Herman wrote: "Macro, you should look into getting a true horn for that compression driver. What you have looks more like a megaphone than a horn. I don't doubt you are pleased with the sound from it but I wonder what it would sound like with what I would call a true horn."
The horns Bill Woods makes are conicals, which are onstant-directivity type. Equalization is essential with a conical (or any other constant-directivity horn); if not equalized properly, it does indeed sound like a megaphone. But once equalized properly, they have a very desirable characteristic. Let me explain:
A compression driver all by itself (no horn) will have a very wide pattern at the lower end of its range and a narrow pattern at the upper end - just like any direct-radiator piston. When this output is forced into a constant angle by a conicial horn, the result is over-emphasis of the lower end of the driver's spectrum (megaphone effect). Without the horn, the response was good on-axis, but poor off-axis; now with the conical horn, it is equally bad both on-axis and off-axis. But this is actually a window of opportunity - when we fix one, we also fix the other! So we equalize in the crossover, and now not only is there no megaphone effect, but the sound is quite uniform across the entire angle that the horn covers. In my opinion this is very desirable and well worth all the trouble we just went through, as now the reverberant energy will have nearly the same spectral balance as the first-arrial sound (a characteristic of live voices and instruments that most speakers fail to emulate).
One very slight downside to a round horn is that the horn's mouth reflection is equidistant from the central axis, which results in an on-axis dip. The location of this dip varies with the diameter of the horn and the listening distance. But the fix is quite simple: Listen from about ten degrees off-axis, and the dip disappears.
Duke
