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Aries Cerat Gladius. Due to their far cleaner sealed loading over any of the ubiquitous but always resonant ports, these premium 12" Fostex woofers look more hung than they are. During their review Wyred4Sound's potent mAMP ICEpower monos had squelched any secret desire for subwoofer augmentation. Returning to my SIT1 monos the lust arose again from simple contrast. This gets us at the lesson embedded in this particular trial. If you prefer very simple no-feedback amps for their reduced number of gain stages and non-paralleled output devices, you could give up raw bass drive with low power and higher Z-out. Amps sufficiently potent to dominate your woofers into max control meanwhile might not have the overall sonic purity and sophistication you crave. What to do other than change speakers?

Here a subwoofer of Zu's caliber can add the missing extension without messing up an iota in the remaining nine octaves. On Amir John Haddad's brilliant 9 Guitars Flamenco album for example—he plays a different instrument on each track to make for a crash course in guitar tonalities—adding the Submission also added floor resonance below the dancer's rhythmic zapateado footwork. On the rollicking "Al-Mawsili" which is described as a jaleos abandolaos with brilliant turns on the Arabian oud and bouzuq, not only the bass accents grew in power but so again did overall scale. The proper word is gravitas. Admittedly far less of a change than the sub-completed Wave transformation because the Gladius solo is good to about 40Hz even with SIT1, it nonetheless was a well-appreciated advance. There is plenty of life below 40 cycles.

Key for me was that I gained extension which the Wyreds had mostly achieved already albeit without buying into their denser wall-of-sound gestalt. I really love the SIT1's specific inside-out dimensionality. It's that self-revealing spaciousness which doesn't force me to penetrate any thicket of things from the outside in. That again ruled. I was back in small-amp lucid mode but with big-amp bad-ass bass reach and power. Sonically it was something for nothing - all gain, no loss. Financially there were considerable losses but that's par for this course.

And here's something vital. I've heard reasonable arguments about how combining disparate amplifier technologies like class A on top with class D on the bottom is a proven recipe for audible discontinuity. If we dealt with the usual THX-style 80Hz transition point, I'd feel far more compelled to concur or at least call it very likely. On my desktop, the ICEpower Wyred4Sound mINT did in fact make for the texturally more cohesive combo with the Gallo Strada 2 and its companion class D-powered TR-3D subwoofer than April Music's class A/B Aura Vita integrated. Moving the transition point down by an octave however changes the game. Be it because our hearing in the first octave is less keen or because class D nine out of ten times is simply better equipped to deal with infrasonic woofer control - the results really speak for themselves. Whilst the arguments against it sound reasonable to logic, they don't hold up in the listening seat.

At this point, reader Brian Livingston wrote in: "Your findings on subwoofer use concur with my own. For the past two years I've been using two large SVS closed-box subs with 13.5" drivers and class D amps. Previously I used two $500/ea. Cerwin Vega subs. My upgrade to the big SVS units at $2.000 each was a huge improvement. I tried various crossover points recommended in various articles in the 60-80Hz region. None of those worked and only created bloated bass. Then I moved down to 40Hz and finally 31Hz where they presently sit. My system consists of the Bakoon AMP-11R (thanks!), NAD N51 DAC, Mac mini/Audirvana in integer mode and open-baffle panels with ten 5" widebanders hinged in the center in a V configuration so each driver is equidistant from the listening position to make for superb imaging. But bass output from these panels is barely acceptable without subs.

"I find the use of the Bakoon which has its own volume control to be of great assistance in achieving the perfect overall system balance. The NAD N51 DAC has its own very very good volume control. Whatever speakers you use in this system, you can change the balance according to their output and efficiency. I set the sub outputs to ~80%, the Bakoon to ~50% and then use the NAD's volume as the remote-controlled master. As you stated in your findings, soundstage scale, musical body and definition all improved immensely. Recordings of especially classical suddenly had clean low tight bass which was never available with the crossover points set between 60-80Hz. Conclusion? One can achieve system balance virtually unattainable with any of the conventionally high settings of subwoofer crossovers."

Rethm Saadhana. With this Indian widebander good to ~50Hz solo, disabling its self-powered thrice-stacked isobaric bass system to slip in the Submission instead worked like a charm. Here was my chance to compare low bass in stereo versus mono; and flat to equalized infrasonics. In hindsight the outcome was predictable. Stereo bass had a small advantage on image specificity or localization lock and also with the textures of acoustic instruments reaching low enough. Mono bass with 6dB/20Hz boost had the advantage on stage depth and venue 'realism' even if the latter meant entirely artificial constructs as built up by synths and carefully layered studio productions à la Mercan Dede or Hector Zazou. Since I love and listen to that type fare a lot—I call it organic ambient for its acoustic instruments embedded in modern synth ambiance—the Submission had my vote.

Folks who listen to a lot of blockbuster classical à la Mahler, Shostakovich, Strauß & Co. instead would probably prefer full stereo bass and happily forsake the extra output at the edge of audibility since their music stops sooner. What surprised me with the electrified Saadhana was the total lack of boom or undue corner pressurization. That was despite sitting more or less where all other speakers sit by necessity, just spaced a bit narrower to compensate for the straight-out orientation and as such a bit farther out of the corners. This suggested that the main issue with full-range speakers in that location really had been ported bass. What seemed to be room issues with ports which were tuned to between 20-30Hz were really speaker issues. I felt vindicated once more for disliking ported bass and thinking it improper at best. Back to the stereo/mono question. Mono coverage of 20-40Hz seemed unproblematic and quite uncompromised. That's certainly not what I'd say for the upper bass. Enter reader Michael Mills' email:

"Very much enjoyed reading the various installments in the Zu Submission review. I may be wrong but your comments represent the first positive endorsement of the subwoofer as a hifi genus that I can recall coming across in all my years of trawling through reviews in print and now online. Typically outside home theatre and car Audio magazines, the poor beasts seldom get more than faint praise of the 'well, I suppose if you must' variety. So very interesting to hear you firstly talking up the speaker+sub combination in principle and not just as a compromise or lesser of two evils; and secondly for stating the widespread suitability of a sub of this quality with many speakers, not just those from the house of Zu or those obviously lacking in bass. If I read you correctly, your positive comments are probably restricted to 'true' subwoofers that don't try to cover too great a frequency range. In that regard, how low do the main speakers need to be able to go by themselves to work well with a single Submission? Most of your review dealt with just filling in the bottom octave with speakers that are by themselves comfortable down to 50Hz but presumably with a different filter setting and more bass-challenged mains it could attempt to do more?"

Obviously subwoofers can be crossed in far higher than I did. My point for not doing so here was to avoid the otherwise very common issues of seams, fat midriffs, directionality issues, insufficient power-zone integration and more which have given subwoofers their deservedly bad rep. Once more, what's discussed here relies on a true subwoofer that hits a solid 20Hz; sports a finely adjustable low-pass filter that can be set to 20Hz or lower (none of these filters are sharp enough to be brickwall surgical); and speakers which don't require assistance save for roughly the first octave. Upper bass must not only happen in stereo but must emit from the same location as the upper bands. That's the main speakers. An 80Hz subwoofer low-pass would seem unworkably high to get the results I've enjoyed and described here.