Neill,
I own Fostex F200A based TL speakers (Bob Brines designed/built model FTA-2000, Martin King inspired) and drive them with 40 watt chip based monoblocks (Channel Island Audio from here in the States). The F200A are single driver, not co-axial (they have an aluminum dust cap, no whizzer, and are 20 cm across) so they may appear to be coaxial. They carry a huge AlNiCo magnet and so are very musical (and quite "dark" compared to most extended range drivers that are better termed midrange/tweeters). Other single driver fans have been dumbfounded by the deep bass possible from these speakers.
I'm a "speaker guy" and an amateur "theoretical purist", so the single driver approach really appeals to me. My first audio ephiphany occurred while hearing mass loaded transmission lines in the 70s. The depth, speed, power, and musicality of the bass amazed me. The coherent sound and simplicity of single driver designs combined with the advantages of direct amp/driver (active) coupling covered the other two audio ephiphanies I've experienced. So I shopped quite a bit for these "destination" speakers and ended up commissioning Bob to "invent" and build the first pair. At 20 cm and no whizzer they beam, but they are in my "man-cave" with all serious listening done nearfield from "the" chair, so no worries. IMO nearfield listening almost requires single driver speakers (or headphones
).
Yes, ultimate output is more limited in most single driver designs, but the bigger/more efficient drivers provide quite servicable sound pressure limits (at least for these 50 something ears). The Jordan 92 have been around for decades and used in nearly every imaginable type of speaker design. Their aluminum foil cone (intended to flex to provide improved high frequency response) is unique. But many have been critical of the published specifications as overly optimistic. And they're not inexpensive, especially here with the weak USD.
With extended range drivers efficiency typically goes up with size. My F200A are an exception, but OTOH they are rated "raw" down to 30 Hz. While rated at about 90 dB/w/m and to handle 27 watts constant, 80 watts peak, a pair in a "normal sized" room should reach 104 dB constant and 109 dB peaks which is plenty for me. Bob Brines is a lover of the Baroque so they do acoutical and small ensembles, but also handle symphonic and rock (without that fatiguing edginess). In fact Led Zep was amazing a few days ago with deep/forceful bass and many newly discovered nuances in the music.
Transmission lines have several other advantages. The typical sloping interior vents internal reflections away so they that don't re-emerge back through the driver(s) to smear the sound. The normal internal baffles provide cabinet bracing. They recognize and take advantage of the pipe resonances created by typical floorstanding cabinets with their relatively long/skinny internal chambers. Internal pressures (and therefore cabinet colorations) are reduced. The bottom end impedance rise is smoothed out and with bass response is extended deeper and power amps "see" an easier load. Bass roll-off is at a 6 dB/octave rate that matches natural room gain to optimize performance.
So if you have the Jordan 92 VTLs, I'm sure any of the AKSA amps would do fine for "civilized " ening (no block parties). If you don't have the Jordans yet, you might want to shop around. BTW, Bob Brines offers plans, panelized (pre-cut) kits, assembled raw (unfinished) cabinets, or fully assembled speakers at very reasonable prices. OTOH I'd love to hear the new AKSA speakers.
