Avantgarde Acoustic Duo loudspeaker

Few designers are drawn to create horn loudspeakers. Most people’s experience of horns is based on the resonating, overdriven, often overloaded PA installations heard at rock concerts and similar events. These commonly heard unmusical noises and colorations are ever-present in designers’ minds. But good-sounding horns do exist; over the years, some noteworthy commercial examples have appeared, though few have been full-range.

True full-range horns include the classic Voigt (1936) and Klipsch (1945 onward) designs, the former most famous for a corner horn that ingeniously exploited the geometry and boundaries of a room corner to expand the effective mouth area of the bass horn, thus extending the bass response.

Paul Klipsch, who celebrated his 94th birthday on March 9, 1998 mastered the art of rear pressure loading and horn folding to create more compact designs, though they were still relatively bulky when compared with direct radiators. The inescapable fact is that a good wide-range horn remains a large acoustic object. Avantgarde Acoustic’s designer, Matthias Ruff, has accepted—even exploited—this obstacle by building some of the most visually arresting horn speakers of recent years. The present range comprises four models; even the smallest, the $9100/pair Uno, is large, standing almost 5′ high, with a wide-range mid-horn almost 2′ in diameter.

The larger Duo is also a two-way horn design, with an active reflex-loaded woofer covering the bass region. Above it in the Avantgarde line are two versions of the Trio ($37,000, depending on form and woofer specification), one built as a stylish curved array, the other with a more compact, almost in-line horn configuration. As its name suggests, the Trio is a three-way model, its largest horn extending down to 100Hz, and with a mouth area double that of the smaller midrange horn used in the Duo. The Trio includes four subwoofers for increased dynamic range.

The Duo’s midrange horn covers an exceptionally wide bandwidth—some four octaves. (Typically, a midrange driver covers 2.5–3 octaves.) Such a wide bandwidth is a key factor in reducing the characteristic signature of the main horn. Both the mid and treble sections operate at high efficiency and with relatively low power compression at their throats to maximize linearity. This ensures low distortion and fine dynamic expression over the bulk of the operating range. An extended-range bass horn needs to be huge. so for the Duo the designer has chosen a legitimate alternative: an active woofer system, one enclosure per channel, integrated into the stacked enclosure frame. A three-pillar steel tube frame is used to support the horns on lateral fixtures, these adjustable for listener height.

The horn design is proprietary to Avantgarde Acoustic and runs close to a tractrix profile in the early section before flaring at a rate more like that of a trombone bell than a sphere. The aim is to smooth the transferred acoustic impedance in the low range to help control the usual ripples in power due to finite horn size, and diffraction at the exit flare or mouth.

No less than 26″ in diameter, the midrange horn is asymmetric, and dominates the system’s physical appearance. Some 13″ down its throat lies a 3″ hard dome plug formed from resinated pulp. This is a close-coupled “compression” dome energized by a 7″ Kevlar-coned drive-unit behind it.

In high-power PA horns, the back of this driver would be enclosed to generate a second resonance for reterminating the falling horn impedance at low frequencies. Instead, Avantgarde leaves the back open, freeing the system of further resonance via a transmission line venting via slots molded in the back section of the housing.

The main horn crosses over at a specified 2kHz to the smaller 7″ horn, this energized by a 1″ concave-dome driver. The flare rates of this small horn parallel the design of the mid, but are appropriately scaled. Considerable care has been taken with this design, which has a user-replaceable diaphragm, a double suspension, and a phase-correction plug at its throat. As with the mid driver, the high-frequency unit is vented through the pole and is terminated by a transmission line designed to be free of resonance.

Another aspect of the physical design concerns the intended placement of the treble horn in line with the listener’s ears. The midrange horn is therefore significantly high, both acoustically and visually, at 50″ or so from the floor.

Woofer connection couldn’t be easier. Its integral amplifier is driven from the speaker’s high-level input terminals on the rear of the central, high-frequency housing. Sensibly, the signal take-off is not only at relatively high impedance (about 1k ohm), but it’s also balanced transformer-coupled. This floats the woofer ground, avoiding hum loops and easing connection to balanced and bridged designs such as the Krell FPB series.

The 45 liter woofer enclosure has a pair of 7″ long-throw bass drivers reflex-loaded by a fairly large, slot-loaded port. The duct output faces front and is placed between the inward-angled drivers to deliver superior low-frequency integration. Reflex tuning is at approximately 35Hz, promising in-room drive down to 30Hz if the system is optimally set up and aligned.

Although rated at 4 ohms impedance, the subs are of relatively high sensitivity: 95dB/W into 8 ohms at 2.83V. In practice, the true figure is probably a little higher, given their floor placement and corresponding boundary gain. Assuming a 97dB low-frequency sensitivity in a typical US home, the woofer’s 90–100W power amplifier can potentially deliver bass levels of some 110dB over the listening area—a decently loud level.

In contrast, the Duo’s horn sections, driven by the owner’s main power amplifier, will require much less power. With a specified sensitivity of 101dB/W, they should be compatible with many low-powered amplifiers, including the best of the single-ended triode (SET) designs. For example, to provide maximum output from the Duo, some 110dB in the listening region, will need just 15W! To further ice the compatibility cake, the system impedance is rated a pretty smooth 8 ohms, so amplifier-matching problems will be minimized.

To give you an idea of the Duo’s real-world sensitivity: A volume setting of “83” on the Conrad-Johnson ART preamp gives a really loud sound level with the Wilson Audio WITT Series IIs or WATT/Puppy 5s; the Duo requires a setting of only “65” to achieve the same level. “88” on the ART’s volume control was close to clipping my Krell FPB 600 (over 600Wpc), so a volume of “65” into the Duo translates into a program maximum of around 60W—an easy cruise for the Krell but essentially at overload point for the Duo’s bass and horn sections. When I drove the Duo this hard, the beginnings of horn throat distortion were apparent; taken to the limit, some horns can produce that “crackle” of the air being driven nonlinear. I would say that you would never need more than 40 or 50W to drive the Duo to its practical limit; just 8–10W will go a long way with a speaker of such high sensitivity.

This is extraordinary. Here we have a speaker that claims to offer powerfully satisfying and user-tuneable active bass, plus a combination of loading and sensitivity that would allow a low-powered SET amplifier to roar like a lion, producing genuinely high audiophile sound-pressure levels even in larger rooms.

I tried the Duo in two environments: my main, well-bookcased listening room, and a smaller room with a livelier acoustic. It worked well in both, showing good room compatibility, an aspect confirmed by the later technical analysis.

Sound radiation from horns differs from that produced by direct radiators mounted in boxes. Cabinet diffraction is absent, but the horns have their own distinct properties. One concerns a minor but audible variation with distance. I found that the midrange became lighter in character as I moved away from the Duos—say, from 12′ to 18′. The richest sound was attained nearer to 11′. In addition, while the general character was relatively insensitive to angle or height, a very positive result—an unmistakable tightening of focus, coherence, and transparency—was obtained when the horn axis was precisely aligned on my ears in a classic equilateral triangle.

Other factors influencing the placement included the distance from rear and side walls, this more specifically associated with the woofer system and its optimum boundary conditions. In this respect the Duo behaved much like a floorstanding three-way speaker with an extended low range. Like the WITT II, it ended up placed about 5′ from the side walls and just over 7′ from the rear walls in my larger room.

Some experiment was necessary to obtain the best overall sound, as not only should the woofer be physically aligned with the local boundaries, it must also be optimized for level and crossover frequency. The woofer also has a polarity-invert switch to cope with circumstances where a local standing wave exists at the crossover frequency. I ended up with an in-phase connection in both my rooms and tended to set the bass on the dry side—a European balance, if you will.

If the woofer level was set on the high side, there was a tendency for it to stand apart from the horn sections and thus slow the pace. These system settings are partly matters of taste and preferred program. I continued to evaluate the Duo confident in the knowledge that its low end could be tailored for virtually any program or room, whether of masonry or timber frame construction.

As supplied for review, the Duo woofer enclosure was joined via semiflexible mounts to the side frames, the latter secured to the floor with 10mm spikes (or self-aligning feet). I got the best results mounting the bass enclosure directly to the floor using third-party cones, thus freeing most of the gravity load from the speaker frame and giving greater stability with respects to the woofer’s relationship to the floor boundary.

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Avantgarde Acoustic GmbH

US distributor: American Sound of Canada Inc.

Richmond Hill, Ontario L4E 3M7




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