Avantgarde Reviews: UNO - Udo Ratai, Image HiFi

Horn loudspeakers were born at a time when [tube] amplifier watts were rare. Today the opposite often applies. Monstrous amplifiers and 'thick as your arm' speaker cables drive low-sensitivity High-End monitors. Has the world turned upside down?

Horn loudspeakers rock the foundation of ideologies - you either love them or hate them. Horn loudspeakers have their fanatical devotees as well as their unconvinced critics. The latter should listen at least once to the Avantgarde Acoustic UNOs because it's a helluva lot of fun to find out the truth - about horns.

I had my first encounter with horn loudspeakers about 20 years ago when, in a Munich dealer's showroom, a pair of ACR corner horns caught my eye. Although the sales person probably realized that I did not qualify as a potential customer, he quickly played the speakers for me - actually just a few second to be precise. An ear-splittng 'bang' startled me as the dealer leaned back with a grin and ended the audition of the Waltz Explosion by Richard Strauss.

With this demo, everything became clear. Even though the violins were not free of colorations, the ultimate intensity and explosive power of this horn system made a lasting impression. Compared to these dynamics, many High-End systems heard subsequently were nothing but a nice try.

At about the same time, a fateful encounter with horn speakers changed the life of Holger Fromme, founder of Avantgarde Acoustic. Hugely impressed by the dynamics and scale heard during a live Pink Floyd concert, he purchased his first corner horn loudspeaker system. It wasn't long before a search for bigger and better drivers led to his meeting with Matthias Ruff, a like-minded horn fanatic. Together, they designed their first plaster molds for producing various spherical horns. Today Avantgarde's internationally admired spherical horns are made by injecting molten plastic at pressures of up to 2,500 toms into 8-ton steel molds.

A short history lesson now. It was over 100 years ago that the gramophone, the first mechanical horn speaker, was presented to the public. Then came the 'horn pioneers', men like Paul Klipsch and Paul Voigt, who prepared the way for the 'Golden Age' of high-efficiency horns. But the triumphant advances of powerful transistor amps some decades later put an end to the big horn era. - vanquished by progress or so it seemed.

As with so many other 'old' technologies, the reported death of horns may have been announced prematurely. Black vinyl is still rotating, tube amps find passionate admirers and well designed horn system continue to fascinate well into the future. Speaking of well-designed: our ears function like horns, as 'pressure transformers' that gradually decrease their diameter from the outer ear through the auditory canal to amplify sound pressure at the actual ear drum. Thus, precisely designed and calculated horns have capabilities far beyond what regular speaker could ever hope to achieve.

The 100dB-per-watt sensitivity of the UNO, the smallest of the Avantgarde Acoustic horn systems, only partially explains why this speaker transforms a music signal into such intense, spine-tingling soundwaves. Speed and acceleration, two forces which govern how musical notes swell and decay, also play a major role. An efficient horn reduces the driver membrane excursion by a factor of about 10. For the same sound pressure level, a conventional speaker cone has to build up 10 times the speed, requiring 100 times the amplifier power!

Hand in hand with these effortless dynamics comes a virtual increase in effective membrane area, with midrange and tweeter diaphragms performing like 20 and 50cm cone diameters. Spherical horns do not focus the sound as much as their exponential cousins but do concentrate the direct wave front to a far higher degree than conventional loudspeakers. This gives an immediate impression of precision, which dominates the performance of these designs even in difficult acoustic environments.

Horns work like magnifying glasses, both in the positive as well as negative sense. The smallest errors in design or execution are mercilessly revelealed as though served on a silver tray. In the past, poorly designed horns were responsible for bringing discredit to the entire species. For this reason, Avantgarde Acoustic points at the precision offered by their ABS injection-molding technique. Their steel modls are manufactured to a tolerance of 5/100mm. Both Matthias Ruff and Holger Fromme prefer spherical horns which, contrary to exponentional ones, do not focus high frequencies more strongly than low frequencies. This frequency-balanced performance leads to a surprisingly high degree of freedom where to site and adjust the horns relative to the listening position.

Although easily achieved by increasing the drivers' compression ratio, Avantgarde Acoustic purposely eschews increasing the UNO's sensitivity beyond the level where harmonic distortion beings to rise. This is exactly this reason why most PA systems, tuned for high output, are unfit for HiFi applications. By design, the UNO midrange compression chamber acts as an acoustical filter, which in conjunction with the mechanical driver rolloff results in a 12dB/octave low pass filter. This allows the 10cm midrange cone to be driven without any passive network components in its signal path. Merely the tweeter requires a simple 1st order crossover.

Below 220Hz, the low-mid frequency horn yields to the laws of Physics. Only corner horns that use the listening room sidewalls as an extension of their throat area are capable of reproducing truly low bass. Dedicated low-bass horns require horns roughly the size of mobile homes. Due to their uneven frequency response, phase shifts and rather limited low frequency extension, folded bass horns were never really considered by the Avantgarde Acoustic engineers. While earlier UNO models used a double-tuned subwoofer, Avantgarde Acoustic has now come up with a far more innovative and elegant approach. Extremely powerful PA drivers, working according to the principles of negative impedance, extend to an incredibly low 22Hz. Output and crossover matching to the horns is achieved via active control electronics. While not a horn, the four treated paper cone woofers, each 26cm [10 inche] in diameter, provide cone area and spead far in excess of most HiFi speakers.

To dive into the world of horns, you only need a few -- preferably 'quiet' -- watts without hiss or hum. The SET integrated tube amplifier VAIC VALVE 300B-SE is a good example. Allow a little space, say two to three meters between UNO and listener, then let them sing. I was immediately captivated by the character and charisma of the UNO. A slightly far-fetched comparison comes to mind. I put on a live recording of five Pop Divas as recently released by Epic Music VIdeo on the "Divas Live" DVD. Is it that Dolby Digital makes the vocalists -- including Mariah Carey -- sound as though they're having to work too hard? Probably not since this changed the very moment Aretha Franklin walks onto stage and completely dominates the proceedings.

Compared to this lady's powerful stage presence, Mariah Carey possesses rather little. The same thing happened with the new UNO. They control and capture the entire room, filling it with music as though the artists were paying you a personal visit. I found pure a capella vocals, Gospel and chorus pieces to be especially thrilling, and without any trace of 'horn-type' colorations.

Change of program - I put on old rather un-spectacular and truly poorly recorded rock CDs. Once again the UNO surprised with dynamics and power very hard to credit as deriving form the aged recordings. What the UNO delivers from non-aduiphile tracks is truly spectacular.

In the meantime, I almost forgot that the UNO was still hooked up to the first CD/DVD player that I could lay my hands on in order to break-in these speakers. With excellent electronics, even average speakers can sound rather decent due to the quality signal they receive. With the UNO, a similar thing happened, but in reverse. This uncritical 8-ohm speaker load elicited undreamt-of sounds from even quite modest electronics. The UNO is not some Diva demanding 100,000 Deutsch Marks worth of amplification to really sing.

Of course this didn't mean that swapping just any old DVD player to a Linn Mimik did not improve the sound. What a revelation. That average DVD players in 2-channel mode have nothing to do with High End was made blatantly clear by the UNO's 'acoustical magnifying glass'. Still, the listening sessions never descended into small-minded 'hear the grass grow' controversy or concerns, about the air betweent the 3rd and 4th violin, just as in a concert hall these 'elementary' points never ever cross my mind.

The UNO fascinated in a different way then. Imagine you are not really a John Fogerty fan bur were nevertheless present during the live recording of his album Premonition. Fogerty and drummer Kenny Aronoff would still have carried you away with the rest of the audience. And that's what happened to me with the Avantgarde Acoustic horns. Regardless of my individual preferences, and independant of musical styles, the UNO presented exactly what music is essentially all about: drive, tangible emotions, crackling tension and authenticity.

Perhaps you require more than just massive dynamics and ultra-low bass? Perhaps you prefer to relish in the finest of tonal colors and nuanced shadings while being carried aloft in clouds of sound? No problem, since the UNO is neither an uncouth brute nor a two-trick pony. The natural tonal balance of instruments, not only tubas or bass, is sensitively and accurately conveyed. And the three-dimensional soundstage is incredibly big and exciting. Some people may point out that background noises and ambient reflections off the recording venue's walls could be rendered with more depth, or that voices and instruments are bigger than usual. And both are correct. Without a doubt, the acoustical stage feels mightier, larger and more dramatic than what one is used to with small speakers. So what? I can live with that. In fact, it's one of the reaons why I love the Avantgarde Acoustic UNO so much.

In summary, combined with one of the best actively controlled and integrated subwoofers, this smallest horn speaker from Avantgarde Acoustic jumpstarts the party: powerful, mighty and incredibly dynamic, the UNO transfers a few watts of (tube?) amp power into massive listening fun. The open and uncolored horn speakers here give lie to the critics. Listened to at the appropriate distance, they provide an overwhelming listening experience - a magical transducer that demonstrates all of the fascinating qualities of big horn speakers at their most impressive.

Owners of good record collections, beware! Exteme danger of addiction!

Udo Ratai, Image HiFi, Germany, Issue 5/1999