08-06-09: GriffinconstI'm very familiar with all the speakers you mentioned except the L810. I owned both L880s and L1090s.
Along the same line, how about a/d/s 810 or 880? Were they in the same league as the Dahlquists? I've heard the soft dome mid is SWEET.
Just to be clear, I wouldn't spend $1000 on the used speakers but wondered if they compare to the sound quality of $1K new ones.
ADS's quality rested in high quality driver design and meticulous quality control over their fabrication. Their quality driver enabled them to create speakers with wide frequency range and linearity out of--at most--3 drivers. When it came around to designing loudspeaker systems, their designs had the advantage of incorporating high quality drivers with broad operating ranges into similarly high quality, inert, sealed cabinets.
By contrast, the DQ-10 was the opposite--taking low-cost drivers and stringing together enough of them to achieve reasonable linearity over a broad range. That's why they ended up with a 5-way that still screamed for a sub (which came along later). Each driver on average only had to operate over a 1-1/2 octave range. Dahlquist's significant contribution to speaker design was mounting all but the woofer on open baffles and aligning all the voice coils in a single plain for phase coherence among the drivers. The open baffles were sized as large as necessary to avoid rear wave cancellations and as small as possible to avoid diffraction distortion. This made for a very linear speaker for the time with phase and time coherence, something virtually unknown at the time, though ADS speakers also had uncanny soundstages and imaging.
The DQ-20 is fundamentally a better speaker, as it retained the open baffle phase coherent design but went down to a 3-way, meaning it achieved linearity with better drivers that had 3-octave operating ranges on average. It was the first design by Carl Marschisotto, who went on to found Alon and then Nola, and you can see the family resemblance in the DQ-20.
The downside (and upside) of the ADS is the sealed woofer(s). This makes the bass cleaner, tighter, and with a gentler roll-off than a vented enclosure. It also means the roll-off starts at a higher frequency and big, high current expensive amplifiers pay off with better bass extension.
The downsides of the DQ-10 are low sensitivity owing to the open baffles and the 5-way network, the woofer whose foam crumbles every 10-20 years, and the $1.50 piezo-electric super-tweeter which isn't the last word in smoothness or linearity. Fortunately, it just adds some top-octave air.
You must remember that at the release of the DQ-10, the Bose 901 was still considered a high end speaker, as was the JBL-100, the Altec Voice-of-the-Theater, and some pretty honky-sounding JBL floor-standers. Other new companies that sought to make a true high fidelity speaker included Infinity, ESS, Ohm, Advent, and EPI.
Overall, at $1k for today's speakers, I'd probably choose a PSB Image T55 or T65, Ohm Walsh MicroTall, or Energy. These would have more sensitivity, more bass extension, and easier dynamic range with less demand on the amplification. OTOH, an ADS L1290, 1590, M12 or M15 would still be a fabulous speaker if you bi-wire or biamp them with a powerful high current amp. E.g., Telarc used Threshold Stasis class A amps to power their L1590s.