Hi Mark;
Glad you asked! I have a 3 way system electronically crossed over by a mini DSP. HF is handled by 8 planar tweeters driver by a Yamaha P2200. MF speakers are self-designed line arrays, 16 drivers per cabinet, 5 1/4" each. The drivers are very slightly over-lapped to reduce the centre to centre distance. I feel that my design has some merit because the over-lap allowed use of larger drivers that could then be crossed over at 150 Hz. The over-lap also allowed an upper limit of 2 kHz, before the line effect was lost and the drivers behaved like point sources with the associated interference patterns. The MF line arrays are currently driven by a PL 700B with a White Oak board. I hope to rebuild the PL 700 series II full-complimentary for the MF's.
My goal was to build a system that is High Fidelity, but can reproduce rock-concert levels. I built LF cabinets which are basically copies of JBL cinema subs. 1" MDF was used, as well as another minor improvement; a front protruding duct. I hesitate to suggest that I could improve on a JBL design..............however; a ducted port cabinet tends to develop a different (momentary) static pressure, (and resultant cone off-set) due to 'pumping', or the difference in resistance to air motion (in verses out). This is caused by one end of the duct terminated in free air, and other end terminated at the cabinet face. I believe that a 1 & 1/2" forward protrusion may help. I could then use a larger diameter (and subsequently longer) duct which would reduce 'whistling'.
I used RCF 18" drivers which have a maximum P to P cone excursion of 50 mm (2" !) The RCF's had very similar parameters as the JBL's used in the cinema subs, but claimed 97 db/ 1 Watt @ 1 Meter, 2 db less than the JBL's. This would prove to be expensive. The LF's sound and feel great, the lower tuning point is 19 Hz, but my old PL 700 was not able to get the maximum 'punch' out these woofers. From my limited research, it seemed that the Crest CA-18 had respectable specs---and monstrous power: 1000 Wpc into 8 ohms.....so when the wife was not looking, I bought one. Pink Floyd can now almost blow out candles at 20 feet! There may some finger wagging here, at having a class H amplifier in a so called "HI FI" system, but this amp is crossed over at 150 Hz and down. It did however, take a few months to get this amp civilized enough for home use. The S/N ratio was good, but the amp itself was noisy. It took 20 dips of the toroid transformer in electrical varnish and much lower cfm fans to be able to live with the amp in my listening room.