I can't help with that particular design, but if you're willing to consider a different design, this one of mine works very well, and is almost trivial to construct -
http://www.diyaudio.com/forums/everything-else/269366-making-easy-diy-depot-sound-diffuser-panels-step-step.html
http://www.diyaudio.com/forums/everything-else/269366-making-easy-diy-depot-sound-diffuser-panels-step-step.html