Back wall...diffusion or absorption?

[Seeker of Rock]

Most of you are familiar with my little project by now, but for those who aren't here's a recap:

**I have one room for tracking and mixing
**Stand-alone building of concrete block structural walls, wood rafter roof with Hushboard and a sheetwood finish, decoupled 5/8" gypsum interior walls, decoupled concrete floor slab on grade, pitched ceiling
**Interior dimensions are 12'x13'-6"
**Behind the mix position (area I am facing) I have a 4'x6' area of Auralex 'Metro' series 2" foam
**Corners behind the mix position (area I am facing) I have (2) MiniTraps bass traps in either corner about halfway up the height of the corner with (2) more planned for the corners on the rear wall
**Every 2' on center I have a 2' wide 'stripe' of Auralex 2" wall to ceiling

For talking volumes and singing volumes (all I have done until I finish moving everything in and hooking everything up) the previous echoes (pre-acoustical treatment) are no more....it sounds 'controlled' at this point, not really any echo anymore even when I face the untreated back wall and sing. Given this info, any preliminary advice of whether I would be better off putting some absorption at the back wall or diffusion (I'll be purchasing two more traps for the corners, but am curious about the rear wall surface)?

 

[tmix]

I believe that unless you are 8 to 10 foot away from the back wall diffusion may not help you. Diffusion needs some space for the scattered image to not sound like hotspots.
Absorbtion would probably be better. I know you run the risk of too dead a sound (perhaps) but I remember reading that small rooms often are not good candidates for diffusors. ( I could be wrong)

 

[Seeker of Rock]

So absorption is the way to go on the back wall. In the 12' width of the back wall (remember I have a pitched ceiling that peaks in the middle of the wall) and with one RealTraps MiniTrap at either corner, any suggestions for the middle as far as pattern? Should I build the rear absorbers at the standard 2'x4' insulation dimensions, or cut the 703 into 2' squares and checkerboard across the wall? Probably quite a few possibilities here. What would LOOK cool, imo, would be to cut the rigid fiberglass lengthwise into 1x4' pieces framed out and then have a series of those every 12" o.c. or so across the back wall.

Any suggestions are appreciated. but if it is 6 of this/half dozen of that, and it doesn't really matter as long as there is a good amount of absorption on the wall, then I'm going to have a little fun with the dimensions and shapes, maybe.

 

[ofajen]

Given this info, any preliminary advice of whether I would be better off putting some absorption at the back wall or diffusion (I'll be purchasing two more traps for the corners, but am curious about the rear wall surface)?

You want to stop reflections that come within about 20 ms. So, the rule of thumb is you must have 10 feet behind you at least before diffusion alone is best. Your space is too small for that. If you can afford it, put Studio Traps behind the mix position a few feet, with the dead side facing the mix position (the back of your head). That will kill off most of the first order early reflections off the back wall without giving any direct reflections from the traps themselves. The live sides facing the back wall will give diffuse reflections back toward the back wall and produce a bit of later in time diffuse reflection that reaches your ears by longer re-reflected paths.

Cheers,

Otto