Avantgarde Acoustic - Horntechnologie


DATE: 2001-09-01

Horned subjects

The mythUse your hands to make a trumpet-like embouchure around your mouth. Now talk into it: Pull over please. Put your hands where I can see them! @#*^! You nearly gave me a heart attack. Phew! Noticed though how your voice got both louder and altered its character? That’s the whole point. It proves it once and for all: Horn speakers by design are one terribly sick idea for any card-carrying audiophile to entertain either momentarily or monetarily. Horns, like hands-around-the-mouth, distort tonality and change timbre. Any fool can hear that. It’s blatantly obvious. Granted, it might be acceptable for PA roadies, sound reinforcement gigs and other head-banging lo-fi enterprises of dubious sonic morale. But, keep it bloody away from fine music systems. End of story. Horns are bad. It’s an equation even simpler than relativity. Every child with Q-tips in the bathroom can see that, right? Right!
We’ve just conveniently dissed an entire technology vis-à-vis a single primitive demonstration, peppered with a fetchingly rash -- but possibly not entirely comprehensive – deduction. Let’s slap us on the shoulder; applaud our own cleverness. Let’s overlook, too, that we’ve just fallen prey to prejudice, hearsay and pseudo knowledge. Never mind having stooped to what amounts to fake common sense and phony proof, spilled like cheap ketchup to cover up some revoltingly bad taste.

Shall we try again? Leave the ketchup for the next fellas. Take a closer look instead at what we just ordered for dinner.

Another myth?It’s about the music, remember? At least that’s what I ordered: Music, not muzak. How to tell the difference? Forget the audiophile artifacts. Holographic soundstaging. Image specificity. Stygian bass extension and monster bass slap’n’slam. Think live versus canned! What if the former meant a lousy venue and cheap-ass horrendous seats, while the latter retorted with a laser-etched sweet spot and room-tuned audiophile dream loft straight out of the Rob Report - what’s the one essential quality that distinguishes the real from the artificial?
Dynamics! Ever attempted realistic dynamic scale at home? Say we set amplifier gain such that peaks began to mimic realism. Most conventional systems begin to screech from obnoxious compression. In fact, so fast does one tend to hit the stops that the frantic grope for the remote volume-down button just barely prevents massive ear clip and outright physical discomfort. Never mind that we merely raised the nominal loudness but didn’t actually expand dynamic range. Remember that dynamic range is not a function of high average output levels –that’s being deaf – but of the maximal difference between the quietest and loudest sonic event. If you’ve ever had musicians in your living room perform at normal levels -- or perhaps even played yourself -- you know the enormous range between whisper-quiet states and explosive crests. That’s dynamic scale with maximum width. In the absence of an electronic noise floor and nuance-squashing reactive crossovers, pianissississimos remain perfectly intelligible. Conversely, even the loudest of peaks don’t turn offensive to the ears because such emphatic artistic exclamation marks simply don’t suffer dynamic compression distortion that plagues most loudspeakers. When a diva goes full throttle. When a pianist falls into the clefs from two feet up. When a flautist overblows a high note at maximum air velocity. When a trumpeteer like Maynard Ferguson breaks altitude records with vein-popping pressure. When a violinist shreds his bow or pops a string. Folks, we’re talking some serious short-term bursts of intense decibel levels! But, it’s the exhilarating and hair-raising kind, not the painful stuff of a home system going into convulsions or a PA system squawking in protest. And this goose-bumps’ emotional response -- occurring spontaneously during live events when we’re overrun with the rapid ebb and flow of crescendos and decrescendos-- is what most stereo systems fail to deliver fully. The oceanic roar of the original event is sadly diminished to a teapot tempest. Bonsai audio! Now one settles for the usual suspects of audiophile artifacts, secondary characters who fancy fat-laden French sauces to disguise the absence of any real meat. Mind you, meat can be perfectly delicious and mahvelous with a designer sauce. Ditto for pinpoint imaging and thermionic bloom when they ride on the coat tails of real-life dynamics. But a regular diet of just potatoes and gravy? I’ve you’re a red-blooded carnivore, I don’t think you’d fancy a full vegetarian conversion.

The theoretical advantages of horns, according to Lou Cipher the white paper guyFree gainHorns, by virtue of focusing their transducer’s acoustical output through a geometrically expanding physical funnel, add substantial gain to that driver. Think how a power spigot attached to a garden hose adds pressure and velocity to the water jet via mechanical compression. In a speaker, the pressure the horn applies to the moving air acoustically amplifies the driver. Hence such a driver, for the same measurable output, goes through significantly less excursion – i.e. traverses less distance -- than a conventionally naked one. For a tweeter or midrange, being pistonic mechanical devices, this makes all the difference between coasting in the sweet zone and hammering at the sweat limit. This equates to better efficiency for the horn guy who gets to the finish line with less effort and the resultant non-linearities that arise with struggling. Working smart, not hard, also means reduced power expenditure to perform the easier task. Lower caloric requirements can now either hire simpler amplifier circuits with lowered part count -- think micro-power single-stage SETs -- or become a no-brainer salary for a powerful amp on cruise control. In either case, speakers included, this easy is right approach seems rather Taoist. It insists that an absence of overt effort and stress is the natural way of all living things - except humans who make things difficult and complicated.

Controlled dispersionThankfully, the Avantgarde-USA website explains the history, theory and specific applications of their low-compression spherical – rather than exponential -- horns in great but layman’s details. This liberates me from un-Taoist efforts and pretending I had much of an engineering clue by rehashing it all in my own words. However, I want to highlight a few aspects that strike me as important enough to include in this discussion right away. Consider the controversial subject of wide dispersion. You didn’t know it was controversial? Think about it. Good off-axis response is a characteristic deemed highly desirable by followers of Floyd O’Toole’s research originally conducted at the Canadian National Research Council. It’s since been implemented in most High-End loudspeakers. Broad dispersion sprays sound in as wide a lateral angle as possible. The ear/brain mechanism can’t distinguish early reflections as a separate event and thus sums them with the original signal into a single but muddied sensory input. It amusingly tends to escape audiophiles that the cure, expensive and unsightly room treatments, are a direct consequence of this much-touted off-axis. Ever wondered why ‘philes toe-in their speakers instead of firing them straight ahead? Or why they place them so far away from room boundaries that most interior designers and spouses throw fits?

Consistent performanceAccording to Avantgarde, the special spherical shape of their precision-molded horns causes 85% of the sound to be aimed directly at the listener. Only about 15% is said to “escape” as reflection, albeit highly attenuated in output. This is just like excess peripheral spray from our earlier garden hose example that’s significantly reduced in power and speed. In theory at least, these Teutonic horn speakers should thus remain uncommonly liberated from room boundary logistics. They should sound more or less the same from room to room if the claimed controlled directivity or dispersion pattern proved factual. This of course would only be true for the horn-covered frequency spectrum. The active subwoofer module fitted with standard dynamic drivers will interact with room boundaries like any other conventional speaker. User-adjustable dials do allow tuning of subwoofer gain and cutoff frequency to help minimize these common effects.

Crossover simplicityA last technical bon-mot before we get into sonic observations: As a physical function of the horns’ throat areas, the respective drivers’ operative lower cut-off frequency falls off steeply at 18dB/octave. No electrical parts are needed, period. The upper cut-off frequency is a combined function of the drivers’ natural roll-off, a 1st order electrical network and augmentation by a small inner chamber that acts as a secondary acoustical 6dB/octave bandpass filter. Thus, an effective 12dB/octave roll-off is achieved. It electrically preserves the phase-linear benefits of a shallow slope. It further doesn’t force the drivers to operate beyond their pass band by two additional octaves, as do regular 1st order designs. Velly slick. Being German myself suddenly feels like belonging to an elite club of really smart folks.

Back to realityJest aside, the ready availability of patently colored hornspeakers speaks loudly and very efficiently about the inherent challenges involved. How to marry their very real advantages -- controlled dispersion, high efficiencies, economy of transducer excursion and concomitant low distortion figures, superior mechanical rise times and potentially huge dynamic range -- with the kind of flat frequency response and tonal honesty that audiophiles demand? Would the Avantgarde Duo’s in-room performance realize these advantages without engendering those attributes that has most audiophiles discard the entire breed as unsuitable for high fidelity? Plus, would their sheer physicality end up turning listening to them into a carnivorous mono diet: Loads of dynamic meat but no subtle vitamins or not-so-subtle veggie roughage of soundstaging magic, imaging precision and any of the other audiophile qualities we’ve come to associate with our hobby ever since?

Basic specsThe Avantgarde Duo is a dual horn actively subwoofer’d four-driver three-way speaker system with 103dB+ efficiency, a nominal 8ohm load and a claimed frequency response of 22-20,000Hz. The high-frequency horn covers an ultra wide bandwidth down to 900Hz, with the passive crossover point a full octave higher at 2,000Hz. The midrange horn extends to 170Hz where it hands off to the dual 10” subwoofer. A much lower crossover point would necessitate an unreasonably large horn length and diameter as a function of physical wavelength. The Trio’s equivalent horn diameter adds 11” just to lower the crossover point by 70 cycles! Still, the Duo’s horn covers 2nd and 3rd order low and midbass harmonics and all midrange fundamentals. This model occupies the middle position of the firm’s Uno, Duo and Trio line-up and, depending on finish, retails from $15,000 to $17,000 USD. A new dual-concentric horn-within-a-horn model dubbed the Solo was first introduced at CES 2001 and will soon augment the current mix as a center and/or rear speaker. Let’s part the curtain now and lift le baton. Lights - out!

False alarmDamn, I can’t see a thing. Where’s the remote? Ah, here. But which one is the bloody CD start button? Lights back up for a sec! Now.

The real thing