The Zu Definition 2 Loudspeaker

There’s different for the sake of it, different for a reason and then there’s different with attitude. At first take it’s easy to place Zu Audio and their products firmly in the third category; after all, they do come from Utah. Not that there’s anything wrong with Utah, it just also happens to be the home of Wilson Audio, a pretty daunting neighbour if you happen to manufacture loudspeakers. But experience and a little sober reflection will soon have you revising that opinion. The Zu Definitions are distinctly different, but there’s plenty of cool, collected reasoning behind that difference.

Of course, even the paper spec tells you that this is no ordinary speaker. Zu’s claim of 101dB efficiency should attract your notice (although in around 95dB seems to be about right, calculated in the conventional way). But it’s the two large cones that decorate its upper half that standout, theoretically and visually. These are the same Zu260FR-G2 units that grace the company’s slim, monolithic looking Druid IV design reviewed by PM in Issue 45. Proprietary, high efficiency, wide bandwidth designs they are built onto a high-quality commercial basket and magnet assembly. But the paper cone(s), surround, voice-coil and central phase plug are all specified and assembled by Zu. Direct connected to the amplifier, without any form of crossover to get in the way, they form the heart of all Zu’s designs, running flat(ish) from around 40Hz to about 12kHz before finally tailing off. Of course, the trick with any such “single driver” design is to get as much bandwidth as you can without crippling the potential benefits when it comes to temporal and dynamic coherence and immediacy. Which is exactly where most of the real purists come unstuck. Push things too far and you end up with horrific frequency response aberrations and colouration to match. It seems strange to use the term conservative when it comes to Zu, but that’s exactly what these speakers are, in engineering terms at least.

Of course, 40Hz to 12k contains the vast majority of musical information, information that arrives via that single, directly driven driver. The result is a sense of tactile immediacy, an almost infectious impulse to conduct, sing and even dance along with the band. The undulating bass lines that underpin early Cure take on a living, breathing momentum, the slashing contrast of the sparse guitar riffs thrilling in their perfectly pitched and placed precision. They may seem slap dash and chaotic: the Definitions let you hear just how precisely the tracks are really crafted, but without robbing them of their essential pace and energy. This is what music is about; it’s what good hi-fi is about and it’s definitely what the Zu speakers are about. That they do it so successfully is down to the clever way in which the benefits of those broadband drivers are maximised and supported.

Nestled between those two large, paper cones there’s a tweeter, again the same as the one used in the Druid IV. It uses a composite phenolic resin cone/dome diaphragm, which Zu horn load with their own, turned aluminium lens. It’s rolled in using a single, high-quality Mundorf paper in oil cap in a first order arrangement, actually making the Zus conceptually closer to the Reference 3A speakers than anything else. In comparison they push the bandwidth of the main driver and the system efficiency, but the two brands share important sonic attributes as well as basic topology.

But the real surprise comes when you look round the back. The Druid’s shallow cabinet has been replaced by a large, square section enclosure built from 19mm ply, that stands bluff on its small plinth. The reason for the extra volume is the four, actively driven 10” bass drivers that fill the rear baffle. The cabinet is split at half height by a horizontal brace, the upper volume further divided front and back to create a midrange enclosure and two bass enclosures, each with a pair of drivers, but differing volumes. All four bass drivers are powered by a single, off the shelf, 120 Watt class AB amplifier, with a level control on the rear panel. They run from 16 to 24Hz where they start to roll off at 12dB/octave until 40Hz where the slope steepens to 24dB/Octave. However, additional terminals on the rear panel allow you to bypass the internal amp and filter, allowing you to use the same amp top and bottom, although you’ll need a separate filter/equaliser to do it. It’s an identical approach to Wilson’s passive WATCH Dog, with all the same potential benefits. Indeed, the WATCH Controller would serve perfectly, although Zu are working on their own external unit.

The review pair arrived in a special, pale satin finish, but the standard colours are bright red, black or blue gloss lacquers. This is one speaker that really does carry off the spectacularly beautiful Ferrari red! Internal wiring is Zu’s own (they made cables before they started on speakers and also give you a pair of their own mains leads), terminals are Cardas copper and all connections are cold crimped rather than soldered. You also get a comprehensive range of accessories (decent spikes and domed feet, cabinet and terminal cleaning kits and comprehensive instructions) to go with the superb finish. Zu even go to the lengths of listing the source of each element of the system, everything save the crossover caps and the amp module coming from the US. Yet this full-range, seriously engineered, beautifully constructed and finished, part-active, high-efficiency system will only cost you £8000 in the UK. Which makes it an awful lot of music for your money. How so? Zu supply their products direct to the end-user, and prefer their distributors to do likewise: hence the comprehensive set-up kit and instructions – and hence the low price. Thankfully, set-up is surprisingly straightforward, with a tendency to spread a little wider than most speakers. Toe-in is critical to correct staging, but it’s easily optimised and the biggest obstacle to achieving best performance is the two days or so the speakers take to settle down after being moved. That and just how clearly they revealed the temporary degradation induced by rearranging the Crystal cables!

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