Werticus,
JohnR pretty much covered it. His first entry is Lukaz's long lost website, which I'd been unable to locate when he moved it.... (thanks John!)
Many of Lukaz's projects a classic 3 ways, with dipole midranges, much like my decade old Alon IVs.
Besides its appeal as a passive xover, it also facilitates straightforward implementation of multi-amped line level crossovers. As excellent midranges and tweets are available with efficiencies north of 94db (PHL, Audiom, Audax) its feasable to drive the mid-tweets with a minimal feedback high output impedance tube amp (a 'hard' amp), using a line level as the mid higpass and passively implementing the mid-tweet xover.
Similarly, the woof can be directly driven with a line level lowpass for maximal control. The caveat here is the overlap between the woofer and the mid. At a transition frequency of 350-550hz differerences between amps can be significant (I am painfully aware of this in passively bi-amping my own Alons) You really do need an excellent ss amp iff'n you're going to mix sand and hollow state... The Aksa 100N works a treat.
As John's and other urls will also show, some folks are also implementing passive dipole 2 ways, requiring substantially wider baffles, and high Qts drivers for a bass respones into the 50s. WAF constrains me to the prior approach.
http://www.diyaudio.com/forums/search.php?s=85e4e609f8ccf7f1c8a684f68f59d625&action=showresults&searchid=560662&sortby=lastpost&sortorder=descending
