I have been quite busy lately. Slowly but surely the speakers have now been assembled and tested with various sounds, and they are behaving as expected. The picure shows the current status. First I used a sander with corn 60 to straighten out the joints. Then corn 120 and a layer of base paint. Then I repeat sanding and layers of high gloss white paint until the surface is all nice and uniform. As a finish I expect to apply two layers of laquer. I'm glad I didn't start a project like this: http://www.royaldevice.com/custom.htm (scroll down to the horn subwoofer!).