Albert Von schweikert’s design goals for the UniField two, the middle model in VSA’s Studio Signature Series, were rather simple. Many of his customers asked for a small speaker that would work well in both small and large rooms with virtually any amplifier. Specific performance criteria were a large sweet spot, and enough bass output to simulate a larger floorstander. From a distance the UniField Two appears to be a two-driver system, and may well pass for a conventional stand-mounted two-way design. However, up close it is apparent that the upper 7-inch woofer is actually a coaxial design by SEAS of Norway with a 1-inch fabric dome tweeter nestled over the pole piece. So that would make the UniField a three-way design, right? Well, not exactly. The catch is that the upper woofer, featuring a PP/TPX polymer cone, is allowed to work into the deep bass while being augmented below about 80Hz by a 7-inch aluminum coned woofer. The end result is typically referred to a 2.5-way design, basically a two-way with a subwoofer. As Von Schweikert aptly points out, an important advantage of such a design is the elimination of the mid/woofer’s high-pass crossover network, and hence no capacitors in series with the critical midband. There has been much ado in recent years over the sound of capacitors with the cost of exotic types easily exceeding that of typical drivers. But it’s fair to say that the best-sounding capacitor is no capacitor at all. Instead of capacitive-coupling, the mid/woofer’s bass excursion is controlled by sealing it into a small internal chamber densely packed with Acousta-Stuf polyfill.
Coaxial drivers are rare birds in audiophile designs. Tannoy is justly famous for its dual-concentric driver and more recently KEF has made waves with its Uni-Q driver. A coaxial’s primary goal is to align the acoustic centers of the tweeter and midrange, “forcing” them to behave as a single driver so as to emulate the performance of a point source of sound. The payoff is vastly smoother off-axis performance relative to a conventional driver layout and thus a wider sweet spot. And as I’ll detail shortly, the SEAS coaxial is indeed capable of remarkable imaging due in great measure to its time-aligned wavelaunch. However, the practical engineering problem all along has always been the tweeter design, the traditional knock against coaxial tweeters being that they don’t measure very well. The fact that the coaxial tweeter is horn-loaded by the midrange-woofer cone makes it difficult to obtain a smooth frequency response. In fact, Von Schweikert considers the SEAS coaxial tweeter to be a bit of an enigma. He is well aware of its frequency-response imperfection, and that it lacks any type of fabric impregnation or fully pistonic motion, and yet despite all that, he finds it to sound wonderful. I was, at least initially, less enamored of this tweeter and can confirm that its on-axis frequency response is not particularly pretty due to a significant response dip in the lower treble and an excess of extreme treble.
On the matching factory stands, the speakers were at first toed in toward the listening seat, but I discovered rather quickly that I wasn’t happy listening to the tweeter head on. Since off-axis measurements showed a much more natural balance, I nixed the toe-in idea, pointing the cabinets straight ahead. This placed the tweeters at an angle of about 25-degrees relative to the listening seat and gave me the sort of balance I was after: a smoother lower treble partnered by a naturally rolled-off extreme treble. It should be noted that I’m not a fan of in-your-face treble and much prefer a middle of the hall presentation. With the speakers optimally set up, it became clear that the coaxial principle was working to perfection. Even without any toe-in, the resultant sweet spot was massive—no need to place your head in a vise to enjoy a stupendous stereo experience. When it came to imaging, the UniField delivered the goodies. I was most impressed by its exceptional focus and transparency, making it easy to resolve spatial outlines and subtle image shifts within the confines of a spacious soundstage. Resolution of massed voices was superb, allowing me to follow the ebb and flow of a particular voice in a chorus. After all of the preliminary experimentation, my view of the treble range crystallized sufficiently to pronounce it musical enough to enjoy, though it understandably lacked the transient finesse and purity of ribbons and electrostatic types.
The midrange driver turned out to be a winner, sounding smooth yet detailed, and manifesting a purity of tone which most cone mids would die for. The UniField dug into a complex mix with confidence. In particular, its resolution of artificial reverb launch and decay was scary good. Timbre fidelity was excellent even when scaling the full female soprano range. My only minor criticism had to do with slightly coarse upper-midrange textures, most obvious on violin overtones. This turns out to be the transition region between the midrange and tweeter, the crossover being at 2.2kHz.