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.
KLH model 9 electrostatic Speakers
I just bought the above speakers, I like them a a lot , I am thinking if it’s possible to replace the power cord on the power supplies. On this speakers? Thanks B