Bookshelf Speakers

Zu Audio Druid Mk 4/08 Speakers

Zu Audio Druid Mk 4/08 Speakers


High sensitivity speakers have had a following amongst the proponents of low power single ended tube amplifiers for a long time. Many of these speakers work well with these low power amps, but not necessarily with more typical amplification. Not so with these Zu audio Druids. While I am sure they still are wonderful with low power tube amps, they also deliver with more typical solid-state amplification. The Druid, made by cable and speaker manufacturer Zu Audio in Ogden, Utah, has had a cult following among many audiophiles. I was able to test the latest Mk. 4/08 version, released earlier this year.


  • Design: Sealed Enclosure, Two Drivers, No Crossover
  • Drivers: One 1" Dome Tweeter, One 10.3" Full-range Driver
  • MFR: 35 Hz - 30 kHz
  • Maximum Power: 300 Watts RMS
  • Efficiency: 101 dB/W/M
  • Nominal Impedance: 12 Ohms
  • Dimensions: 50" H x 11" W x 6.3" D
  • Weight: 60 Pounds/Each
  • MSRP: $3,400/Pair USA
  • Zu Audio

The Design

Zu uses a proprietary acoustical modeling technique, called ZuRG , to design their speakers. The Druid is equipped with Zu-manufactured and designed drivers, including a wideband 10" driver and a composite dome super tweeter with machined aluminum horn radiator. The wideband driver covers 35 Hz to 12 kHz. The super-tweeter covers only 12 kHz and up. The wideband driver is crossoverless, while the supertweeter uses a simple high pass network. Like my Gallo Reference 3.1's, crossovers and their accompanying phase and time domain errors, are kept to a minimum. The cabinet is ported on the bottom, so the speaker's height above the floor (set by the feet) is relatively important. The cabinet porting is neither an acoustical waveguide nor a traditional port, and is one of the tricks of the ZuRG modeling. Impedance is a very easy to drive 12 Ohms, with an extremely high sensitivity of 101 dB per Watt per meter.

Internal wiring is Zu-made silver alloy B3 wire. The cabinet is MDF core wrapped in a composite skin. Combined with automotive paint, in standard or custom colors, the finish is just about perfect. Sean Casey of Zu apologized, saying the speakers had been used many times as a demo pair, leaving the finish less than perfect. I don't know what he was talking about. The Druids were the best-finished loudspeaker I have ever reviewed, and are up there with the best finished I have ever seen. Mine were finished in a rich, attention getting red, with a silver base and Zu logo. The binding posts were also the best I have ever had the pleasure of using. These patented Cardas binding posts have OFHC copper pins are mounted in a high quality plastic housing. A clamp, secured with a single large wheel holds the spades against the copper pins. These are really optimized for spades. Other terminations can be used, but they need to be kludged in a bit. Every part of the Zu speakers, from the cabinet finish to the binding posts to the drivers exuded quality. It is clear just from looking at them that the $3,400 asking price is a great deal. Three non-standard paint colors run an extra $600, and a black anodized tweeter, driver trim or phase plug run a few extra dollars each. If you want Zu to paint to any custom color, they will, but pricing is provided on demand.

Zu Audio Druid Mk 4/08 Tweeter

Speaker mass is a moderate 65 lbs. The only design element I could find to poke at a bit was some cabinet resonance. Tapping on the front or rear baffle did result in a bit more ringing that you might expect. While the cabinet might be plenty stiff, it was not particularly inert. Some manufacturers use the flexibility of the cabinet as a part of the acoustical suspension of the drivers, so I have no idea if the "liveness" of the cabinet helps or hinders the performance. Really it's irrelevant as long as the speakers deliver the sonic goods.

Zu Audio Druid Mk 4/08 Speakers Rear Panel


The Druids came packaged one per box, with high quality foam packaging. Each speaker came with both spikes and hard floor feet, and a micro-fiber polishing cloth. The speakers come coated with a thick layer of automotive wax, which has to be buffed off by the user. This guarantees the highest quality finish, but does require 15-20 minutes of elbow grease per speaker. The result is well worth the effort!

What the buffing does cost in effort, Zu gives back many times over in break-in time. Each speaker is broken-in at the factory for 160 hours (almost a full week, 24 hours a day) using a Zu-developed technique. This means the speakers are ready to go right out of the box. No need for weeks of break-in, and wondering of you made a huge mistake waiting for the speakers to begin to perform.

I located the Druids in my room approximately where my Gallo 3.1's live. My room, as a day-to-day family room, has limitations that prevent me from placing speakers anywhere. I have little issue with this, as very, very few audiophiles have the luxury of a single purpose listening room they can set up in an arbitrary way. I toed in the speakers directly at the listener as recommended by Zu. The speakers were powered by my 200 WPC Emotiva RPA-1 amplifier using Wireworld Eclipse speaker cable with spade terminations. Zu recommends using a CD case to set the cabinet to carpet gap, which I did.

The Sound

Given the extensive factory break-in (and the fact these speakers have been played before) I was able to begin listening immediately. Very seldom do the first few seconds of listening to a new component leave me open mouthed. The aliveness and realism of the Druids are nothing short of amazing, and exceed any loudspeaker I have ever heard. High sensitivity loudspeakers are known for spectacular dynamics, which make the music sound "alive," but the Druids deliver this quality turned up to eleven. The Druids have the expected macrodynamics that provide punch and drive, but even more important to the realistic presentation of the musical event are the microdynamics. The subtle changes in loudness from moment to moment are, in my opinion, the key to delivering realistic sound. Not timbre, or frequency extension or soundstaging, but dynamics. The wide dynamic range of the Druids allowed them to play very loud with no audible compression or confusion. Not to the same level as the megabuck Triad Platinums I listened to a while ago, but still plenty loud, and with very little drive power required. My normal Gallo Reference 3.1s sounded relatively flat and two-dimensional by comparison. In addition, the collection of unique sounds presented in the soundstage by the Druids were tonally and dynamically smoothed together by the Gallos.

This superior dynamic presentation was most noticeable in the midrange, and was likely due to the Zu audio wideband crossoverless driver. Adding to the wideband driver's performance was the crystal clear supertweeter. While the top end did not seem as extended as that of the Gallos, the smoothness and precision delivered by the Druid top end won the day. As in the midrange, the Druids were able to separate and reveal the details of instruments in the soundstage without any blending. When compared to the Gallos on the same recording, the Druids were able to pull into focus sounds that were there with the Gallos, but blended into the surroundings. It's not that the Druids made the sound compartmentalized, either. Everything sounded perfectly natural and realistic, just with more resolution.

Soundstaging was a wash, or just a bit behind the Gallos. The Reference 3.1s throw a soundstage in my room significantly wider than the speakers, with no sign at all that the speakers are there. The Druids also were able to disappear, but the soundstage was more severely truncated at the loudspeaker. This was likely a result of the strong toe-in, but this was necessary to maintain imaging performance. The Gallo tweeter has a particularly wide power pattern of 120 degrees, compared with the Zu tweeter's 30-degree power pattern, allowing for a strong central image with no toe-in. The Druid soundstage was behind the plane of the speakers, which gives a sense of a much larger soundstage. This is particularly desirable if you listen in a small room. In addition, the tall Druid cabinets with top mounded wideband driver present a very tall soundstage, particularly when compared to the short Gallos.

Bass performance was excellent for a speaker with a limited low end. The bass was excellent down to the last octave, with the wide dynamic range and dynamic performance providing plenty of punch. Tonality was also very good, with the aliveness of the midrange continuing down to the low end (where, admittedly it does not matter as much). The bottom octave was simply gone, as it should be with a limited low end. This is where the Gallos really were superior to the Druids. The Gallos, with their second voice coil driven, go all the way down to about 25 Hz in my room with no roll-off, and are only a few dB down at 20 Hz. The extra power and oomph delivered here is particularly noticeable on the electronic music I listen to so much. My new (but old) favorite, Fluke's 1997 release Risotto, really craves that last octave. It sounded wonderful on the Druids, but really did not deliver without the bass.

Other genres were not so challenged. Particularly on acoustic jazz, like Miles Davis' Kind of Blue, the Druids kicked the Gallos all over the listening room. When that last octave didn't play a big role, the sheer aliveness of the Druids recreated something that sounded more real and visceral that anything else I've heard in my room. Even with the spatially narrower soundstage, the realness was unmatched.

The only complaint I had was a small midrange timbre issue, at least to my ears. Some midrange sounds near 500 Hz or so sounded a little fuzzy. At first I thought this was due to a cabinet resonance, but that would also tend to blend and confuse the sound in that spectral region. I heard none of this, but the individual instruments were a bit more warm and round than I was expecting. Timbre is one of the most individual and subjective qualities of a loudspeaker, so I can't really say that what I heard was any more right or wrong than anything else, but I call them as I hear them. Your interpretation may very well be different.

On the Bench

I used a Smith and Larson Woofer Tester to measure the Druid's impedance as a function of frequency. The results are shown in two ways in the plots: the traditional amplitude and phase plots, and the smith chart plot I wrote about several months ago. Impedance stays at 8 ohms or higher for the entire audio band, with large phase angle deviations seen only at low frequencies. These magnitude and phase angle excursions are due to the port tuning of the loudspeaker enclosure. Phase angle rises gently in the treble. Looking at these results on the Smith chart, normalized to 16 ohms, the impedance trace stays nicely near the center of the plot, more or less within my arbitrary +/- 50% impedance circle. Most of frequency space is well within the circle. The endpoint near the center is 20 kHz, and the marker cross is at 1 kHz. Most of the data slightly outside the circle is at low frequencies, and occupies a small range of frequencies. This makes the Druid a relatively easy loudspeaker to drive, with high average impedance throughout the audio band, and no weird reactive impedance deviations.

Zu Audio Druid Speakers Test Results

Zu Audio Druid Mk 4/08 Speakers Test Results

I also measured frequency response for the first time with any of my reviews. I used a calibrated Earthworks M30BX microphone with a Roland Eridol UA-101 24 bit 96 kHz USB soundcard and SpectraPlus FFT analysis software. John Johnson, the editor of Secrets, provided a calibration file for SpectraPlus. Absolute calibration was done with a Radio Shack SPL meter. The microphone was mounted on a boom stand on axis with the tweeter, and placed about 1 meter away (after calibration).

The results of playing a 0 dB full-scale white noise signal are shown here. I would completely ignore all frequencies below 200 Hz in detail. All the structure you see, save the roll off at 40 Hz, is due to my room. My room is terrible in the bass. I had to control huge resonances with bass absorbers, which have made the corresponding suckouts worse. The general trend of a gentle roll off below 100 Hz towards 40 Hz, with a more aggressive roll-off after that is the main point. Midrange and treble performance is rather flat, with a bit of a dip at around 12 kHz, at the crossover frequency between the wideband driver and supertweeter. As I can't have the microphone on axis witht the wideband and supertweeter simultaneously, I would guess that this is also a measurement effect. Again, most of the small scale structure is due to room interaction. If I had an anechoic chamber, the response would be smoothed out quite a bit, but I don't.

Zu Audio Druid Mk 4/08 Speakers Frequency Response

As this is my first try at loudspeaker measurement, these results may be replaced with better, and possibly additional measurements in the next week or two.

Conclusions About the Zu Audio Druid Speakers

If you don't crave that bottom octave, I can't think of a better way to spend $3400 on a full range loudspeaker. Your money buys you a spectacularly well-finished loudspeaker made entirely in the USA, with custom, in-house manufactured drivers. The realism of the musical event these speakers can deliver is unmatched by anything I have ever heard, and that can be directly connected to the very high sensitivity and dynamic range of the Druids. As we all well know, bass is expensive. Zu will happily sell you a speaker that delivers that last octave without sacrificing any of the Druid's magic, but the price of admission is more than double that of the Druid. In the end, I liked my Gallos wider soundstage and low range extension and power too much to give them up. Now maybe if Zu offers a pair of Presence or Definitions to review ($8000 and $11000 respectively), things might be different. However, this is a decision mainly based on my love of electronica. If my musical tastes did not include this genre, I guarantee my decision would have been different.