Avantgarde says that current-production woofer enclosures have factory-fitted inserts for floor spikes. In addition, longer auto-switching "on" times are defined for the woofer electronics, plus a continually on switch. Future iterations of the Duo will also have an additional control providing an adjustment of +6, 0, –6dB centered on 25Hz. This will help the speaker cope with home-theater power requirements.
Sound
No one should have to make allowances for a horn design. Rather, it should be judged on its overall merit; then its balance of favorable qualities, assuming them to be sufficient, can be weighed in its favor. Previous encounters with horns had left me concerned about their characteristic colorations, but I needn't have worried. The Duo was comparatively low in coloration; it sounded different from a conventional speaker, yes, but no more colored than many a fine, reference-grade conventional loudspeaker. No, this horn speaker didn't sound like a trumpet, nor did it have megaphonic projection. In fact, it was surprisingly unobtrusive in acoustic terms, though it was hard to weigh how that dramatic up-front appearance influences one's aural judgment.
First impressions were of a powerfully wide frequency range, of an evenly balanced design with an exceptional dynamic range. Audiophiles speak of very big amplifiers (ie, over 250Wpc) as sounding "effortlessly dynamic" with a given speaker. However, a firm distinction needs to be made between that kind of dynamic range, which involves raw amplifier power and correspondingly high peak currents flowing through the speaker's voice-coil, and that produced by a loudspeaker possessing genuinely high efficiency. The Duo requires very little current, and its dynamics are of a genuinely different kind (footnote 1).
The Duo offered excellent microdynamics; I was made aware of a tactile quality more closely associated with live musical instruments than with heavy speaker diaphragms. Electrostatics can suggest this through sheer transient purity and accuracy, but somehow don't sound this immediate. With the Duo, transient-rich percussion reached out in a most appealing way.
Second, the Duo had a breathtaking dynamic range, second in my experience only to that of the Wilson X-1/Grand SLAMM, and then only in the bass. In fact, the Duo probably outreached the SLAMM in the mid and treble. Big orchestral climaxes were truly thrilling—all-encompassing, concert hall–like sensual assaults. There was no hint of compression or failure of clarity at high levels.
The Duo was highly sensitive. Not only did a variety of different amplifiers drive it with ease, very little power was required to drive it at all! For a joke, I connected the speakers to a stereo portable radio with a couple of clean watts per channel and got genuinely high volume levels. Avantgarde told me that when used in some German discotheques, 20W power amps had proved ample!
Putting aside those sound-quality aspects specific to horn technology, I tried to view this speaker dispassionately and put it in the context of other similarly priced systems in the $10k–20k range. That includes (among many others) a number of important examples, from the Wilson WITT Series II and WATT/Puppy 5 to the Avalon Ascent, the MartinLogan ReQuest, the EgglestonWorks Andra, and the Audio Physic Caldera 2.
The Duo's trump card is its midrange, that single horn covering 170Hz to 2kHz in a single pass. So much goes on in this region, and the Duo rewards its owner with excellent linearity, clarity, detail, separation of instrumental lines, immediacy, and natural attack. Here the Duo reached beyond its peers. Moreover, allied to a harmonically pure, comparably resolved and transparent SET amplifier, that feeling of an aurally distortionless, tactile, and transient immediacy was significantly enhanced.
If these were the Duo's strong points, its weaknesses were all moderate in degree. However, they were apparent in direct comparisons with other high-performance loudspeakers. Presumably aided by its direct-coupled power amplifier, the Duo's bass was pretty good by subwoofer standards, and will satisfy many listeners. However, it didn't wholly integrate with that lightning-fast midrange, sounding a little displaced in time and agility. In critical comparison with the best freestanding speakers, the Duo showed some shortfall in tune-playing clarity and crisp control.
For whatever reason, the high-frequency horn was not quite as aurally successful as the glorious midrange unit. The treble stuck out a little compared with the best direct-radiators, sounding forward of the mid and presence ranges. This lead to some additional vocal breathiness and exaggerated the airstream sounds of woodwind instruments. The balance was also lifted in the high treble, sometimes achieving an attractive airiness and sparkle, but at other times adding noticeable "tizz" and "zing."
The high treble occasionally emphasized tracking and similar jitter-related distortion, suggesting some mild resonance or roughness at the edge of audibility, this less noticeable with tube than with solid-state amplification. Despite this, the treble was notably smooth, with good violin timbre and pure, unstressed vocal sibilants.
There was a trace of horn character in the midrange best described as a hint of "echo," though not so much as to obscure the inherent clarity or to shift tonal balance. In the upper mids, some percussion (eg, woodblock) was emphasized, but not to the point of oppressive ringing or hardness (see the measurement results on the midrange horn). No coloration as such could be reliably ascribed to the structure of the horns themselves, or to the bass cabinets.
Stereo image focus was fairly good, the phantom center image wider than usual but not unduly so. In general, I obtained good image depth and transparency from the Duo. Image stability was very good, and notably unaffected by sound level. I heard less room-excited ambience; the sound was clearly more directed (as horn theory teaches us) toward the listener, with less room contribution than usual in the mid and treble. This kind of room drive took a little getting used to; I consider it a significant component of the "difference" felt to exist between the horn and direct-radiator technologies. Of course, in some rooms with awkward, asymmetrical dimensions and acoustics, the horn speaker will provide a more consistent and more accurate sound at the listening position because of its controlled directional behavior.
You might suppose that a horn system would favor some instrumental sounds more than others, but I didn't find this to be so. Orchestral brass sounded very good, but the Duo also proved surprisingly evenhanded on solo piano. Likewise, large-scale choral music was impressive, with excellent separation of solo voices from the chorus. Orchestral stages were well laid out, with satisfying reach to subtle low-level percussion playing at the back of the band.
Those magnificent dynamics and free-sounding percussive transients helped give this speaker a lively, upbeat quality suited to rock and classical music. Pace and rhythm were pretty good when adjusted for an optimized "dry" setting for the chosen alignment of subwoofer and room location.
Bass reached to a solid 30–35Hz, nearer to 40Hz when driven hard—worthy, but not in true subwoofer class. The speaker could be driven to truly high sound levels without premature collapse of the active bass; the designers have got the matching power envelope more or less right.
Finally, there's the Duo's appearance, which some listeners felt approached engineering expressed as art, while others found the horns too large and threatening a presence to blend into a domestic setting. It speaks to me of modern loft-apartment living, places with large windows and expansive views.
Conclusion
To appreciate the qualities of Avantgarde's Duo, it's necessary to discard your prejudices, holding back from the analytical view that all must be in perfect balance. The Avantgarde Duo certainly is not perfectly "balanced" in performance, and maybe a high-efficiency horn can never be when compared with well-optimized, lower-efficiency, direct-radiator speakers. Yet it also argues well that balance isn't everything. There's true sonic value in that majestically broad, dynamic midrange, in the obvious microdynamic delicacy and accuracy, the near-zero distortion, the potential for very high sound levels, the easy amplifier loading, and this speaker's compatibility with low-powered purist triode amplifiers. And make no mistake, the rest of it's pretty good too—though you'll need to listen for yourself to really appreciate the quality of the entire creation. It will work with any good amplification, but truly sings with small zero-feedback triode amps—surely a match made in heaven? For me, the Avantgarde Duo proved to be neither a review reference nor a monitor speaker, but I shall not forget my time with it in a hurry.
Footnote 1: I've found that a simplified view of distortion behavior and dynamic range in moving-coil speakers can be directly related to the required input current, without specific consideration of either electrical power or sound level. From this standpoint, which hinges on the inherent nonlinearity of the conventional electrodynamic transducer, the design that requires the least current is potentially the most linear and most dynamic. My measurements reveal that the Duo attains a high 110dB SPL on an input current of 0.7A RMS; most of the bigger three-way direct-radiating speakers (4 ohms impedance/86–88dBW sensitivity) will require some 6.5A to achieve this same loudness.
No one should have to make allowances for a horn design. Rather, it should be judged on its overall merit; then its balance of favorable qualities, assuming them to be sufficient, can be weighed in its favor. Previous encounters with horns had left me concerned about their characteristic colorations, but I needn't have worried. The Duo was comparatively low in coloration; it sounded different from a conventional speaker, yes, but no more colored than many a fine, reference-grade conventional loudspeaker. No, this horn speaker didn't sound like a trumpet, nor did it have megaphonic projection. In fact, it was surprisingly unobtrusive in acoustic terms, though it was hard to weigh how that dramatic up-front appearance influences one's aural judgment.
To appreciate the qualities of Avantgarde's Duo, it's necessary to discard your prejudices, holding back from the analytical view that all must be in perfect balance. The Avantgarde Duo certainly is not perfectly "balanced" in performance, and maybe a high-efficiency horn can never be when compared with well-optimized, lower-efficiency, direct-radiator speakers. Yet it also argues well that balance isn't everything. There's true sonic value in that majestically broad, dynamic midrange, in the obvious microdynamic delicacy and accuracy, the near-zero distortion, the potential for very high sound levels, the easy amplifier loading, and this speaker's compatibility with low-powered purist triode amplifiers. And make no mistake, the rest of it's pretty good too—though you'll need to listen for yourself to really appreciate the quality of the entire creation. It will work with any good amplification, but truly sings with small zero-feedback triode amps—surely a match made in heaven? For me, the Avantgarde Duo proved to be neither a review reference nor a monitor speaker, but I shall not forget my time with it in a hurry.
Footnote 1: I've found that a simplified view of distortion behavior and dynamic range in moving-coil speakers can be directly related to the required input current, without specific consideration of either electrical power or sound level. From this standpoint, which hinges on the inherent nonlinearity of the conventional electrodynamic transducer, the design that requires the least current is potentially the most linear and most dynamic. My measurements reveal that the Duo attains a high 110dB SPL on an input current of 0.7A RMS; most of the bigger three-way direct-radiating speakers (4 ohms impedance/86–88dBW sensitivity) will require some 6.5A to achieve this same loudness.
