How do you feel about different waveguide materials? In which ways does it matter?
Matarials can be varied, but the criteria is pretty well determined. The waveguide itself must not have any resonances in it at all. This is NOT the norm by any means. The standard method of mounting does not lend itself to good designs because the greatest mass is right where the cross section is minimum. The situation should be the exact opposite. The material cross section at the junction of the throat to the driver should be the greatest of anywhere along its length and this should be several inches. This means that injection molded plastic or fiberglass is out unless a secondary opperation is performed, just like I used to do - fiberglas skin back filled with dense polyurethane foam. Plastic molded with ribs is not enough and fiberglas just painted with mastic isn't enough either.
My waveguides are 6 inches across at the throat with a 1 inch hole in the center. They are so strong that you can take a sledge hammer to them and while the surface will dent, they will remain a solid structure. The waveguides that I see sold are certainly cheap, but they are also flimsy.