc is not because of modes but because of the speaker projection. (the modes will still exist but can't be calculated accurately as one can with a rectangle.) You need to take the verb time right down especially by trapping the rear wall and stopping the rear reflections. The modes are reduced in this process.

cheers
john

[noxix]

I don't know if I am remiss and should be moving this in to the acoustics forum,

but what I am asking isn't about the modes conceptually ... I know the splayed walls don't eliminate the modes, and exist to deal with higher frequency reflections and speaker dispersion in general.

I guess what I am asking is ... since it is more difficult to predict accurately the modal response of non-rectangular rooms, are there any pratical, real world guidelines or principles one should use when determining the ratios of such room dimenions?

Most specifically, in the case of the "corner control room" sae design, is there any particular approach one might use when figuring out the relative dimensions of each of the 5 sides in the depicted control room?

Or are you saying that modal distribution just isn't a key factor in determining the quality of the monitoring environment when the room is treated in the manner suggested elsewhere on this site? That once a sufficient amount of bass trapping has been installed, room modes aren't all they are made out to be ...

Or are you saying the methodology of choosing room dimensions for that situation go beyond the scope of a bulletin board?

Thanks for you patience, am just grinding along over here ...


-- N

[knightfly]

N, several people claim that modes are also important in non-parallel walled rooms - one way I've seen used to estimate the effects is to take the AVERAGE distance between two non-parallel walls as the number for modal calculations.

In the case of the corner control room, this room is small enough that the rear should be heavily absorbed to avoid early reflections and so it won't be as prominent in modal considerations - I would draw a line between the two widest points in the room, near the couch - bisect that line with another line connected to the rear center corner, divide by two, and add that to the distance from the front of the room to the first line. This will give you a close average distance for the longitudinal mode. Any sloped ceilings can be calculated the same way.

In the case of non-parallel walls, close is close enough because of the Reflection Free Zone and adequate absorption. As of yet I've not built this type of room, only studied everything I could find on it - I am planning to use this concept in my impending new studio however... Steve