My intent is to stack (vertically) two 1" compression drivers on narrow or otherwise smallish 90-degree horns within the mouth of a 1x10" conical midrange horn of my own design, for line array purposes. Thus far, the horns available either obstruct too much mouth area, or don't span the midhorn's height for coupling to the next unit. (Using a pair of HF drivers per enclosure better approaches the "dense interference" tactic.)

I really don't want to change the mouth ratio by shortening the height. This has led me to consider the possibility of home cooking the HF horns, but the design needs to be simple, meaning no curved flares. Maybe adding a diffraction slot would work....