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 November 1, 2007  A Method to the Madness: Zu
Audio Method Subwoofer
They’ve answered the first question brilliantly with the Zu Druid loudspeaker ($3400 USD per pair), which has lately been showing up in recording studios. The reason: real dynamic range. The Druid has claimed 101dB efficiency, is rated to play to 125dB in a room, has low frequencies that extend below the lowest note of a standup bass, and has the coherence of full-range drivers. I corresponded with the owner of a recording studio who’d replaced his very-high-end monitors, made by the British firm PMC, with Zu Druids because his clients could feel the music’s impact through the Druids, whether a softly plucked guitar string or a slamming bass drum. He loved the fact that a single driver could reproduce 98% of the music, augmented by only a single supertweeter, for the ultra-high-frequency response. No 6dB crossover is needed to try to emulate point-source coherence. The Druid is a point source. But the Druid peters out below 35Hz. So what's a Zu to do? They needed a subwoofer. First and foremost, any Zu sub would have to have the dynamic range of the Druid; in other words, it would have to have ultrafast response. Second, it would have to offer real performance at all of the frequencies real music lovers listen to. I’m not talking about hi-fi geeks who carry around obscure recordings of Danish jazzbos that have been recorded with the microphones placed only centimeters away from the instruments. I’m talking about the dynamics and low frequencies of music that most people listen to, such as Pink Floyd and Miles Davis and Kanye West and Linkin Park. Third, any Zu sub should be able to play as loud as the Druid, and that’s really loud. Finally, a Zu sub should move lots of air. Bass thwacks should compress the air in a room until the moving air can be felt; the impact should hit you in the chest. With those design goals in mind, Zu came up with the Method subwoofer ($2500). It’s not a conventional little 12" cube. While some of those Sunfire clones have made impressive bass, most won’t play loud enough to keep up with the Druid. Plus, I’m always a little concerned about using a very-long-throw driver to make a small cone move more air. The delicate dance of rubbery surround, cone stiffness, and incredible magnetic power is difficult to pull off. I own a Sunfire sub, and I’ve seen the thing dance all over the floor in reaction to deep bass. Think of the pressure on the cabinet and driver that would allow bass notes to move a 60-pound box. Plus, how does a cone with a pistonic excursion, or stroke, of 2.35" respond to the source’s request for a note that requires 80 oscillations in a single second? Another possibility was for Zu to use the subwoofer section of their top speaker, the Zu Definition: four 10" drivers that together reach well down into the 10-20Hz range. But that would make a standalone subwoofer more than 4’ tall. For the Method, Zu ended up going with a common-sense design that harked back to the old days of subwooferdom: two 15" drivers moving a lot of air. The single 10" circular driver found in the typical compact sub has a surface area of 78.54 square inches. The Method’s two 15" cones have a total area of 353.43 square inches. That’s 4.5 times the amount of area with which the cone can push air. The 10" cone has that long stroke, but is that really a benefit? The most optimistic numbers for a 10" driver with a 2.35" stroke show an equivalent of 235 square inches of air-pushing area, which is still nowhere near what the Zu has. And since the Zu cones don’t need such a long stroke, they can recover more quickly. Nimble bass. An agile bass driver is a good thing, but to mate up with the Druid, the Method also needed bass extension and volume. The specs tell only part of the story, and Zu doesn’t even offer a loudness specification. And their frequency-response claim of 20-200Hz speaks only of bandwidth, not tolerances. This is actually a promotion of the consumer’s interests: the performance of any sub depends on the room it’s placed in. To test the Method by itself, I placed it in the position currently owned by my Sunfire Signature sub, between my ATC SCM50 speakers. The ATCs will put out 112dB all day long and are happy pumping out frequencies down to 38Hz, but below that there’s almost nothing going on; the Method seemed the perfect partner. As usual, when I set up anything new, my wife offers her 2¢ on the looks. She loved the Method’s retro looks and high-quality finish. I was wondering how the hell Zu fits two 15" drivers and an amplifier in a box measuring only 32.3"H x 17.3"W x 12.6"D. For anyone who’s set up a sub before, the Method should be a snap. I began by setting the crossover point at its lower limit of 40Hz, the phase at zero, and the output level at noon. Oops. The Method’s one oddity is that, because it’s designed to partner a 101dB-efficient speaker, its volume control gets loud early and fast. If you dial the output to what seems a normal setting, as I did, you’ll be blown out of the room. Try 9 o’clock. A little more work with the level control and my RadioShack sound-level meter and I was ready to roll. When reviewing subs, I always start with "So What," from Miles Davis’ Kind of Blue [Six Eye LP, Columbia 8163 and Sony SACD M64935]. Chambers’ bass has a woody, real-room character that immediately shows up bass anomalies. The outputs of the Method and my ATC speakers blended without any glitches or discontinuities. The opening track of the Mission: Impossible soundtrack [CD, Polygram 454525] has deep percussion, low synthesizer bass, and huge dynamic range. The Method sounded effortless and clean. How important is clean in the bass? Many subs, especially the little cubes, put out distortion levels as high as 10% when driven to normal levels. Many say you can’t hear the distortion at low frequencies, but given the choice of distorted or undistorted bass, I’ll take the latter. So the Method worked perfectly with music. Next, I inserted it into my home-theater system and used the Blu-ray edition of 300 to check its abilities with big bangs. The air-conditioner intakes rattled -- no other sub has ever accomplished that -- and the environmental rumblings (great Foley in this movie) sounded authentic. The sounds from TV shows also came through beautifully. Whoever’s doing the sound design for Shark obviously digs low frequencies; it was such a pleasure to hear them undistorted and uncompressed. That was one of the reasons I love the Method. As with a massive Anthem or Krell amp, I felt as if zero strain was being placed on my system, no matter what I threw at it. The other object of my affection was the Method’s sprightly responsiveness. The ATCs are used in studios around the world because they’re quick, revealing, and accurate. Most subs I’ve tried make my system sound as if a sub has been added to it. The Method seemed to contribute no "sound" of its own; instead, the ATCs seemed to have suddenly gained 20Hz of bass extension. A few months ago, I reviewed JL Audio’s Fathom f112 subwoofer. At the time, it was the best sub I’d ever had in my system. Part of the reason for its success was JLA’s brilliantly implemented Automatic Room Optimization (ARO) software. My room has a 45Hz resonance, and I’m not alone in having such a problem. Unless a very pricey audio engineer with an unlimited budget designed and built your listening room, you’ve got resonance problems, too. In my room, in order to keep that main resonance under control, I have to keep the level of most subs lower than I’d like, which prevents me from getting the full impact at 20Hz. The Fathom f112’s ARO tamed the 45Hz resonance; I could then boost the other frequencies and get the full impact from the bottom octave. The Zu doesn’t have ARO, so by itself, it would have trouble competing with the JLA. Integra to the rescue. Their newest home-theater processor, the DTC-9.8, includes the smart Audyssey system, which does an even better job of taming room resonances than JLA’s ARO. Thus I had a level playing field on which to compare two subs that are quite close in price: the JLA costs $2700, the Zu $2500. In terms of sheer oomph, there was little to choose between them. The JLA has only a 12" woofer (for a cone area of 113.1 square inches) but a whopping 3" excursion. Both subs were almost perfectly accurate, but there were differences. Think of the JLA as a Hummer H-1 Alpha and the Zu as a Dodge Viper. Each passed every torture test I could throw at it, but the Zu felt a bit more responsive to the trailing sounds of bass instruments in natural spaces, such as the bass drum in Orff’s Carmina burana [CD, Telarc 80056] The JLA felt a bit more authoritative in the explosions in Resistance: Fall of Man. In any case, the differences were subtle. Both could play loud enough to fill a club with block-rockin’ beats. In a few areas, the subs were very different. First, the JLA’s 2000W amp drew a whopping amount of current from the wall. It’s not alone in that -- most large-excursion cubes do the same. The Zu’s 120W amp was much more abstemious in its appetite for power. The drivers, too, are different. JLA, who made their name producing some of the best car subs made, already make their drive-units in house. Zu buys its drivers from Eminence, who make speakers for Marshall and Fender guitar amps, and Ampeg and Gallien-Krueger bass amps. The subs look very different: The JLA’s piano-black finish looks very rich, and its controls are on the front; the Zu looks retro, with controls on the back. Then there’s customer service. Every time I called Zu, I got someone on the phone who knew the answer to my question, who seemed to care that I was happy, and who clearly loved what he was doing. I didn’t have such luck at JLA.
But the biggest difference is in the design. Which makes more sense? A small driver with a large excursion, or a large driver with limited excursion? If I were buying, I’d probably go for the Zu, for two reasons. First, I’m a believer in huge voice coils, massive magnets, and short excursions. That’s the philosophy at ATC and Thiel, makers of my current and past reference speakers. I think that control shows up in the delicate places between notes that make the music come alive within a three-dimensional soundstage. While I think it’s less important in a subwoofer, it still matters. Second, Zu feels like a company I want to support. They’re music lovers. They’re friendly. They’re enthusiastic. In fact, I never felt as if I was being sold a product. I felt they were friends sharing something they were really excited about. Need proof? For the Method, Zu offers a 60-day, no-questions-asked return policy, and they throw in one of their 2m Birth power cables ($149) for free. The only downside to the Zu is that you’ll have to find another way to tame your room’s resonances. The problem is big but surmountable. I believe we’ll shortly be seeing a slew of new products that include the Audyssey system, which does a better job of taming resonances than anything else I’ve tried. But even if you want to keep the amplification you’ve got, there’s always the Velodyne SMS-1 ($599 from Outlaw Audio). Of course, by the time you’ve spent that much money, you could step up to the JL Audio Fathom f113, Home Theater & Sound’s 2006 Product of the Year. Choices, choices. At least you’ve got options. The Zu Method delighted me. It has more than just bombast. Its clarity, resolving power, and ability to "disappear" into the music make it a very rare creature: a subwoofer that honors music as much as movies. Very highly recommended. …Wes Marshall Zu Audio Method Subwoofer Zu Audio Website: www.zuaudio.com
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