I'm planning to build a horn like what you're talking about to go with my 12π horns. I'll probably use a driver like the Eminence Magnum 12 or JBL 2206 mounted on a horn. Models show a 3 foot conical horn with ~30in2 throat and ~400in2 mouth should do nicely.I have my hands full right now, but probably in the first quarter of next year, I'll be building some prototypes. I still have most of the work ahead of me for the 12π horns, and might make a newer 10π as a scaled down version of the 12π using HL10s. Both of these will need a horn to cover the range above 100Hz. The smaller midrange horn that I use in seven π and eight π speakers is too small to reach down to 100Hz. So I plan to make a horn that uses Magnum 12s or 2206s to cover the range.