As for the back panel, in addition to the binding posts there is a bass-level knob, a midbass level switch, the ARC in/out switch, the ARC set-up input (a mini-USB connector), and the ARC Setup Speaker Link (which requires an RJ-45 [Ethernet] connector), plus two status lights, one for the whole speaker, the other for the ARC equalization. The speaker-link connector, which ties the right and left arrays together, allows the ARC to program both speakers simultaneously. If you don’t have the requisite cable, all it means is the minor inconvenience of programming each speaker separately. The bass-level control is basically a tone control that operates below 75Hz while the midbass level boosts or cuts the bass 2dB at 200Hz. Both of these controls operate independently of ARC and regardless of setting are bypassed while ARC is in calibration mode.
With ARC on hand, you might wonder why these additional controls are there in the first place. Well, as noted, the Impression comes ARC-ready but not ARC-functional unless you purchase the optional microphone. These controls allow you a modicum of control over the mid-to-low bass and the upper bass apart from ARC. But even with ARC, these circuits come in handy for additional trimming and other fine-tuning of the bass, including compensating for bass characteristics of recordings, if you care to use them for that. For example, while the ARC does a very effective job of addressing room acoustics, a bass-shy recording—like a great number of my favorites by Szell and the Cleveland Orchestra—is still a bass-shy recording and will sound that way. The bass-level control is surprisingly effective for correcting this even after you’ve performed the room equalization. As for the 200Hz switch, again, many audiophiles like a lean upper bass which the Impression’s 2dB cut will help provide; at the same time, if you like more warmth in this area, then the 2dB boost will help, too.
Impression Bass with and without ARC
Let me say it up front: The Impression 11A with its built-in ARC engaged has provided the best bass response I’ve ever heard in my room in the areas of overall smoothness of response and of clarity, definition, and pitch differentiation. A few examples: One of my favorite recordings is the Sitkovetsky arrangement of Bach’s Goldberg Variations (Nonesuch) for string orchestra and harpsichord. There is only one double bass in the group, yet for the first time I heard it with a foundational definition that was rather revelatory. I don’t want to suggest that without ARC the bass is inaudible—far from it—only that with ARC you can follow the musical line with greater ease and a less effortful concentration, and there is a greater impression of air around it. The same holds for the one non-stringed instrument, the harpsichord, which is also separated out and easier to hear and to follow. In saying this, I don’t want to give the impression of anything unnatural or clinical in this clarity—rather, it’s just easier to listen into, as it were, yet at the same time allowing it to assume its rightful place in the overall texture without being submerged or calling undue attention to itself.
The same applies to another string orchestra arrangement—Bernstein’s recording of Beethoven’s Opus 131 string quartet with the full complement of the Vienna Philharmonic’s string section, including (where appropriate) the basses doubling the cellos. This is one of my desert-island discs. Played over these Impressions I didn’t hear details I’ve never heard before, but I was rewarded with clarity of line, texture, and articulation throughout the bass range that filled me with new respect for this inspired and inspiring performance and the way it is recorded. Another of my favorite recordings, Kei Koito’s organ recital of Bach [Claves] displays the same virtues of increased clarity and definition. The organ is a notoriously difficult instrument to record because it’s a difficult instrument in and of itself. Many churches tend toward a highly reverberant acoustical character that even in the best of hands militates against textural clarity. And truly full-range organ recordings that are recorded clearly can become muddy in systems that can’t handle the bass, especially when driven too hard.
This Claves organ recording is considered by Diapason magazine to be a textbook example of how to record the instrument optimally. The reason, I assume, is that it displays an ideal combination of clarity, articulation, reverberation, extension, and power—all of which (save only the last attribute) is pretty much what you get from the Impressions. And make no mistake; you certainly hear plenty enough power, especially in view of the relatively diminutive woofers. But that sense of ultimate room-filling bass power, plus crunch and slam—the kind I hear from my reference Harbeth Monitor 40.1—is “merely” excellent here without being truly outstanding. I believe this is because there is only so much you can get out of small drivers such as these eight-inch transducers, especially given the lack of any sort of baffle reinforcement. Having said that, however, I should add once you set aside these special categories of big music, only rarely throughout the evaluation period did I ever feel any serious shortcomings or limitation in the 11A’s bass response.
Fortunately, however, there is an easy remedy at hand for those who love the big stuff, though it comes at a cost: Add an REL subwoofer. Any number of good subwoofers will do the trick, but I favor the RELs because they are designed to be true sub-bass systems, that is, to add that last half-octave of bottom-end extension to speakers that already have excellent bass response. In that respect, MartinLogans, like full-range Harbeths, make ideal partners for RELs. The only potential drawback is that inasmuch as the RELs take the signal from the main amplifier’s speaker terminals, the ARC cannot operate upon the subwoofer. I didn’t find this a problem. For one thing, the bass acoustics of my room are very good and don’t present any oddities. For another, because the 11A’s bass response is already so extended, there is no need to set the crossover of the REL any higher than its lowest position. After that, get the phasing right and adjust the level, and you’ll be rewarded by some of the cleanest, most precise, articulate, and powerful bass you can buy. The difference is really audible on an awesomely spectacular recording like the Zander Mahler Sixth with the hammer blows in the last movement. By themselves the Impressions render these sensationally; with the RELs you feel them in the pit of your stomach.
Are there any downsides to ARC? Only one: As employed by MartinLogan, “all” ARC can do is make the bass response as accurate as possible in any given room. But this means that it will also “correct” characteristics you might find pleasing, such as a bit more warmth or power owing to standing waves or other modal effects. Objectively you will hear improvement, but your subjective response may evaluate it differently. I would have no problem living with the bass response of a un-ARC’d pair of carefully placed Impressions, but, though I do not consider myself a detail-over-everything audiophile, and the acoustics of my room are very attractive, I always preferred these speakers with ARC-corrected response.