December 2011

Zu Audio Omen Def Loudspeaker
The glories of prized cohesiveness.
Review By Dick Olsher

  Pronounced Zoo, not Z-U, Zu Audio is an American original proudly proclaiming to be a revolution in American hi-fi. The revolution has to do with craftsmanship and technology in the service of the musical experience. The star of the show is Zu's own made-in-the-USA 10-inch full range driver, which is supplemented above 10 kHz by a fill in tweeter. It's not the first speaker to market featuring a full-range driver, but only a select few models can claim to be almost entirely (90%) manufactured in the US. I applaud Zu Audio's commitment to twin-cone full-range drivers, a technology that originated in the 1930s. The twin cone had gained some measure of popularity in the 1950s and 60s, but seems to have been nudged out of main stream audio in the 1970s by the ubiquitous multi-way speaker.

The advent of three and four way designs with a multitude of woofers, squawkers, tweeters, and super tweeters, no doubt swayed popular thinking to equate more drivers with a higher-quality product. The inherent problem with multi-way speakers is that they slice and dice the audio signal with the hope that it can be reconstituted in the listening room. They are the sonic equivalent of the Veg-O-Matic. What are the chances of reconstituting a believable sonic image from a multitude of drivers arrayed on a baffle at various acoustic centers? Even a two-waywith a crossover around 3 kHz will struggle to integrate an image unless care is taken to time align the drivers. The problem is only magnified as the number of drivers increases. I'm not suggesting that it's impossible to do so, but most commercial multi-way systems I've auditioned over the years lacked one particular perceptual attribute; namely, cohesiveness.

Cohesiveness is not something that can be measured but can be easily perceived. It has to do with the perception of a loudspeaker speaking with a single voice. The avoidance of crossovers in the critical midband certainly helps, but full-range drivers are most convincing in this regard. I first heard the Omen Def during the 2011 THE Show in Las Vegas, and I liked it instantly. It sounded eminently listenable, lacking that infamous Lowther shout in the upper midrange, and seemed to perform quite well at the frequency extremes. The significance of its 98 dB sensitivity combined with a benign impedance magnitude wasn't lost on me. It appeared to be a potentially ideal load for low-power tube amps. The proof of the pudding was in the listening. At the Show it performed superbly partnered a 2-watt SET amplifier. Needless to say, considering its performance to cost ratio, the Omen Def made my short list of essential review projects for 2011.

A Few Technical Details
At a first glance the driver array on the front baffle appears to a D'Appolito configuration in the form of woofer-tweeter-woofer. Typically, the purpose of such a configuration is to improve vertical dispersion in the crossover region between woofer and tweeter. But here the woofers are in fact operated full range and roll off around 10 kHz mechanically without a crossover network. The cabinet height combined with a compact 12" x 12" foot print was suggestive of a transmission line loading, but that was not the case. A quick inspection of the front and rear baffles failed to reveal a bass reflex port and might lead one to conclude that this is a closed box design. However, if you're clever enough to check the cabinet bottom, you will notice a slot which provides the functionality of a port. It is essential to use the spike set bundled with the speaker to ensure that the speaker bottom is elevated about 3" of the floor. Failure to use the spike set would of course block the port and effectively convert the cabinet into a closed box. So the Omen Def is a ported design and measures like one with a box tuning frequency of about 42 Hz. The minimum impedance was 4.6 Ohm; no problems here for tube amplification. An impedance peak was noticeable at 4 kHz, which is indicative of cone breakup modes in this region.

Sonic Impressions
Chronologically, the Omen Def replaced the Volent VL2 SE in the reference system. Since the sound of Volent's superb twin ribbon tweeter as still fresh in my mind, it clearly highlighted the limitations of full-range twin cone technology. In the upper midrange where the woofer cone starts breaking up and the whizzer cone kicks in, the Zu sounded slightly untamed, adding some fuzz and grain to harmonic overtones. If you're into the Lowther sound, note that the Omen Def lacked the former's propensity toward primal screaming. And while that's a very good thing in my book, it actually strayed too far towards a darkish tonality. It sounded surprisingly polite and laid back through the upper mids and presence region. On the tweeter axis I measured a significant upper midrange recession centered at 3 kHz, no doubt due to interference effects between the woofers. It turned out that the magnitude of the recession was highly dependent on the mike's vertical position. The smoothest response was obtainable at about 2" below the tweeter. And that means that your best bet for a uniform frequency response at the listening seat is to place you ears slightly below the height of the tweeter. As a consequence some tonal colors were impacted. Soprano voice was reproduced with an harmonic structure darker than the real thing. In general, it would be fair to say that male voice was treated with greater deference than was female voice. There was plenty of upper treble directly in line with the tweeter axis, perhaps even a tad more than desirable. Experimenting with the toe-in angle proved essential in obtaining a satisfactory tonal balance at the listening seat.

OK, with the bad news out of the way, let's focus on the Omen Def's considerable sonic virtues. Its cohesiveness was responsible for an intrinsic capacity to craft a huge 3-D soundstage with an exceptional depth perspective. It excelled in terms of musical values. Its jump factor, the ability to unleash the music's dynamic range and emotional expressiveness was considerable. While low-level detail resolution was decent and at times even surprisingly good, this speaker was much more than just about the facts. For starters, rhythmic drive was admirable. But above all else there was on display superb interplay between musicians. The give and take between members of an ensemble was rendered to a degree I've rarely experienced with a multi-way speaker. Many speakers can resolve individual instruments in an ensemble, yet only a handful is capable of conveying an ensemble as a holistic and organic entity.

The Omen Def consistently generated a big tone balance at the listening seat. There was plenty of lower midrange,  upper bass, and mid bass energy to satisfy my sonic taste buds and do justice to the power range of an orchestra. Deep bass extension reached the low 40s in my room and bass lines were reasonably well controlled, though lacking in slam factor. Partnered with the 12 wpc single-ended Audion Sterling EL34 Anniversary integrated stereo tube amplifier, the sound was both warm and dimensional. The Audion emphasized musical over audiophile priorities and as such suited the Omen Def nicely. This sweetheart combo delivered warm and lush midrange textures. Single-ended amplification magic coupled with full-range drivers resulted in a depth perspective which at times appeared to push right through rear wall of my listening room. One generally associates imaging excellence with the minimonitor genre. But believe it or not, this large floor stander's imaging prowess is plenty competitive and it delivered the goodies with a tonal balance that minimonitors can only dream about.

Conclusions
Don't let the perfect be the enemy of the good. Every speaker introduces its unique set of compromises. Twin-cone full-range drivers necessarily concede some upper register smoothness and delicacy. But in return, the payoff is prized cohesiveness. Even with its flaws, the Omen Def does a very good job of capturing the fun aspects of music reproduction. For the record, I enjoyed my time with the Omen Def far more than I had with some speakers costing 10 times more. Packing a potent lower midrange and a big tone presentation it provides plenty of compensation for an upper midrange recession and a few rough edges. This speaker is all about being connected to the music, experiencing musician interplay as if at a live performance. It is less about being an observer and more about being a participant in the illusion of live. It deserves and shall receive my enthusiastic recommendation.

Specifications
Type: Two-way, three driver ported dynamic loudspeaker
Frequency Response: 30 Hz to 25kHz
Sensitivity: 98dB/W/m
Impedance: 6 Ohm nominal
Dynamic Range: 122dB
Crossover Frequency: 10 kHz
Dimensions: 12 x 12 x 47 (WxDxH in inches)
Weight: 78 lbs. each (net)
Price: $3,100 per pair

Company Information
Zu Audio
3350 S. 1500 W. 
Ogden, UT 84401

Voice: (801) 627-1040
Website: www.zuaudio.com