There's a particular kind of audiophile who spends years chasing the Quad ESL-57 — that wafer-thin slice of midrange heaven from the late 1950s — and eventually has to admit the truth: it can't play bass. Not really. It goes down to maybe 45Hz on a good day, in a well-treated room, if you're asking nicely. Below that, it simply politely declines.
Martin Logan spent a good portion of the 1980s and 1990s figuring out what to do about this problem, and the CLS line was their answer. The original CLS dropped in 1984 as a full-range electrostatic — no dynamic woofer, no crossover, just a single curved panel the size of a road sign doing all the work. It was extraordinary. It was also, in practice, maddening to drive.
The CLS IIz, which ran through the 2000s and saw its last major iteration around 2010, is where Martin Logan finally made the peace. They added a powered 12-inch woofer in the base — 200 watts, internally amplified, with a variable crossover you can dial in — and suddenly you had an electrostatic that could actually pressurize a room.
What It Actually Sounds Like
The panel itself is still the story. That enormous curved diaphragm — a few microns of Mylar with conductive coating, stretched between stators and biased to several thousand volts — moves in a way no cone driver can replicate. There's no mass to overcome. The music just appears. Transient attack on a brushed snare or a plucked guitar string is something you don't forget once you've heard it.
What Martin Logan understood better than most was that the curved panel also helps with the electrostatic's biggest weakness: the figure-8 dispersion pattern that makes them murderously position-dependent. Toe-in matters enormously. Get it wrong and you're listening through a keyhole. Get it right and the soundstage opens up in a way that makes conventional box speakers seem like they're wearing oven mitts.
The powered woofer crossover sits around 270Hz, and the IIz version cleaned up the integration considerably compared to the original II. There's still a slight textural discontinuity between the panel and the woofer if you're listening for it — the dynamic driver doesn't quite have the same speed as the electrostatic membrane — but in practice, with good source material, it's not the distraction you'd expect.
These things demand amplification. Not just power, but current. They present a load that drops to under 1 ohm at high frequencies, which will make a tube amp weep and a lesser solid-state amp shut down in protest. You want something beefy and stable — a Bryston 4B, a Krell, a Pass Labs X-series. Feed them garbage and they'll tell you. Feed them well and they'll tell you that too.
The honest caveat is humidity. Electrostatics and moisture are not friends. The panels can arc in very humid conditions, and over time the coating can degrade. Buy used and you are buying someone else's climate-controlled basement habits, or lack thereof. Inspect carefully. A re-paneling from Martin Logan is possible but not cheap.
At $2,500 to $4,500 used, you're getting something that was north of $10,000 new. For that money you're living with a speaker that has maybe a 9-foot sweet spot and weighs 80 pounds per side and needs its own dedicated circuit. Everything about this is unreasonable. The sound makes it reasonable.