Wayne,I would like to put a Edgar Horn on top or within a Pi3 or 4. What works better? I imagine the horn looks best on top. I suppose the Pi 4 has more kick in the bass. So many choices.
My listening room is 12x24x8 and cluttered and I have a ASL ultra-linear PP with EL34's. I have DIY folded TQWPs with RS40-1354 drivers. They're directional, and not too bad. I was told that the setup is mismatched. I haven't tested this judgment out.
At any rate I'm about ready to take on another project. May I look at the Pi4 plans?
One more discovery; I was looking at the Eminence 10, 12 & 15 coax's and they can't beat your price, or the performance I imagine.
Thanks, Ron