I recently built a pair of three-way cabinets, using the Air Motion Ribbon tweeter mentioned in post #26, a pair of SB Acoustics 5¼" mid-woofers and a 12" subwoofer.
I also designed the passive crossover, using a second order filters between the sub and the mids, and for the mid-high frequencies, a second order filter on the mid-woofers and a third order one on the tweeter. The crossover in a speaker design is as important as the drivers. You can have the best available drivers, but combine them with a poorly designed crossover, you will never get a good performance.
This speaker pair was presented to the Montreal Audiophiles Association, and I received excellent comments after the presentation and a warm applause. One of the members, who had of course heard many loudspeakers over the years, told me that my speakers were with from another pair of speakers, the best speakers that he had ever listened to.