@arafiq I know GIK wanted to sell me the polyfusor’s behind them, but that was before they came out with the slatfusor’s or their own Q7 diffusor . I am curious to know what they would recommend now, but me being in Canada the cost of shipping was the same amount as the cost of the products, so I decided to make my own. I found some excellent acoustics resources I could share with you if you are interested, based on those I decided to go with a quadratic residue style. I wish I could give you the listening impressions of my N11 diffuser compared to an N13 or other, but that is the only one I have heard. So no idea if diffusion from 500 hz to 4200 hz is better than 680 hz to 5300 hz (going off the top of my head :) I chose the N11 because of the size. It was a fun project and yes, it does work, very well. I just have been thinking of adding more above them to the ceiling- because the speaker exceeds them in height they should diffuse in that area as well. (in theory)
If you have the budget for Dragon cables, If it were me, I would definitely get this diffusor: RD Acoustic I think it looks awesome, I may have one in the future. Does it sound better or worse then mine? No idea :)
My philosophy is diffusion on the front wall, absorption on the back wall. I do have some extras on the side walls, but I don't think they do much- maybe reduce a bit of slap echo. I don’t think a wee bit of foam on the front wall (behind the paining) will do anything to improve soundstage, but it may tame a little of the high frequencies if one feels that is necessary.
The common approach suggested in the planar forum was a few fig trees, I did that years ago also, and they did work for the highest frequencies to improve imaging, and the price was right, but these N11 quadratic diffusors work better.