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.

Avantgarde Acoustic GmbH
US distributor: American Sound of Canada Inc.
Richmond Hill, Ontario L4E 3M7

dc_bruce's picture

driven by an all-tube BAT electronics chain, including phonostage. The bass was a mess, perhaps because the person who set the system up didn't take a lot of time to dial the bass system in. On the other hand, the rendering of Ella Fitzgerald's voice was simply extraordinary in its realism and palpability. So much so, that I forgot to even listen for audiophile things like imaging, soundstage depth and so on.

Even in today's dollars, these are out of my reach financially; and, obviously they visually dominate any normal-sized room. But, if I did have the room and the $$$, these sure would be tempting, especially if a good digital LF room correction system were applied to the box woofer.

FWIW, I have heard Klipschorns in multiple settings, driven by a variety of electronics; and they never tempted me in the least.

Anton's picture

Modern "high end" is a full decimal place to right in the wrong direction.

I know, shut up and get back to my Silver Bullets in my single wide.

thatguy's picture

I wonder as the price goes up what the point is where the high price actually becomes a good factor for a certain type of well off shopper.
I'm sure there are those that don't want it if it is at all affordable. The crazy high price adds to the uniqueness and lowers the chance that anyone that visits them will have the same.

dc_bruce's picture

By "today's dollars," I meant the purchase price reported in Collums' review, as adjusted. $80,000? That's truly insane.

Glotz's picture

LMAO... You funny.

I just bought a case of PBR and I'll be over in 10 minutes!

partain's picture

What is meant by a "dry" chosen alignment of subwoofer and room location ?

tonykaz's picture

Some Bicycle Box cardboard, a razor knife, a glue gun and some Scans Drivers will provide anyone with super performance at Schiit Level Prices.

Avant is selling Artistic and Active Sculpture Art to wealthy or near wealthy Socials.

apparently only comparable to Wilsons.

This reads like prospective Marketing copy.

Tony in Venice

JHL's picture

...there you go again.

Does the inherent corruption of material currency ever weigh just too heavily on the socially deeply, deeply virtuous? Must be exhausting.

tonykaz's picture

Are we discussing DIY or something else ?

What is "inherent corruption of material currency" , are you referring to $80,000 Horn Loudspeakers?

Tony in Venice.

JHL's picture

...what we're "discussing". I thought the context was the review but apparently it's really the unsavory dollar and how it comports with your next social formulations on acceptability.

tonykaz's picture

Are you objecting to an opinion?

Nearly everything is this Publication is solidly Opinion Based. ( Mr. JA1's measurements are not )

Of course you have your opinions, don't you? Maybe you aren't allowed to voice your points of view, except to mention mine.

I don't mind you making acidic comments, they would probably be useful if they were probative.

Every single reader of Stereophile has thier own unique opinions and points of view, based on their personal Life experiences .

Bon Vivant

Tony in Venice

JHL's picture

...on the nature of opinions before.

First, they are not a right because opinions and rights are in different domains. There's no conflation of opinion and *speech* insofar that the opinion, as I once said, that I can walk into a speeding bus unscathed is obvious nonsense. I may claim a right to say so, but it remains rubbish.

Second, the right to speech is a construct of structural contract in the west and obviously has no bearing on the comments section in Stereophile - different domains here again. Whether you can make claims about audio tantamount to walking into busses and defend them as tacit rights is also crap.

Third, therefore these abstracts, as you stretch them about, don't give you cover. We're not talking about rights and we're not restricting yours. You making vague references to oppression as some *further* moral slight is just as illogical.

The heart of your inferences hereabouts are commonly that a large price tag carries all this social baggage that somehow involuntarily induces your negative value judgements on others as if such were some cosmic pronouncement. Some universal truth.

You can hold and say whatever dumb opinion you wish but that doesn't validate it. Speaker parts in bicycle boxes is only a tortured commentary on the manufacturer in the review above in your own odd compulsion. The rest of us don't care. I know I don't.

Which is my opinion. Here's another opinion. Let the reviewer have his.

tonykaz's picture

I'm reviewing the reviewers. ( journalists ) ( I love Stereophile and admire the writers and thier work, for the most part )


you don't have the right to limit others points of view. Do you?

Of course, I can understand that you have anxieties that you need to present but I have no obligation to honour you or negatively respond to you trolling and I won't !

You certainly write an interesting complaint.

Mr.HR suggests that the people that buy this super expensive stuff don't actually read Stereophile. Do you own Avantguard ? or horns in general ? Hmm.

I've owned horns ( klisph ) and built horns.

Tony in Venice

JHL's picture

Reviewing the reviewers - if that's what you're doing when you divine the supposed intersection of price, social class, and the character of others - has nothing to do with this "right" you've just introduced.

As I just noted, obviously rights lie elsewhere entirely. Rights also fail your formulation when you challenge mine, such as they are, to note your using these threads to comment like you do. How has anyone abused a right somehow "limited" your remarks? I began with *there you go again* because there you go again.

This isn't trolling, Tony. It's challenging the *anxious* compulsion to use a hifi magazine to launch off-topic critiques not supported by evidence.

Social warriors overlook the affronts they commit correcting a world whose imagined affronts they can't take.

AJ's picture

Some Bicycle Box cardboard, a razor knife, a glue gun and some Scans Drivers will provide anyone with super performance at Schiit Level Prices.

Send me the plans so I can build it Tony, I have all those ingredients. I have tons of Amazon cardboard these days! Is that of audiophile quality like "Bicycle box"?



tonykaz's picture

Bike Shops have plenty of large double thickness Boxes for FREE.

Experiment with design, copy Avant but with 8 sides or copy Klipsch.

The Horn importance comes from it's inherent 9 db gain, driver coupling to the horn can be easily worked out.

Large Bicycle Boxes are nearly inert but they can be doubled up with glue-on added mass patches in places where you discover sympathetic resonances.

It's great fun and you may become one of the great loudspeaker manufacturers.

The drivers are the singing voice, the horn is mechanical amplification.

Tony in Venice

ps. you might also invest in a bicycle and become completely Solar Powered ( like we were 200 years ago ), my bike gets 10miles to the Cheeseburger.

Cooking Man's picture

I owned a pair of Duo’s from 2001 to 2017. These had the next generation subs from Martin’s review pair. If I recall correctly the Duos (or was it the Unos?) were Stereophile Speaker of the Year one year in the early noughties.
I loved the Duo’s for their slam,dynamics,visceral presence and sheer joie de vivre.
However as the years rolled by their Achilles heal become more and more troubling. In my system in my room with my music the crossover between the glorious midrange horn and the treble horn was the problem. I tried numerous amps over the years (Quicksilver,Pass Aleph,Mark Levinson,Graff,First Watt and latterly Mactone), performed the factory Omega upgrade and around 5 years ago spent a small fortune on a custom cross over with silver Dueland components. All enhanced the great qualities BUT only served to emphasise the Achilles heal.
I endlessly fiddled with positioning,tilt,footers,cables blah blah. Sometimes that was fun. Increasingly it was frustrating. In the end I threw in the towel. I borrowed in home loan a pair of active ATC SCM100’s and they never went back.
I did love the Duo’s but at times I hated them and in the end a clean break divorce was the best outcome. I miss their seat of the pants thrill ride of aural delight. I don’t missed the screeching treble,vicious sibilants and endless head scratching.

Jack L's picture


So you cook up the wrong way ! Sorry you went thru so much frustration before you finally gave up the huge horns.

In the demo of the Trio+huge Basshorn in Vantgarde showroom years back, my quality-oriented ears just could not handle the huge
yet clinical sound, I had to call for time-out after only 10 minutes. So from sublime to ridiculous, we swiched to a pair of
BBC monitor Rogers type compact standspeakers, nothing else chanaged.

I enjoyed the demo for 2 hours!

ATC England supplies 5-star ranked loudspeakers for recording studios & for home. Are your classical or tower or professional model ?? Excellent choice, my friend !

Listening is believing

Jack L

Cooking Man's picture

Thanks Jack but please don’t get me wrong. I had many years of pleasure with the Duo’s. As the review noted in some areas they were revelatory. And still would be. I believe my room at 19x20x9 feet was too small to allow the horns to integrate better. I couldn’t sit more than 12 feet from them. That why I said,my room,my music and,I should have added,my ears. All speakers in a room are compromised-it’s just a question of where those compromises and weaknesses are and how they affect the emotional response of the listener.
I bought the Classic ATC SCM100’s and a pair of Track Audio Reference stands. Hooked up to subsequently bought CH Precision L1/Xi and Ypsilon VPS100 phono stage my music delivers thrills and enormous pleasure. I’m very fortunate and grateful to be able to own such extraordinary equipment.

Jack L's picture



A 'horn' loudspeaker is built of a compressor driver with narrow beam-like directivity & a horn-shaped diffuser to spread out the dispersion.

Sitting too close we listen mainly the beaming from the centre compressor driver, sharp like cutting our heads off: sorta torture!

Sitting too far away we will virtually perceive much larger than life-size imaging of the instruments & the performers. An oboe will look like a bass bassoon. An soprano's mouth will look larger than her head !!

Two audio fans invited me to check out their Alec/JBL horns on 15" woofer boxes. Frankly, I was not impressed at all: plenty of sound, pretty shy in music delicacy & emotional feeling

Listening is believing

Jack L

denesdr's picture

That's not true at all. A compression driver have very wide dispersion on it's own and mainly the attached horn/waveguide sets the desired radiation pattern/directivity. True that there are sharp sounding compression drivers but there are right sounding compression drivers aswell, as with any type of tweeters.