I'm using a Fountek ribbon on top of the 3 Pi's as a supertweeter, and since the only cap in that crossover is a low value (1.0uF) I could afford an Audiocap Theta film and foil, and that upgrade made a world of difference compared to the Solen I started with. (It's much cheaper to upgrade the caps in a supertweeter tweeter that crosses over at 12khz than the one for the Eminence compression driver that crosses over at 1.6khz).

Do you recall I built a pair of 1 Pi Towers recently. I already had a matched pair of 10uF Northcreek Zens, so last week I upgraded the tweeter caps, and the difference is clearly audible. That change made a significant improvement in the treble smoothness. By the way, those speakers sound remakably good for the $200 it cost to build them. I wish I had room in the truck to bring them to the GPAF - after hearing them I believe Wayne might rename them the "One Pi Buttkicker Bass Option" and start offering the tower plans as an optional enclosure for the One Pi kit:)