Chances are you've read or heard at some time that adding a subwoofer to a system built around electrostatic speakers ruins the sound. Although that's not necessarily true (and we have the subwoofers to prove it), the idea is grounded in experience. For many years subwoofers and electrostats did not mix very well. Turn on the sub and maybe you got the deeper, stronger bass you were looking for when you bought it, but suddenly that wonderful electrostatic snap and midrange clarity were, if not gone, at least subdued.
Our goal when we started working on subwoofers was to make them do all the good stuff – deeper, stronger bass, essentially – and none of the bad. We wanted to build subwoofers that when you put them in rooms with electrostatics and turned them on, the sound stayed exactly the same except now it had a better low end. Descent is the most complete expression of the years of work MartinLogan engineers invested in making that happen.
Although a lot of elements (detailed below) are involved in working Descent's magic, the most important are its TriLinear™ BalancedForce™ driver configuration and its very sophisticated servo control system. TriLinear BalancedForce places three drivers – high-performance 10-inch aluminum-cone units in this case – precisely 120 degrees apart from each other on the cabinet. As a result, their reaction force vectors exactly cancel, virtually eliminating cabinet resonance and vibration. Gone with them are the cabinet-radiation coloration and bass blur that afflict even the best conventional subwoofers at a subliminal level. The servo system, meanwhile, takes care of business with the drivers themselves, ensuring that their output – the output we want – is always an absolutely faithful replica of the audio input signal.
Descent is a beast, but a beautiful, athletic beast. Why take a woolly mammoth home when you can have a cheetah?
Descent's high-resolution driver combines a 10-inch aluminum-cone diaphragm with a high-intensity magnet structure to achieve huge excursion and output capability without sacrificing detail. By eliminating cone flexure, even at long voice-coil excursions, aluminum diaphragms help our advanced-technology bass drivers achieve the very low distortion necessary for proper blending with MartinLogan electrostatic speakers.
All dynamic drivers have nonlinearities in their suspension and motor systems, which increase dramatically at large diaphragm excursions. The resulting distortion can rise to 20 percent or more with typical woofers and subwoofers reproducing strong deep-bass signals. MartinLogan's advanced servo system uses a sophisticated monitoring and control circuit to detect and instantaneously correct any deviation between acoustical output and electrical input. The result is a three- to ten-fold reduction in distortion for the purest possible low-frequency reproduction.
Each of Descent's 10-inch aluminum-cone drivers weighs 8 pounds and has a maximum peak-to-peak excursion of 1.2 inches. That works out to a total displacement of 30 cubic inches – typical for most high-quality subwoofers. Descent has three of these drivers, however, yielding the equivalent acoustic power of a 24-pound driver with a maximum peak-to-peak excursion of 3.6 inches and a total displacement of 90 cubic inches. Moreover, each of these drivers is individually servo controlled for absolute minimum distortion. The single-driver alternative would be an extraordinarily robust 18-inch unit, which by virtue of its size and very long excursion would inevitably generate considerably higher distortion. Descent enjoys all the advantages of the smaller, more refined drivers while achieving the output capability of a huge 18-inch driver.
Conventional subwoofer enclosures vibrate in reaction to driver activity, creating a secondary and highly colored sound source. In extreme cases, the cabinet may even "dance" on the floor. The typical expedient of adding mass can make the problem less obvious, but it doesn't really make it go away. Resonant bass smear is inevitable unless cabinet vibration is drastically attenuated. MartinLogan's BalancedForce design places multiple drivers in exact opposition to one another, so that their forces on the cabinet almost perfectly cancel.
Descent employs a novel BalancedForce configuration, in which three identical drivers are spaced precisely 120 degrees apart on the cabinet. Their reaction force vectors exactly balance at the center point for near-total cancellation, reducing spurious cabinet radiation by as much as 25 dB (a power factor of more than 300:1).
At very low frequencies, all rooms exhibit a phenomenon known as room gain, which produces a mild bass boost. The smaller the room, the higher the frequency at which this starts. Descent's 25-Hz level control enables you to compensate for excessive room gain by cutting output in the 20- to 30-Hz range or, if you prefer, to accentuate the feeling of deep-bass energy by augmenting those frequencies.
Descent offers switch-selectable low-pass crossover frequencies of 40 and 70 Hz, implemented with filters precision-designed for optimum attenuation slope and minimum group delay. The 40-Hz filter is tailored specifically for MartinLogan and other floorstanding loudspeakers, while the 70-Hz filter is tuned for bookshelf, center, and surround speakers. This ensures cohesive integration with smooth response through the crossover range with any type of main speaker.
Descent's amplifier belongs to recently developed class of switch-mode designs that incorporate a variety of innovative techniques to reduce noise, distortion, and heat to the lowest possible levels. In particular, the switching frequency is much higher than in typical subwoofer amplifiers of this type. It can produce a true 400 watts continuously (800 watts peak) with total harmonic distortion (THD) of just 0.07% at all levels.
Although ports are a convenient and cost-effective way of increasing low-frequency output, they rely on resonant energy in a way that impairs bass quality. A good sealed system will exhibit less transient-blurring group delay while maintaining smooth, consistent response regardless of output level or voice-coil temperature. Listen carefully to the sound of a bass drum, and you'll hear the difference.
Audio and video products available today represent a confusing myriad of connection options and setting configurations. Understanding this complexity, MartinLogan's team designed the Descent with an input architecture that easily integrates in both stereo and home theater systems. LFE input effectively uses no low-pass filter, instead leaving crossover control to the processor. Left/Right line level inputs integrate an audiophile grade 40 or 70Hz low-pass filter. RCA output allows multiple Descents to operate in a serial configuration.
For home theater systems in which the surround processor supplies the crossover, Descent provides an LFE input that completely bypasses its internal filters. It also has an unfiltered line-level output to allow operation of multiple subwoofers in a serial configuration.
The Descent is supplied with sturdy, 3/8-16 ETC™ spikes, which can be used in place of the standard feet to enhance stability on thick carpets or to create tighter coupling between speaker and floor.
Let's face it – most subwoofer cabinets are just nicely finished boxes. That leads people to hide their subwoofers in corners behind plants or to buy models that look like end tables. Inspired by its three-driver TriLinear™ BalancedForce™ configuration, Descent's hexagonal form is both visually engaging and easy to integrate into a room. Descent also features a quick-change wood-finish top, which enables it to blend into any décor.