sorry missed this question, The demo video of the alpha panel advertises a hybrid of diffusion and absorption, so not sure why a GIK rep would tell you that it is purely cosmetic. It is possible whoever you talked to was unclear on the specs of the alpha panels (or the one who made the demo video was).
Specs from GIK website state:
“Thin face plate has mathematical sequence of slots for spatial diffusion, but also allows low frequency waves to pass through to the fiberglass panel for low end absorption.”
What is unclear is whether those “slots for spatial diffusion” go deep enough into the fiberglass or if it is really just a thin plate? From the images it doesn’t look like they go deep (not sure) but they (GIK) would not/should not be advertising it as a spatial diffuser, if that is the case. This could be a marketing mixup.
If it really is a thin plate that just sits on top, then, there would be no diffusion going on but certain high frequencies could bounce off (reflect)…
In theory the Hybrid panels could indeed do “true spatial diffusion” and absorption together if they were designed like Case 1 (absorptive fiberglass cut into deep cavities with a reflective lining, see fig.)
We will need someone to physically see the depth of the Alpha panel slots and inspect the lining inside the slots.
I think this design analysis would make more sense (not made to scale, showing top cross section):
Only Case 1 is an ideal diffuser absorber hybrid, Case 2 is NOT.
If the Alpha panels are case 2 then the faceplate is pretty much cosmetic and serves little purpose. Reflections off a flat plate isn’t really ‘ideal’ scattering either, so It could potentially cause problems. Since, the alpha panel in that case would be technically just absorbing lows and reflecting frequencies in the range of 16khz+ directly back to the source (since the reflecting surface is not angled), it could create comb filtering if placed directly behind the speakers.
As for minimum room size and diffusion:
For diffusion to be effective, the listening position needs to be far enough away for diffusion to mature. The maturing distance depends on the wavelength of the lowest frequency diffused.
If in a true diffuser, let’s say the lowest frequency diffused is 565 hz (6 inch deep),
A matured diffusion for this frequency would form at multiples of 150% of wavelength, so the absolute minimum distance from ‘diffuser to listening position’ would need to be between 3 ft to 5ft. So you can see you don’t really need too much space for effective diffusion. Most spaces are larger than 5ft so that shouldn’t be a concern for most well made diffusers.