Hello Duke, can you comment on the benefits of using round wave guides as opposed to the rectangular type?
The pattern from a round waveguide is axi-symmetric like that of the woofer, but the lack of such symmetry in the rectangular one can be compensated for in the crossover region. The round one results in more energy in the early floor and ceiling bounce reflections, but the energy in those reflections will be spectrally more similar to that of the direct sound. A round waveguide has a deeper axial dip from the mouth reflection, whereas the dip is spread out enough to pretty much eliminate it with the rectangular format - but that is of academic interest only if you listen more than 10 degrees off-axis.
How does the size of the wave guide relate to the size of the lower hz driver?
For good pattern control down to the crossover frequency, the width of the horn or waveguide should be comparable to that of the woofer. A rectangular horn starts to lose pattern control in the vertical plane above the crossover frequency, and this has to be taken into account in the crossover design.
I noticed that you use both depending on the speaker design. However, Earl Gedlee only uses the large, round type.
In my opinion the round waveguide is the ideal, but I believe that I can come close with the less expensive over-the-counter rectangular model. Apparently with the waveguide-style horn I use, it is still possible to avoid characteristic horn-signature colorations - or at least that's the feedback I got on my room at Lone Star Audio Fest. I had several people there begin conversations with me using these words: "I hate horns, but...".
Sorry for the brevity of the answers, but trying to get ready for RMAF and get some speakers shipped to customers before leaving for the show.
