Thanks for that information Sri, I think you mean between faceted and curved round back. As I understand it, an arc is always stronger than a flat surface, so you might be able to get away with 3/8" although that bending plywood sure looks limp. I would still always use 3/4" plywood bracing to help ensure a straight brace, it will be crucial to build these things square and true with NO racking or it will turn into a disaster quick.
I am hoping that the speaker front will be a nice veneer of wood and not just an ugly giant grill cloth stretched over everything.
We could make the detachable port board rectangular to match the horn, we just need some attractive seam cover to hide the joints. I suppose the entire front baffle could be detachable and could be attache to the speaker around the edges, but we would need to make sure nothing rattles at the sound decibels you will be able to achieve.
Since these speakers a designed to be rotatable, we should come up with a turntable for both linked together with belts and pulleys such that they will both always be in unison and aimed at the center of the room. Otherwise you will have to have permanent lasers installed to help with aiming.

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