tetrahedron, I did not know that this is the name for the shape!

I gotta be the one to ask, Michaelz: how is the gorgeous tetrahedron with the stick on the front of it related to the cube in the corner?

It's the same cabinet or the back chamber of the "horn". From out side as in the first picture it looks like a cube, but it's hiding the tetrahedron against the corner of the room. The stick is used as support when the box is placed in the corner, so that the box will not lean against the walls. The upper side of the box in the second and third pictures is the down side in the first picture.

And why does it lead Wayne to wonder about nailing a board across the front of it?

Wayne's idea will make the space between the inner side of this board and the cone of the driver the front chamber of the "horn". The whole idea of "corner horn" is from Wayne's thought that below 40HZ in a average room, the bass is produced by the room corner unless the horn size is no problem. I just liked to make the coupling to the corner tighter and to reduce the size of the box itself. I would think that any 12" or 15" drivers suitable for horn loading would work this way. Just run the specs through the ML Util and simulate the horn in HornResp. I even have a small VB program to calculate the "room corner" conical horn size for use in HornResp.