I made some wood diffusers without "walls" using a YouTube video as a guide. I used a 1/2 inch back panel and just glued all the boards together using 1x3's for the slats and 1x4's for the frame.
Diffusers
I'm currently constructing a modified QRD-13. I have made the depth 20", for more effective low frequency response. I'm considering making two QRD-11's to place in back of my listening chair. A while back, I saw a Utube video of a guy that made some "finless" or walless diffusers. Has anyone seen of heard of these diffusers? I have tried to find the video, but have been unsuccessful. I have absorbtion panels and thought if I placed the finless diffusers in front of them, it would let the sound be diffused, as well as absorb some of the low frequency.