Description and Design
As horn fans are wont to point out, the first loudspeaker (Emile Berliner's) was a horn, and horns have an inherent advantage over any other type of loudspeaker in their ability to produce the most sound with the least electrical input. Horn critics counter that while efficiency was important when amplifier outputs were restricted to the 2-5W range, high efficiency is no longer required now that much more powerful amplifiers are available, and that horns' high efficiency comes at the price of colorations (frequency-response and phase anomalies) that detract from the accuracy of reproduction.

Avantgarde's response to these criticisms is that, regardless of available power, horns' high efficiency confers benefits in dynamics and low distortion, and that careful design can reduce horn colorations to a negligible level. The Avantgarde speakers feature a spherical horn construction, which is said to yield exceptional uniformity and integration of the response in the vertical and horizontal planes. The horn is made of ABS, a material chosen for its neutral resonance behavior, resistance to temperature- and humidity-induced changes, and because it can be manufactured to close tolerances—all factors that are critical to performance. The only downside is that the manufacturing process is quite expensive.

The Avantgarde Uno is technically a hybrid: a sealed-box cone subwoofer supplements the horn-loaded midrange and tweeter modules. The midrange driver is a 4" unit with a 2.5" dome, covering the range from 220Hz to 3500Hz, and was developed especially for the Uno. In the original Uno, the tweeter's sensitivity was lower than that of the midrange, which required a network to lower the midrange sensitivity by 1.5dB.

The Uno Series Two has a new tweeter that matches the midrange in sensitivity, so that the midrange is now driven directly by the amplifier, with no electrical crossover. The midrange driver's physical design produces an acoustical rolloff of 12dB/octave above 3.5kHz and 18dB/octave below 220Hz. The tweeter's response potentially extends down to 1kHz, but it's rolled-off by a 12dB/octave crossover at 3.5kHz so that it matches the midrange. The crossover uses high-quality polypropylene-foil capacitors, air coils, and metal-oxide resistors. The tweeter has an oversized 6.5-lb magnet, and its claimed power-handling capacity is more than 100W.

The new SUB225 CTRL PRO subwoofer, optional with the Uno Series Two (the speaker is also available with the 217 PRO subwoofer, at a $1000 saving, but Jim Smith strongly recommends the 225 CTRL PRO), represents a major design effort to have a subwoofer that matches the horn drivers in efficiency and sonic character. The two 10" subwoofer drivers are apparently quite special: 3" voice-coils, 15-lb high-energy magnets (BL-force factor of more than 19 newtons per ampere, if that means anything to you), 0.71" excursion, each driver with a power-handling capacity of 250W (RMS), and a sensitivity of 95.0dB. The subwoofer drivers are connected in parallel, yielding an efficiency of over 100dB, thus matching the horns' efficiency. The enclosure is of 1.2"-thick MDF, with very rigid construction.

Integrated with the rear panel of each subwoofer is the PA101 power amplifier/crossover. The amplifier puts out 200W and is optimized for bass reproduction, with a high damping factor to control the drivers. The PA101 also features what Avantgarde refers to as a velocity-controlled driver feedback system. This is not a conventional servo control using an acceleration sensor on the driver, but a type of equalization that varies with changes in signal level and frequency.

The final step in the production of each 225 CTRL PRO is the tweaking of the driver control circuit, taking into account variations in the characteristics of the specific drivers. User controls include potentiometers for subwoofer level and crossover frequency (variable from 90 to 220Hz, 12dB/octave), and a switch that allows selection of 20, 25, or 30Hz as the low-frequency extension point (12dB/octave), with an additional constant 6dB/octave filter at 18Hz to protect the system from damage. I'll take bass quality over quantity any time, so I used the 20Hz setting. The PA101 takes the signal from the amplifier speaker output rather than the preamplifier, which is said to preserve the main amplifier's tonal and dynamic characteristics, enhancing the integration of the subwoofer with the rest of the range. (REL subwoofers use the same approach.) The subwoofer amplifier presents a high impedance load, so driving it draws a negligible amount of power from the main amplifier.

When it comes to describing the Uno's appearance, I'll forgo taking up a thousand words and leave the task to the photo accompanying this review. Although the Uno is the smallest Avantgarde, it's still a pretty big speaker that takes up a considerable amount of floor space, and it's not exactly visually unobtrusive. I find the form-follows-function honesty of its industrial design quite appealing; the Uno looks like a speaker, not a speaker masquerading as a piece of French Provincial furniture.

The finish on the review sample was the standard white polished ABS, with the subwoofers in gray Nextel. The speaker is also available with the horns and sub in matching automotive metallic lacquer finishes, which boosts the price by as much as $2000—a bit steep, if you ask me. I quite like the standard white ABS—even if the midrange horn does bear a certain resemblance to a Yamaha Sousaphone. The quality of fit'n'finish is exceptional, confirming Avantgarde's claim that their products have much in common with Porsche, Leica, Mercedes-Benz, and other examples of German craftsmanship.

Setup
Given the Uno's size and unusual dimensions, unpacking and setting up a pair of them was not as much of a chore as I had anticipated—once I figured out that the midrange and tweeter have to be switched around from the way they're shipped, a fact the instructions fail to point out. The speaker consists of three parts: midrange horn, tweeter horn, and subwoofer, which are all attached by long bolts to three metal posts. There are three sets of holes in the posts, allowing the horns to be mounted at different levels depending on the height of the listening seat. The highest mounting position is recommended unless the listening seat is very low, and this worked well in my situation. As delivered, the weight of the entire speaker, including the subwoofer, is supported by the posts, which have feet that allow the speaker to be moved around with relatively little difficulty.

Once the speakers are optimally positioned, a set of four supplied spikes can be screwed into the bottom of each subwoofer, and the posts' feet removed, which gives the speaker more solid support. I followed this procedure, and found that the installation of spikes improved general focus and tightened the bass. The Uno can be single-, bi-, or tri-wired; short pieces of cable are supplied for joining the different modules if single- or biwiring is used. For all my serious listening, I used Nordost SPM biwire speaker cable, one pair connected to the midrange and the other to the tweeter, with the supplied Avantgarde wire linking the midrange and the subwoofer.

I initially set up the Unos in the living room, just to give them some playing time until the arrival of Jim Smith, who had offered to come by for a visit to help carry the speakers upstairs to my listening room and check that they were working properly. The Uno is heavy (the subwoofer alone weighs 100 lbs) and awkward to get ahold of, so taking them up the narrow set of stairs to my listening room involved a certain amount of weeping, wailing, and gnashing of teeth.

Once in the listening room, they were placed in what is my more-or-less-standard position, along the long side of my 16' by 14' by 7.5' room, forming an angle of about 70 degrees from the listening position, toed-in to point almost exactly at the listening seat. The distance from the listening position to the midrange driver (the driver itself, not the front of the horn) was about 9.5'.

Jim Smith had brought along a 1/3-octave spectrum analyzer, which was useful in tweaking the subwoofer levels. My room has a closet with louvered doors on one side, which tends to create a L/R bass imbalance; the Uno's subwoofer's level and frequency controls were able to correct this to a considerable extent. Subwoofer phase is reversible by the simple expedient of reversing the subwoofer cable connections; I left the sub in phase with the midrange and tweeter. The horns' controlled dispersion (narrower than that of direct radiators) is supposed to make them less sensitive to room acoustics; this may be so, but a pair of RoomLenses placed to the outside of each speaker still resulted in a reduction of "room sound" and a wider soundstage.

The Uno's powered subwoofer allows the use of main amplifiers with much lower power; unfortunately, it also means that there are two more amplifiers in the system, with greater opportunity for ground loops. And, sure enough, when I first set up the speakers in my listening room, I got all sorts of buzzing and humming noises coming through the midrange horns and the subwoofers. In my experience, the only way to solve ground-related noise problems is to try different grounding and hookup arrangements (each piece of equipment grounded/ungrounded; preamp, power amp, and subwoofer amp plugged into the same outlet/different outlets) and hope that some combination works. The Uno's sensitivity is about 13-15dB higher than that of the average audiophile speaker (footnote 1), which means that noise as well as signal will be correspondingly higher. In any case, I was able to get ground-related noise down to an acceptably low level by grounding some of the equipment and letting the rest float.

Sound
One of the most thought-provoking articles to have appeared in Stereophile in recent years was Markus Sauer's "God Is In the Nuances" (Vol.23 Nos.1 and 2). Taking another run at the perennial problem of defining what it is exactly that we want from a music-reproduction system, Markus argued that the main reason people listen to music is to have an emotional experience. He presented experimental evidence (from a doctoral thesis by Jürgen Ackermann) to show that some audio components are markedly superior in their ability to produce an emotional response in the listener, and that this emotional response is a function of subtle factors in the reproduced music, factors that are difficult to identify by the sort of critical analysis normally performed by audiophiles and reviewers.

Markus' example was of the superiority of an analog/tube system over a digital/solid-state one in producing an emotional response to the music, but he might well have been talking about the Avantgarde Uno. There was something utterly compelling about this speaker's presentation of music, something that produced an emotional response in a way that rendered almost pointless the analysis of sonic attributes commonly used by audiophiles and audio reviewers. The Uno drew me into the music, focusing my attention on expressiveness in the playing and singing rather than on audiophile concerns like detail, soundstaging, tonal balance, etc.

Emotional response to music is a very personal matter. Listening to "Make Our Garden Grow," from Candide, played over a car radio affects me more profoundly than The Beastie Boys' Greatest Hits played over the world's best audio system (or live, for that matter). However, whatever kind of music you like—yes, even the Boys—my bet is that you'll find it more involving with the Avantgarde Uno.

If I were to attempt to analyze the Uno's appeal in audiophile terms, the obvious starting point would have to be dynamics. The Uno could play loud, very loud—and live music is sometimes very loud. Of course, given sufficient power, some conventional (ie, non-horn) speakers are capable of high sound-pressure levels, and speaker designers have started paying more attention to this attribute. (The Vienna Acoustics Mahler, which I reviewed in Vol.23 No.4, and the Paradigm Reference Studio/100 v.2, reviewed in Vol.23 No.6, are good examples of this trend.) However, the way the Uno presented high levels seemed qualitatively different. It wasn't just loud; it was effortlessly loud.

There's the obvious automotive analogy of 200hp from an 6-cylinder vs 200hp from a 4-cylinder engine. Even more apt is the comparison of a singer with a naturally big voice vs one with a smaller voice who is able to produce a big sound through sheer effort: Both singers can produce the same volume, but the one who doesn't have to "push" to get the effect is more pleasant to listen to. With the Uno, there was never any sense of "pushing," and no dynamic compression as things got louder.

Martin Colloms reported that the Avantgarde Duo has extremely low distortion; I expect the same will prove true of the Uno. The effect of this low distortion was an absence of volume-dependent strain, and I often found myself playing the system louder than is my custom. Played at realistic levels, Reference Recordings' Big Band Basie had a visceral impact, the combined weight of the brass filling the room with a power and punch that were simply breathtaking.

But the ability to produce high SPLs with low distortion was only part of the Uno's dynamic capability. The speaker was also able to project a great sense of quickness and dynamic tautness at moderate and low levels. The sound was very direct, as if the speaker was being driven directly by the signal, with no intervening electronics—an effect that may be related to the fact that there's no crossover between the amplifier and the midrange driver. In demos, there's a tendency to want to show off the speaker's ability to play loud, but the Uno doesn't have to be played loud to sound dynamic.

A friend who admits to preferring levels considerably lower than the typical audiophile—and who promptly asked me to reduce the volume from the blow-the-man-down demo level—said that he was most impressed by how the Uno maintained a dynamic feel even while playing at a "background" level. At every level, the ebb and flow of musical expression—ie, microdynamics—was communicated with a precision that went beyond any other speaker I've had in my listening room.

Dynamics are all well and good, but a loudspeaker can't be described as a high-fidelity device unless it's able to produce an accurate reproduction of the tonal characteristics of musical instruments and voices. The Uno did. Instrumental and vocal timbres were extraordinarily lifelike, and there was impressive tonal neutrality across the frequency range, bass and treble evenly balanced with the midrange. The tweeter managed the difficult trick of being sweet and revealing at the same time. Bass extension held up well to the low 20s, with lots of power on tap when required.

Matching a direct-radiating subwoofer with a horn midrange is no trivial task, but Avantgarde has done an admirable job, given the size and price constraints. (The $38,000 Avantgarde Trio has a horn woofer and four SUB225 CTRL PRO subwoofers, crossed over at a lower frequency than with the Uno.) After suitable tweaking of the subwoofer controls, the midrange/subwoofer blend was quite good, and the subwoofer came close to matching the midrange in tautness and agility.

Perhaps the most surprising aspect of the Uno's ability to present music was the way it seemed to transcend limitations in the quality of the source material. Poorly miked recordings, worn LPs, early digital transfers that I had dismissed as harsh-sounding—all came across as much more listenable, and at times were stunningly lifelike. The Uno was singularly lacking in hardness and grain, which lent an utter ease to the quality of reproduction. (The associated equipment I used for most of my listening, which included the Cary 2A3SE monoblock amplifiers and Bel Canto DAC 1, made a major contribution here.) A CD transfer of Mario Lanza's radio show, recorded in mono in the early 1950s (When Day is Done, RCA 63254-2), had me thinking that if Lanza were to miraculously appear in my listening room, this is just what he'd sound like. (Actually, this CD sounds better than most of Lanza's later studio recordings.) With every CD and LP I played, the Uno led me to feel that the music, performance, and recording were all better than I had realized.

The Uno's ability to present recordings in a favorable way didn't mean that it wasn't revealing of differences in recordings or associated components. In fact, the Uno's levels of clarity, transparency, and detail exceeded those of any other speaker of my experience. Whatever differences there were in the sound of recordings and equipment, the Uno allowed me to hear them. However, unlike speakers generally regarded as "analytical," it didn't thrust them at me in a way that interfered with the music.

Listening to the original cast recording of Hair through other speakers, I'd always thought that they must have recorded it with bandwidth- and dynamics-limiting filters. Through the Uno, all of this was plainly audible when I deliberately tried to listen for it, but unless I made a real effort to switch my mind into the analytic mode, I was able to simply enjoy the work as a dated but tuneful piece of '60s nostalgia.

The Uno also allowed me to hear the differences among the various dither settings of the Rotel RCD-991, and the beneficial effect of giving CDs the Auric Illuminator (footnote 2) treatment. The nature of the Uno is such that it revealed more clearly the effects of tweaks and component differences that might otherwise have been obscured, but its sound was so involving that I was less tempted to be forever tweaking or wondering if something needed to be changed in my system to get me closer to that ever-elusive live sound.

Being used to the standard-setting soundstaging and imaging capabilities of the Dunlavy SC-IV/As, and knowing that this is not usually considered to be horn speakers' particular strength, I thought I might find this aspect of the Unos' performance disappointing. As it turned out, the Unos were able to throw an extremely wide soundstage, with life-size images well-defined within the stage, lacking only the last bit of imaging sharpness provided by the Dunlavys. Listening position was not ultra-critical; in fact, I was able to get a good semblance of a soundstage when sitting directly in front of one of the speakers. (The soundstage was much better in the sweet spot, of course.) Initially, I had the impression that the images were somewhat larger than life, but this turned out to be an artifact of the tendency to play the speakers at levels louder than usual. The sense of depth and accuracy of placement in the distance was excellent; I was able to differentiate clickers at the 60', 70', and 80' distances in the depth test of Chesky's second jazz sampler and test CD (Chesky JD68).

And what about those infamous "horn colorations"? Virtually absent. The Uno certainly did not have the megaphone-like sound that people associate with horns, nor did it sound nasal, honky, or forward. From time to time I was aware of some resonance/unevenness in the lower midrange that may have been due to the horn loading, but its magnitude was low enough that it really didn't bother me. The fact is that every speaker has some characteristic that you will either get used to or find increasingly annoying. Some speakers avoid coloration in the usual sense, but have a kind of blandness that robs the music of excitement. The music presented by the Unos was so vibrant, so compellingly natural, that whatever coloration was occasionally noticeable (and it was only occasionally) seemed like a small price to pay.

Horns'n'SETs
There is a historical association between horns and single-ended triode (SET) amplifiers, an association that continues in the minds of many audiophiles today. But does buying the Avantgarde Uno entail having to get rid of whatever amplifier you're using now and buying a SET? And, in general, is this speaker so fussy about the quality of the associated components that only the best—ie, the most expensive—will do?

The answer I'd give to both questions is "Not necessarily." Because SETs have low power (except for ones using exotic tubes), they have to be used with high-efficiency speakers such as horns, but there's no reason to believe that the converse also holds.

As it happened, most of my listening was with Cary 2A3SE monoblocks (much beloved by Sam Tellig), which are prototypical SETs. They certainly have the genre's famed midrange magic, with a wonderful liquidity and a sense of space and openness. Although the rated output is only 5Wpc, they played quite loud enough for me, and the sound was so musically right that I can well understand the devotion that some audiophiles have for the horn/SET combination.

However, if I start to get analytic about it (there I go again...), I have to admit that the bass was somewhat on the mushy side, and there was some compression of dynamics at the high levels the Uno is capable of. The Balanced Audio Technology VK-60 (60Wpc, a modern bridged-SET design) had more extended, tighter bass and greater dynamic headroom, and its midrange was almost as good as the Cary's (footnote 3).

In both cases, the preamplifier was the $6000 Convergent Audio Technology (CAT) SL-1 Ultimate, with a digital front end costing $3-$5k, and power amps in the $4-$5k range—not quite price-no-object, but still pretty expensive. (The $1895 Cary SLP-50B preamp proved a credible alternative to the CAT: very sweet-sounding and musical, if less transparent and extended at the frequency extremes.)

To check out what the Uno might sound like with more moderately priced components, I set up a system consisting of a Rotel RCD-991 CD player ($1395) and YBA Intégré DT integrated amplifier ($2345, 50Wpc). Cables were still the pricey Nordost Quattro Fil/SPM, but I wanted to keep this part of the system as a constant. The results were more "mainstream" in tonal balance (less warmth, brighter) than the tube-based systems, but were very satisfying overall.

In general, I'd say that if you have a predilection for a certain type of amplifier design (solid-state or tube, single-ended or push-pull, Class Whatever), there's a good chance that it can be mated with the Uno. When you're shopping for an amplifier to match the speaker, keep in mind that the one with the lowest power in a given amplifier line is likely to be more than adequate, and usually sounds better than its higher-powered siblings.

Two technical aspects of the compatibility between the Uno and associated equipment that have to be considered carefully are preamplifier output level and amplifier gain. The Uno's high sensitivity makes the amount of residual noise in associated components critical, and some preamp/amp combinations that work well with less sensitive speakers are problematic with the Uno. The CAT preamp/Cary amp combination had an acceptably low noise level with the Uno, but the CAT driving a Bryston 9B-ST, an amplifier with extremely low inherent noise but high gain, resulted in annoyingly audible tube noise coming through the speakers. (The same preamp and amp with Dunlavy SC-IV/A or Vienna Acoustics Mahler speakers was dead quiet.) I'm told by Bryston's James Tanner that lowering their amplifier's gain is a simple internal modification involving the addition of some resistors; I assume this to be the case for other amplifiers as well.

Conclusions...
The illusion of "liveness" in reproduced sound is a delicate perceptual phenomenon dependent on the source material, equipment, room, and time of day, as well as the listener's mood and expectations. I have experienced this illusion in the past with some speakers in my system, but only rarely and in a fleeting manner. With the Avantgarde Uno, it was a frequent occurrence, and persisted for longer periods before something about the sound acted as a reminder that I was listening to a recording.

At times, the sense that these singers and musicians had somehow appeared in my listening room and were performing for me was quite spooky. Was this merely coincidence, or fortuitous system synergy? I don't think so. The effect was too consistent, and held up with changes in associated equipment. The Uno created the illusion of "liveness" better than any other speaker I've had in my listening room. In fact, I can think of few speakers I've heard anywhere at any price that sounded as convincingly "live" as the Uno. At just under $11k in the standard finish, the Uno is not inexpensive, but its sonic rivals cost very much more, and the Uno's high sensitivity means that you don't need an expensive high-powered amplifier to drive it.

In selecting a speaker, especially at the highest levels of performance, individual likes and dislikes play important roles. Some people may be bothered by the Uno's residual horn coloration, even though its magnitude is small. I wouldn't suggest buying a speaker based only on the recommendation of a reviewer—even if the reviewer is me! What I do suggest is that anyone who can afford speakers in this price range, and even those who can also afford speakers of the price-no-object variety, give the Uno a serious listen. It is simply that good.

Sidebar 1: Specifications

Description: Three-way, floorstanding loudspeaker with midrange and treble horns and powered sealed-box subwoofer. Drive-units: 1" horn-loaded inverted-dome tweeter, 4" horn-loaded midrange driver with 2.5" dome, two 10" cone woofers. Crossover frequencies: 220Hz, 3500Hz. Frequency range: 220Hz-20kHz (midrange/treble), 22Hz-300Hz (subwoofer). Sensitivity: !w100dB. Nominal impedance: 8 ohms. Recommended power: greater than 5W. Power handling: 100W. Subwoofer amplifier power: 200W.
Dimensions: 57" H by 22.5" W by 28" D (mid/treble); 22" H by 12" W by 22.5" D (subwoofer). Weight: 153 lbs.
Finishes: Standard: polished white ABS Uno), SUB225 CTRL PRO subwoofer in Nextel; horns in metallic lacquer, add $1000; subwoofers in matching lacquer, add $1000.
Serial numbers of units reviewed: 07020011/12.
Price: $10,970/pair. Approximate number of dealers: 20. Warranty: 10 years for material fatigue, 5 years for color coating, 1 year for all electronic components.
Manufacturer: Avantgarde Acoustic Lautsprechersysteme GmbH, Nibelungenstrasse 349, 64686 Lautertal, Germany. Tel: (49) 6254-306-100. Fax: (49) 6254-306-109. Web: www.avantgarde-acoustic.de. E-mail: avantgarde-acoustic@t-online.de. US distributor: Avantgarde-USA, 6445 Calamar Drive, Cumming, GA 30040. Tel: (800) 944-9537, (770) 777-2095. Fax: (770) 777-2108. Web: http://www.avantgarde-usa.com/. E-mail: hornguys@aol.com.

Sidebar 2: A Dilemma

From early on during my time with the Unos, I started thinking that here was a speaker that had what it takes to dethrone the Dunlavy SC-IV/A as my reference. Continued experience reinforced this notion, but, as I thought about its implications, it became clear that the selection of a reviewer's reference speaker has to involve more than personal preference.

In addition to delivering sound quality, a reference component also has to be suitable for reviewing purposes. Alas, the Uno's design—high sensitivity, integral powered subwoofer—makes the speaker too different from the type of loudspeaker owned by most Stereophile readers, so that reviews of electronics (especially amplifiers) done with the Uno would have limited generalizability. The speaker's size and shape are such that shifting them in and out of the listening room to accommodate other speakers would not be practical. And yet, I didn't want to give up the sound of music as presented by the Unos. What to do...what to do...

Could I set up a second audio system in the living room as an alternate reference? (I already have a home-theater system in the basement.) You'll recall that's where I first set up the Unos, and they sounded pretty good there, too. But that was on a temporary basis. Would my wife, Beverley, accept them as a long-term part of our living-room décor? I knew that she really liked these speakers, but did she like them that much?

Her response: "Only if I can play my records more often!"

Jim Smith is getting a check. The Unos are staying here.—Robert Deutsch

Sidebar 3: Associated Equipment

Analog source: Linn LP12 turntable (fully updated), Linn Ittok tonearm, AudioQuest AQ-7000nsx cartridge.
Digital sources: PS Audio Lambda II CD transport, Muse Two Ninety-Six and Bel Canto DAC 1 digital processors, Rotel RCD-991 CD player.
Preamplifier: Convergent Audio Technology SL-1 Ultimate, Cary SLP-50B (with shunt volume control).
Power Amplifiers: Cary 2A3SE monoblocks, Balanced Audio Technology VK-60, Bryston 9B-ST, YBA Intégré DT.
Cables: Digital: Illuminati Orchid, Kimber Illuminations D-60. Interconnects: Nordost Quattro Fil, TARA Labs The Two. Speaker: Nordost SPM Reference, TARA Labs The Two. AC: TARA Labs Decade.
Accessories: PS Audio P300 AC synthesizer (used with preamplifier, analog and digital sources), Bright Star Little Rock (atop CD transport), Nordost PP4 Ti and PP4 Al Pulsar Point component supports, Arcici Suspense Rack, PolyCrystal amplifier stand, Furutech RD-1 CD demagnetizer, Auric Illuminator CD treatment, four Argent RoomLenses.—Robert Deutsch

Sidebar 3: Measurements

Like Bob Deutsch, I also had problems with AC noise when I measured the Uno. (For logistical reasons, I measured a different sample, delivered to Santa Fe by Casey McKee.) The DRA Labs MLSSA system I use inhabits an ancient 486 computer, and it turned out that the monitor and computer were plugged into a surge suppressor with sufficient series resistance to introduce a ground loop. And at an estimated 102.5dB(B)/2.83V/m voltage sensitivity, the Uno faithfully revealed the problem.

As well as its astonishingly high sensitivity, the Avantgarde speaker will be an easy load for the partnering amplifier to drive: its impedance (fig.1) hardly drops below 8 ohms, with a mainly resistive phase angle. The small peak at 19kHz will be due to the tweeter's primary dome resonance, but the impedance plot is otherwise free from the narrow peaks usually seen with a horn-loaded speaker.

Fig.2 shows the nearfield response of the subwoofer module with the crossover set to 220Hz (top curve) and 90Hz (bottom curve) and at the three indicated intermediate frequencies. (The extension switch was set to 20Hz for these measurements, and you can see that the module's -6dB point indeed lies at 20Hz.) The first thing to note is that, at the extreme settings, quite large rotations of the control introduce very little change in the response, while in the center, even quite small rotations make a large difference. Optimizing the subwoofer setting will need a delicate touch on this control. Second, note that at the more extended settings, the subwoofer extends almost an octave higher in frequency than the indicated "220Hz." This has implications for the speaker's setup that can be seen in the next graph.

Fig.2 Avantgarde Uno, nearfield woofer responses with crossover set at its maximum (220Hz), minimum (90Hz), and three intermediate frequencies.

Fig.3 is the Uno's quasi-anechoic response, taken at the manufacturer's recommended microphone distance of 63". (A similar measurement taken at my standard 50" distance differed only in the low treble, and then only regarding the heights of the peaks and dips.) The measurement axis was again the manufacturer's recommendation: midway between the center of the midrange and tweeter horns, a sensible 36" from the floor. The lack of energy in the lower crossover region is most likely due to interference resulting from the overlap of the midrange horn and the woofer. It suggests that the woofer would integrate better at this relatively close distance if its electrical polarity were to be inverted. Unfortunately, the need to return the measurement sample of the Uno to its Austin, Texas owner before I could process the measured data meant that I could not further explore this aspect of the speaker's performance. But if you're bothered by a thinness in the Uno's lower mids, I encourage you to experiment by changing the polarity of the speaker leads connecting the woofer terminals to the upper-range units.

Fig.3 Avantgarde Uno, anechoic response on design axis at 63", averaged across 30 degrees horizontal window and corrected for microphone response, with the nearfield woofer response plotted below 150Hz.

Higher in frequency, though there are a series of small peaks and dips evident, the overall balanced trend is very flat—certainly the flattest I have personally measured with a horn speaker. The very top octave is slightly hotter than the region below, which I could hear in the nearfield as just a slight emphasis to the hissy MLSSA noise when I was measuring the speaker. However, I note that RD was not bothered by this excess high-treble energy, which means that in-room, it might well be compensating for the speaker's off-axis behavior.

I have shown the Avantgarde's lateral off-axis behavior in two ways: fig.4 shows the actual responses to the speaker's sides; fig.5 shows just the differences between the off-axis responses and the central, design-axis response. First, note the flare to the speaker's sides in the lower midrange. The cancellation notch between the midrange and the woofer occurs exactly on-axis and becomes less deep off-axis.

Fig.5 Avantgarde Uno, lateral response family at 50", normalized to response on design axis, from back to front: differences in response 90 degrees-5 degrees off-axis, reference response, differences in response 5 degrees-90 degrees off-axis.

Second, note that, with the exception of the upper crossover region, the "contour lines" are very even. The physical design of the two horns and the frequency ranges they cover have been carefully chosen to given a consistent radiation pattern. It can be seen that the midrange horn does have a slightly wider dispersion than the tweeter horn, however, the latter's output falling uniformly by 24dB approximately 45 degrees to the speaker's sides. All things being equal, this would tend to make the speaker sound rather dull in large, overdamped rooms. But given the on-axis rise in response, the speaker's highs in more typical rooms will actually tend to sound better balanced as a result.

In the vertical plane (fig.6), the high frequencies are well-maintained in the ±10 degrees shown. However, various peaks and dips occur off-axis in the low-treble, suggesting that the listener sit with his or her ears on the intended axis.

Fig.6 Avantgarde Uno, vertical response family at 50", normalized to response on design axis, from back to front: differences in response 10 degrees-5 degrees above axis, reference response, differences in response 5 degrees-10 degrees below axis.

In the time domain, the Uno's step response (fig.7) appears to indicate that the tweeter is connected in inverted electrical polarity, the midrange and woofer in positive polarity. And not surprisingly, given the physical displacement of the drive-units, the speaker is not time-coherent. The cumulative spectral-decay plot (fig.8) is quite hashy, but this is not, I suspect, due to resonances but to the presence of early reflections. The lip of the midrange horn, for example, is clearly in the tweeter's acoustic environment (footnote 1).

Fig.7 Avantgarde Uno, design-axis step response at 50" (5ms time window, 30kHz bandwidth).

Fig.8 Avantgarde Uno, cumulative spectral-decay plot at 50" (0.15ms risetime).