What can anyone say about Quarter Wavelength transmission line enclosure design ?

Of course, those are being actively bi-amped.  Only producing between 80 and 20Hz(60dB/Oct cutoff).   

Too bad you can't hear my pair, regardless of what I type(8', tapered, folded, w/10" Seas L26RO4Y D1004) .   Are you ever around the Indianapolis, IN area?

@erik_squires - Experimentation(a lot), back in the early Eighties and DSP, now. Wasn’t all that hard!

@millercarbon- Did you happen to find that design in the Speaker Builder Magazine articles(circa- early 1980’s), written by Roger Sanders? In them, he outlined building a 10", TL woofer system, closely matching your description, to compliment his(then home-built) electrostatic panels.

That, Glass Audio and Audio Amateur, were my favorite rags(back in the day).   Inspiring!

I built a pair (in 1981), per Roger’s design, to go with a customer’s Acoustat Model IIIs. He wanted something that could match the speed and definition, of his electrostatics. They worked so well, powered by a Halfer DH-500 and crossed over via a Dahlquist DQ-LP1, I duplicated the system for myself(and my Acoustats) and another customer. Back then, I used a 10" woofer that Milo Nestorovic employed in his woofer systems. In answer to the OP’s original query; TLs(at that time), were the only woofers systems around, that many of us had experienced, able to blend well with electrostatics. I used bi-amped TLs, in concert with various planars, for 36 years. Now, with an Emerald Physics system. The trusty DQ-LP1 was replaced by a modded TacT RCS 2.2X(and Hafler Trans-Nova 9505), about 12 years ago. The TacT’s DSP(time-alignment/room correction/EQ) was the finishing touch, to an already stellar bottom end. Guess I’m a TL believer!

Fried, and his IMF(Irving M Fried) designs, got me interested in TLs.  Man; that's been awhile(I'm dating myself).

@millercarbon- Affirmative. Built three pair of those. Excellent, extended, authoritative, articulate and tuneful bass. The system did a good job of extending the dynamic range of the electrostatics too, relieving them of the longer excursions, demanded by the bottom freqs.

These ARE, by definition, "transmission lines" and have been found wonderful designs for bass reproduction, by the experienced and dedicated. http://diyaudioprojects.com/Technical/Papers/Non-resonant-Loudspeaker-Enclosure-Design.pdf Good stuff, regarding why they work so well, for the knowledge seekers: http://www.quarter-wave.com/TLs/TL_Anatomy.pdf