MartinLogan SL3 loudspeaker Page 2

The electrostatic element is curved in order to minimize the treble lobing that plagues the horizontal dispersion of panel speakers, where the transducer is larger than the wavelength it is producing. This beaminess created the notorious "one-person sweet spot" or "headphones effect" of older electrostatic designs. A large diaphragm projects a great deal of its HF energy at right angles to its surface; curving the surface in the horizontal dimension greatly facilitates treble dispersion—this was one of Martin-Logan's biggest innovations in electrostatic technology (see sidebar: "Controlling a Lightning Storm"). Tuning pads affixed to the diaphragm alter its resonant frequency, changing the single element into several smaller, better-controlled radiating areas. This prevents the diaphragm from having a single, lower (and therefore more musically intrusive) resonant signature.

Another way in which all Martin-Logans differ from earlier electrostatic designs is the way the transducer design has been pared down to the smallest possible number of component parts. The black metal screens that serve as the front and back speaker grilles are, in fact, the stators that drive the diaphragm. They are "conformally coated"; that is, insulated with a thick mask of specially formulated paint. Although they carry several kilovolts of potential, the paint is sufficient insulation to make them safe to touch—even at voltages far in excess to that any speaker will ever be subjected. Since this insulation covers all of the stators' surfaces, the diaphragm is protected from arcing when driven to high levels—unlike uninsulated electrostats such as my beloved Quad ESLs, which reacted disastrously one Thanksgiving to my wife's miscalculation of the peak volume of Vaughan Williams's Fantasia on a Theme by Thomas Tallis.

Like the Sequel, the SL3 uses a heavily damped 10" paper-cone drive-unit, this crossed over to the electrostatic element at 250Hz—but the SL3 uses a quasi-second-order 12dB/octave design. Sanders explains that eyebrow-lifting "quasi-": "We do some electrical lifting of the transducer because there's a natural acoustic rolloff below 500Hz with a dipolar source; we lift those frequencies slightly electronically to compensate. That means it doesn't have a pure 12dB/octave rolloff."

The bass bin's sidewalls extend to the top of the panel, tapering as they rise to focus the rearward wave of the electrostatic element—which also helps "lift" the bass response by preventing some small amount of dipolar bass cancellation. The result, Sanders claims, is a much smoother transition from the panel to the driver. "We were able to normalize the impedance of the speaker as a whole, which gives better low-level detail and superior blending of the 'stat and the woofer. The crossover design now optimizes the wave launch between the two elements."

The bass enclosure is another area where the SL3 departs from the Sequel. "We now have access to multi-axis CNC technology and special heat-set polymers that bind the cabinets absolutely rock-solid, making their resonant characteristics much more uniform," Sanders explained.

And despite the woofer cabinet's pebbly finish, Martin-Logan has abandoned Nextel finishes. "It's nasty stuff to work with—extremely toxic and very bad for the environment. We are now using a water-based coating that's easier to work with and far more benign."

The cabinet work is first-rate. The wooden rails flanking the speaker's face are coated with a clear lacquer whose lustrous finish is inviting to the touch, and the pebbled side and rear walls of the woofer enclosure have a high-quality if no-nonsense appearance. Component quality throughout the speaker is high—the transformers are custom-wound, and air-cored coils and polypropylene capacitors are employed.

The bi-wirable SL3 incorporates substantial metal binding posts of Sanders's own design. "I wanted something more rugged than the typical five-way binding post. Until the new European connector regulations came along, the spade had become the de facto standard in the High End, so I wanted something you could really get a wrench on and cinch down. The posts also accommodate bananas, but unlike with five-ways, we haven't drilled out the center post, which weakens it. I didn't even want to accommodate bananas at all, but our dealers use them for the day-to-day setup and teardown of systems, so I grudgingly compromised." Sanders's posts do allow you to crank 'em down hard, and the two pairs of posts are—for once—far enough apart to accommodate the widest, thickest spades I have.

Don't hesitate—bi-wire the SL3, even if it means you must use less expensive speaker cables. I don't know whether or not the woofer's back EMF interferes with the "unusually revealing" electrostatic element, as Sanders claims. But I do know that the difference between running the SL3 with a single run and a double run of cable is not subtle. Bi-wiring results in huge gains in clarity, detail, and grace.

Next to the binding posts is a Bass Control Switch with two settings: "Flat" and "-3dB." If your room is small, or if you must operate the speakers close to the wall, the -3dB setting may help integrate the drive elements better. (I didn't need it in my room.)

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