Q: Are there any phase or lobing issues with the Ramp diffuser? Can I place them side to side abutting each other in exactly the same orientation?
If there are lobing issues, how widely should they be spaced apart to minimize the problem?
A: All arrays of diffusers have some kind of lobing or artifacts, but the ramps are significantly better than box-style QRD diffusers. The resonant cavities on the ramps are less parallel and therefore are less tonally resonant.
I have found that you need your ears to be about 2-3 times the depth of the diffuser to avoid being able to notice the artifacts or lobing when you move your head back and forth when the Ramps are installed vertically.
In a control room, the best way to avoid the lobing issue is to do a set up like I did at Echo Boston (http://www.xix-acoustics.com/2012/07/19/acoustic-ramp-diffuser-install-at-echo-boston/
The artifacts are only audible when you move your ears up and down when you are very close to the ramps. This configuration is the best sounding of all of the installations for a control room’s rear wall because there is an extremely even diffusion both horizontally and vertically. The improvements in sweet spot imaging are really surprising.