Pdprez, good call - I hadn't made a mental distinction between "horn system top-to-bottom" and "horn system over part of the spectrum". And your understanding of my designs is correct; you also get extra points for coming up with the right name for one of them!
I have no hands-on design experience with top-to-bottom horn systems, and would think that they'd be far more difficult to do well. I'm too chicken to even try.
Weseixas, a waveguide (as Earl uses the term) is a type of horn optimized for low coloration and well-controlled off-axis radiation characteristics. If you're willing to distinguish a Geddes-style waveguide from the rest of the horn world, then you and I are quite likely to end up on the same side here. And what fun would that be??
Cheers,
Duke