I built a double 15 with a eaw la 325 waveguide horn a while back, along with faital pro fx 560 15's. I found the eaw waveguide to be one great sounding horn when listening to it. This is compared to my jbl 4733's.
So for the heck of it I wanted to try something else. Built the same Identical box but used a B+C me 90 and a Radian745neopb. Right off the bat it sounded much better then a Jbl horn, but something wasn't right. When comparing the B+C and raidian to the eaw waveguide my new experiment sounded bright in places, some comb filtering was going on, it just seemed a little harsh. So what was the culprit here?
I then bought a faital pro lth142 horn, its not a constant directivity horn but designed like the eaw wave guide. No harsh angles all smothe, eliptical? I bolted the Raidian driver to the faital horn and installed it in my box. I used this setup last night and problem solved! Even coverage, no harshness, no combing.
So I guess what I'm getting at is if your looking into building some box's, look away from the CD horns.
FaitalPRO - Professional Loudspeakers Made in Italy
Radian - 745NEOPB