Trevor,
Really like the folded QRD designs. Think I might try a building a folded design using foam/board the way you did. Just have to figure out how to stiffen and support the fold … probably a combo of ply/foam held by standoffs. If I put the screen out 8” I can apparently get some effectiveness down to 125Hz … not sure how he’s calculating that … as he gives a theoretical number of 250Hz.

On the speaker blocking … I’d like to have some space between the screen and the front of the speaker … so no blocking behind. Just need enough space around it.