Nice to see some DIY speakers, carefully made.
My 'perfection list' for speakers is different, but I'd be interested to know if it overlaps anyone elses. day to day I listen to some Usher speakers, with 8" mid-bass, so this is thoughts: real world gets in the way!
I like the drivers as close together as possible. Ideally coaxial, like posh Tannoys.
The crossover point of 2.5kHz is quite sad, as that's the critical listening area, so IMO that should be avoided...
... as should real crossovers: the crossovers should be in a small box of suitable electronics with small components. A separate amp should drive each driver, ideally tube class A for treble and mid (if 3 drivers), and possibly a class B transistor won't be able to mess up the bass so it might be OK there.
Once that criteria is done: bass should be in a sealed box, of suitable shape, rigidity and wool stuffing. Ports are 'cool' and useful, but flapping a cone further than required gives IM distortion and the phase gets all messed up anyway.
12" bass is useful for that reason too: It doesn't have to move very far, as the surface area is a reasonable size, so dynamics are effortless.
I've actually had quite nice results with a single paper Eminence 12" Beta and a Motorola horm tweeter, not even biamped, the combination has a nice 'immediacy' to it, none of the cloying 'polite' suppressed sound of todays hi-fi shop offerings. For this reason I like the sound of whizzer cone paper speakers, with a supertweeter for the top, close by: for vocals and realism this is very nice.
Of course Alnico magnets help too: some of the well built tube table-top radios with 6" alnico speakers in them sound so spookily realistic on speech, you'd swear someone else was in the room. Think about it: Class A tube, Alnico speaker - paper (with possible whizzer) and a fully tube tuner and peramp section: we've gone forward in many ways with HiFi, but not always toward the direction of accurate sound.
To a large extent I blame the bogus THD measurement (The 2th harmonic really isn't as important as the 7th), terrible class B transistors fighting poorly understood global feedback loops: and of course the 'cable guys', who turned the persuit of sonic accuracy into a freakshow.
Which reminds me: ACF50 oil: All of the speaker connections, RCA connections etc: add a drop of ACF50, you'd be surprised how over time the metals corrode and start forming little semiconductors