MartinLogan Descent subwoofer
ML speakers mate quite nicely with subwoofers from other manufacturers, especially large Velodynes, and years ago I read enthusiastically about the wondrous pairings of the all-electrostat, all-the-time Martin Logan CLS panels with the large Muse Model 18 subwoofer outfitted with a "personality card" to properly consummate the relationship. So why would MartinLogan choose this time of unprecedented popularity for their hybrid speakers to join the already-crowded subwoofer field? Well, I'd say it's because Gayle Sanders now has something good to say.
Look Ye, Look Ye
Three 10-inch-diameter servo-controlled aluminum cones firing horizontally and 120° apart, 400W RMS, and a neon-blue zig glowing above the front grille—sounds like one of the tricked-out NOZ cars in The Fast and the Furious. But I'm describing MartinLogan's new Descent powered subwoofer. Its hexagonal shape is the first indication that this isn't your Daddy's Oldsmobile. The punchy drivers have high-excursion surrounds—when I pressed them with my finger, they felt tight, which I hoped was a harbinger of what was about to come.
Those three symmetrically opposed drivers, a design ML calls BalancedForce, are arranged to combat Newton's Third Law: for every action there is an equal and opposite reaction. In a more normal speaker, when a solitary driver in a box vibrates, the force of the piston moving in and out creates opposite reactions within the cabinet, causing it to vibrate as well. As a result, most subwoofers make very poor surfaces for displaying your ceramic figurines. Because the Descent's woofers operate in phase and are arranged axially 120° apart, the reaction of the cabinet to each driver's motion is nullified, by the action of the others. MartinLogan suggests that this eliminates the bass muddiness that can result from this motion.
The Descent's three drivers are each mounted on their own baffle with a removable grillecloth. The front baffle, the one most people would choose to fire forward into the room, also houses the subwoofer's controls. Power can be set to Standby mode, Always On, or Auto, which lets the sub rest in Standby and turn itself on only when it detects a signal. In my experience, auto-detection circuits often begin failing or cutting out too early or too often, as if my monthly electrical bill were directed to them. Fortunately, the Descent's Auto mode has behaved itself well for the few months I've used it.
Many subwoofers include low- and highpass filters and pairs of speaker inputs and outputs for use in a 2-channel rig. In this case, you connect the amp's outputs to the sub's inputs and the sub's highpass outputs to the amplifiers driving the main speakers. The sub's lowpass filter limits the frequencies it must reproduce, and the highpass filter prevents those low frequencies from getting to the main speakers and potentially affecting their dynamic capabilities.
The Descent has no highpass filter. In a 2-channel system you would connect the preamp's line-level outputs to the sub's L/R RCA line-level inputs and the main-channel amplifiers in parallel, using two pairs of outputs (if your preamp is so equipped) or a pair of Y cables. The sub has a lowpass filter (with a crossover selectable at 40Hz or 70Hz), which keeps its signal in a useful range, but with this setup the main speakers receive the full range, including low frequencies they might not be able to handle.
This caveat is moot if you plan to use the Descent in a home theater, where your processor will provide both low- and highpass filtering as needed. For us home-theater buffs, the Descent's two LFE inputs—one RCA and one balanced XLR—are the way to go. If you want to daisy-chain multiple Descents, you can, but only via the single-ended Subwoofer Out connection—a balanced XLR sub out is not included. However, given the performance of even a single Descent in my very large home theater, this isn't nearly the oversight it seemed at first.