There's a couple of versions floating around. One for 2" exit and one for 1" exit compression drivers.

I built a clone of the JBL 2397 horns and use them with my 2445 2" exit drivers. They're crossed at 800Hz to 15" 2235 woofers. The horns and drivers tend to rolloff just below 10KHz, so it benefits from a supertweeter. Can't really expect a 2" exit compression to extend out to 20KHz.

The small smith horn, dubbed "1200Hz Smith Horn" was designed for 1" drivers. You may have to rework the crossover, but this horn may replace the plastic horns used on Pi Speakers.

gar.