>>I am curious about the differences between Superfly and Definition speakers.<<
Having both Definition 2.0 and Druid 4-08 in two different systems, and having heard Soul Superfly at length, along with Essence and Presence, I can give you my view of the differences between Def 2 and Superfly:
Some background as I see it, from the standpoint of a customer who has followed the company closely. In some respects, all of the work Zu has done in single FRD speakers during the past three years has been directed toward narrowing the performance gap between Definition and everything else in their line. When I first bought Druids and Definitions over five years ago, the two speakers were seriously different in character though united by a common thread of coherence and phase linearity courtesy of the wideband FRD. But Druid at that time was a "dark" sounding speaker, a little beamy while Definition 1.X was explosive, open, and sparkled. The first step to narrowing the gap was, ironically, the release of Definition 2.0. It removed the primary disadvantage Definition had compared to Druid at the time -- the Def's sealed MDF cabinet produced resonant glare at high SPLs, whereas the Druid's open "partial Griewe" cabinet had far, far less MDF glare when pounded with current.
Then Druid 4-08 opened up the top end, smoothing out most of the known non-linearity to the high-frequency contour of the simpler Druid, and removed much of the sense of compression under high SPL that separated that speaker from Definition. There was less directionality in Druid 4-08 as well.
Essence, a speaker not fully realized in my view, did force Zu to resolve several lingering limits in particular elements of their speakers, which while not known for outcome at the time, made Soul possible. First, with Essence there was a clear objective to fully implement the Griewe model for managing the FRD's backwave while keeping to Zu's ideal "1 square foot of floor space" mantra. This was achieved, yielding flat response down to 30 Hz from a single FRD architecture. Then, a ribbon tweeter was incorporated to improve top-end dispersion, linearity, extension and apparent speed. This decision, in my view, was less successful, but it made the speaker appeal to a wider audience than Druid. However, regardless how you feel about the ribbon supertweeter, accommodating it led to a key Soul-enabling improvement. The FRD was revised (though it mostly looks the same) in the variables of cone mass, motor strength and high frequencies management via the phase plug. The cylindrical phase plug, especially the machining of its face, enabled a single FRD Zu speaker to bahve much more like the double FRD Definition in terms of horizontal dispersion and high-frequency linearity. Some of this benefit was obscured by having to dial back the FRD's efficiency to match the less efficient ribbon, but the stage was set for the next project.
The low price point objective for Soul forced more innovation and a serious holistic re-evaluation of how Zu builds speakers. To get under $2000 required detailed re-examination of labor and how it's used, the prime cost factor. Essence was a breakthrough in Griewe implementation but the boys had to find a cheaper way to do it if they wanted Essence bass performance out of a speaker costiing half as much. As a host of a Zu house party, I saw and heard some early prototypes for varying directions and where Zu ended up is a loooooooooong way from where they started.
Freed from the constraints of matching a ribbon and returning to the familiar dynamic lensed supertweeter let Zu take everything they learned from Essence refinements to the FRD and apply to Soul, without detuning the main driver. So the motor got stronger and the cone lighter, with the new phase plug incorporated. The Zu-standard 101db/w/m efficiency is restored. They conjured a way to not only get *better* Griewe performance than from Essence (same bass response from a smaller cabinet) but to do it in a more affordable but not compromised package.
The net result is that Soul Superfly, specifically, is the single-FRD Zu speaker that most narrows the performance gap with Definition. It's more dynamically explosive than Druid and presents more scaled soundstage when the music demands it. There's enough weight to the bass underpinning to obviate the need for a subwoofer and the spatial discontinuity resulting when you add more boxes. Superfly has more of the openness and top end reveal that Definition does so well, and horizontal dispersion is much more like Definitions, so it doubles as an excellent home theater speaker better than Druid, in broad rooms with scattered seating. The overal octave-to-octive tonal balance is far closer to Definition's neutrality than was Druid at the start, and audibly better than Druid 4-08. Yet, Soul retains Druid's advantage over Definition in near-field listening and small-performance ultra-coherence courtesy of having only one FRD. The inimitable directness of Druid is fully retained for intimate listening while resolution pushes up the scale closing perhaps 40% of the former detail gap between Druid 4-08 and Definition 2.0.
Now, this won't last. Definition 2.0 is still easily worth its greater cost. And that cost multiple over Soul Superfly will make more people choose to settle with the simpler, smaller, lighter speaker. Another friend of mine here in Los Angeles took delivery of a custom-ordered pair of Definition 2.0 with the Soul-type FRDs. This is the only pair in the field with this configuration, AFAIK. They widen the gap and are better than my early Def 2s. The overall advantage of scale, ease, linearity and explosive dynamic rise intrinsic to the dual FRD Definition architecture fully inherits the advantages of the Superfly-style FRD, and so it goes. Plus, Definition will be redesigned completely, eventually.
Soul Superfly will never catch Zu's best but it is more than good enough to make the point that if you hypothetically can afford a system at the cost of Definitions + $2,000, a pair of Superfly on the right $10,000 of amplification will yield a more convincing stereo than a pair of Definition 2s powered by good $2,000 amplification. Move the spending scale for amps into the $3500 - $5,000 range paired with Definitions and the advantage moves to Defs plus, however.
Soul Superfly is game changer in how you allocate resources to a system and assemble it. It isn't a Definition but you can consider it a "Definition-enabled" Druid. At least until Zu figures out what to do in the middle of the line.
Does that answer your question? If not, ask for what's missing.
Phil
