What you can say about lowbass and midbass perfomance for high end loudspeakers ?

The design looks excellent. The crossover at 2 KHz means the mid range will be excellent and the off on and off axis response looks excellent because of this.

Not sure why they inverted the polarity in the ULF. I find this can create a disconnect between bass and mid range (our hearing is phase sensitive especially to 180 degrees changes in those lower frequencies as any one with a subwoofer can attest to and why all subwoofers have a polarity switch - there are also science papers proving this).

Looks like the transmission line bass has the Achilles heal of most TL designs - it is letting far too much higher frequencies get out - this will reduce mid range clarity.

https://www.stereophile.com/content/egglestonworks-viginti-loudspeaker-measurements

I agree with the philosophy - a large 12 or 15” woofer is only useable to a max of 500Hz. JBL large woofers (with the folded cones) go to 700 or 900 but they would break up in a controlled manner. I like Eggleston’s crossover points - they are close to where physics says they should be for optimal driver performance.

The idea of small woofers being "faster" is a myth.

What happens is more complicated and involves room acoustics as well.

Having said that, there are many speakers with dual 6" to 10" woofers which perform very very well in a room. See my threads on 2.5 way speakers.

IOW, I agree with the approach, but the explanation is an urban legend which hides a series of more complicated issues. 

Best,

E

Designers started moving aggressively towards multiple smaller diameter woofers driven largely by a desire to make enclosures narrower, a desire driven in turn by a desire to make speakers more self-effacing in domestic rooms.  The faster small woofer idea is an ex post facto "justification" for a trend/change driven by other considerations, of a less purely acoustic nature.

But smaller diameter woofers never get bottom low base compare to
big 10-12woofers., the reason a lot a top end designers still make
loudspeakers with big size woofers