Avantgarde Acoustic - Horntechnologie


DATE: 1999-05-01

Test review by Udo Ratai (Image Hifi, Germany, Issue 5/1999).

Horn loudspeakers were born at a time when (tube)amplifier watts were rare. Today the opposite often applies, with monstrous amplifiers and  thick as your arm  speaker cables driving low-sensitive High-End monitors. Has the world turned upside-down? Horn loudspeakers rock the foundation of people´s ideology: you either love them or hate them - horn loudspeakers have their frantical disciples as well as their unconvinced critics. The latter should listen once to the Avantgarde Acoustic UNO´s, because it sa hell of a lot of fun to find out the truth about horns.

I had my first encounter with horn loudspeakers about twenty years ago, when in a Munich dealer sshowroom, a pair of ACR corner horns caught my eye. Although the salesperson probably realized that I did not qualify as a potential customer, he quickly played the speakers for me. Actually just a few seconds, to be precise. An ear-splitting  bang  startled me as the dealer leaned back with a smile and ended the audition of the Waltz Explosion of 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 more than 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 of a live Pink Floyd concert, he purchased his first corner horn loudspeaker system for his own use. It wasnt long before a search for bigger and better drivers led to his meeting Matthias Ruff - a like-minded horn lunatic. Together, they designed their first plaster molds for producing various spherical horns. Today Avantgarde sinternationally recognized spherical horns are made by injecting molten plastic at pressures up to 2.500 tons into 8 ton steel molds.

A short history lesson. 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 advance of powerful transistor amps some decades later put an end to the big horn era. Vanquished by progress, or so it seemed.

Like many other  old  technologies, the reported death of horns may have been exaggerated. Black vinyl is still rotating, tube amps find passionate admirers and well designed horn systems will fascinate well into the future. Speaking of  well designed ; our ears are like horns,  pressure transformers  that gradually decrease their diameter from the outer ear through the auditory canal to amplify sound pressure at the eardrum. Thus precisely designed and calculated horns have capabilities way beyond what normal speakers can ever achieve. The 100dB per watt sensitivity of the UNO, 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, forces which govern how the musical tones swell and decay, also play a major role. An efficient horn reduces the driver membrane excursion by a factor of around 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 50 cm diaphragms. Spherical horns do not beam the sound as much as their exponential cousins, but concentrate the direct wavefront to a far higher degree than normal loudspeakers. This gives an immediate impression of precision, which dominates the performance of these loudspeakers, even in difficult acoustic environments. Horns work like magnifying glasses, in both the positive as well the negative sense. The smallest mistakes in design or execution are mercilessly revealed and served on a silver tray. In the past, badly designed horns were responsible for bringing the whole species into disrepute. For this reason Avantgarde Acoustic swears by the precision offered by their ABS injection molding technique; their steel molds are manufactured to a tolerance of 5/100 mm. Both Matthias Ruff and Holger Fromme prefer spherical horns which, contrary to exponential horns, do not beam high frequencies more strongly than low frequencies. This balanced performance leads to a surprisingly high degree of freedom in positioning and adjusting the horns, relative to the listening position.

Although easily achievable by increasing the compression ratio of the drivers, Avantgarde Acoustic purposely avoided increasing the sensitivity of the Uno beyond the level where harmonic distortion also begins to rise. It is for exactly this reason that many PA systems, tuned as they are for high output, are not suitable for Hifi applications. By design, the UNO midrange compression chamber acts like an acoustical filter, which in conjunction with the natural roll-off of the driver results in a 12dB low pass filter, allowing the 10cm midrange cone to be driven without any passive crossover components in the signal path. Only the tweeter requires a simple, first order crossover.

Below 220 Hz, the low-mid frequency horn yields to the laws of physics. Only corner horns, which use listening room sidewalls as a trick to enlarge the horn mouth area are capable of propducing - really low bass. Low-bass horns require horn mouth areas roughly the size of a mobile home. Due to their uneven frequency characteristics, phase shifts and rather limited low frequency extension, folded bass horns were never really considered by Avantgarde Acoustic. 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 down to an incredibly low 22 Hz. Matching of volume and crossover frequency with the horns is achieved via the subwoofers active control electronics. Sure its not a horn, but the four treated paper cones, each 10 inch (26 cm) in diameter, provide driver area and speed far beyond that of most hifi speakers.
To dive into the world of horns you only need a couple of watts, preferably  quite  watts, without hiss or hum. The single-ended integrated tube amplifier VAIC VALVE 300B-SE is a good example. Allow a little space, say two to three meters between the UNO and the listener then let them sing. Immediately I was caught by the character and captivating charisma of the UNO. A slightly far-fetched comparison comes to mind. I put on a live recording of five Pop divas, recently released by Epic Music Video on the  Divas Live  DVD. Is it the Dolby-Digital sound that makes the vocalists, including Mariah Carey - sound like they\\\'re having to work hard? Probably not, because this changes the moment Aretha Franklin walks onto the stage and completely dominates the procedings. This lady has a powerful live-presence, Mariah Carey, in comparison, very little. The same thing happened with the new UNO. They control and capture the total room, filling it with music, as though the artists were paying you a visit. I found pure  a capella  vocals, gospel and chorus pieces to be especially thrilling, without a trace of any  horn type  colorations. Change of program; I put on old, rather unspectacular and really badly recorded Rock-CD´s. Once again the UNO surprises with dynamics and power hard to credit as coming from these aged recordings. And what the UNO gets out of non-audiophile 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 burn-in the speakers. With excellent electronics, even average speakers can sound good, due to the quality of the signal they recieve. With the UNO, a similar thing happens, but at the other end of the hi-fi chain. The uncritical 8-Ohm speaker load elicits undreamt-of tones from even quite modest electronics. The UNO is not some diva which needs a hundred thousand Deutschmarks worth of amplification to sound good. This does not mean that swapping from just any old DVD player to a Linn Mimik did no improve the sound. What a revelation! That average DVD players in stereo mode have nothing to do with High End is made extremely clear by the UNO  acoustical magnifying glass . But the listening session never descended into small-minded  hear-the-grass-grow  controversy or discussions about the air between the third and the fourth violin. Because in a concert hall these  elementary  points as well never ever cross my mind. The UNO fascinated in a different way. Imagine you are not really a John Fogerty fan but were nevertheless present during the live recording of his album  Premonitition . Fogerty and his drummer Kenny Aronoff would still have managed to carry you away with the rest of the audience. That´s what happened to me with the Avantgarde Acoustic horns. Regardless of individual preferences and independent of music styles, the UNO presents exactly what music is essentially all about: drive, tangible emotions, crackling tension and authenticity.

Perhaps you are not happy with just massive dynamics and fundamental deep bass alone?. Maybe you prefer to relish the finest tonal colors and shadings while being carried away on clouds of sound? No problem. Because the UNO is neither uncouth nor two dimensional. The natural tonal balance of instruments, not only the tubas or brass, is sensitively and accurately reproduced. And the three-dimensional soundstage is incredibly big and exciting. Some people may point out that background noises and reflections from the recording venue swalls could have more depth and that voices or instruments are bigger than usual. Both are correct. Without any 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 its one of the reasons I love the Avantgarde Acoustic UNO´s so much.

In combination with one of the best actively controlled subwoofers, the smallest horn loudspeaker from Avantgarde Acoustic gets the party going: powerful, mighty and incredibly dynamic, the UNO transfers a few watts of (tube-) amp power into sheer listening fun. The open and uncolored horn speakers give lie to the critics and at the right distance, provide an overwhelming listening experience. A magical transducer which demonstrates all the fascinating qualities of big horn systems most impressively.  Owners of good record collections beware! Extreme danger of addiction!

Review by: Udo Ratai Image Hifi, Germany Issue 5/1999