KLH model 9 electrostatic Speakers

Glad to have found this thread. I've owned KLH Nines since 1972 and driven them with Futtermans H3a and Marantz Model 9 I am still driving the KLH Nines with the same Futterman (recapped of course) and of the 3 pairs I've owned I've kept one and had it refurbished by David Janszen. I donated an early prototype (used 4 large bass panels instead of the 10 now used) I had as well to David as a gift. I drive the Nines with the Futterman or Accuphase. I've heard just about every Hi End speaker made since I love going to audio shows and owned Sound-labs A-3s and as well as still owning Modified zA2.1. Once you listen to a Nine its hard to forget them. The cords to the power supply cans make no difference at all.

@rdiiorio , you have been at it for a while! Most people back then though the SOTA was Marantz Model 9s driving K horns. If you were volume centric it was but if you cared about realism the KLH 9's were it. The only fly in the ointment is that the KLH 9's are not capable of realistic output and bass. It is hard to recreate the visceral side of music. ESLs do not project power well until they become full range line sources. The panels have to extend from floor to ceiling without gaps. Add subwoofers to such a speaker and what you get is the nuance of an ESL with the power and controlled directivity of a large horn. Currently only Sound Labs makes such a loudspeaker and it is darn impressive. 

Like rdiiorio, I've owned a couple of pairs of KLH9s since the early '70s. I worked in a high end store in Berkeley where a single pair of 9s could be heard powered by Marantz 9s, a hard combination to forget. The room--always critical to ESL setup--was well matched.  There was good bass to about 40Hz.  In bigger rooms, more 9s or subwoofers like the better RELs do the trick. The very low impedance of the 9s at low frequencies has always been a problem.  With one pair of custom built OTL amps which liked high impedance , series hookups of the 9s worked amazingly well.  The same hookup damaged another type of OTL.  Never a problem with transformer coupled tube amps like the Marantz 9s.  For a number of the early, fragile solid state amps, an RC network in series to roll off the very low frequencies gave protection.
Of all the speakers I've owned over the past 60 years, including Quads, Infinity Servo-Statiks, et. al., none has come close to optimally set up KLH9s.  Charlie Hansen of Ayre agreed.

Here is a link to an early pair of KLH model Nines showing a wholly different design in the amount of transducers used 5 verses 11, with 11 being used in final production units by KLH

https://ishaenterprisesllc.com/

Having owned the Sound-Lab A-3 I found using one segmented diaphragm to reproduce all frequencies was not as fast or natural sounding as compared to 2 or 3 pairs of KLH model Nine (series/parallel) driven by a Futterman, augmented with JBL B360/BX63A Sub/xover driven by a  McIntosh amp. Volume levels easily exceed 100db