Seamlessly matching a cone subwoofer to an ultra-fast, ultra-clean, ultra-high-sensitivity horn system via conventional means is about as tough a task as you can set yourself in high-end audio. In fact, until I heard the Avantgarde Zero 1s I would’ve said it was impossible—a fool’s errand. Even the best direct-radiating cone subs will seem slightly sluggish off-the-line compared to the super-charged engine of the horn-loaded drivers. Plus, as is the case with any subwoofer, you have the extremely tricky issue of crossover slope/point to negotiate, plus the little matter of dispersion pattern, which is highly directional and relatively room-independent in a horn and (down to a certain frequency) omnidirectional and highly room-dependent in a sub.
My view of a horn system’s strengths and weaknesses has not changed much since the Trio Compact days. Oh, I’ve certainly heard great-sounding horn systems at various trade shows, including several in Munich just a few months ago. (And once again I’m not denying the unique virtues of horn-loaded drivers.) But I’ve also invariably heard traces of the “cupped hands” colorations and driver-to-driver incoherence that eventually wore me down and out when I owned the original Avantgardes. (I guess I should also note that because of the various phase, time, and frequency-response issues I’ve already mentioned and the sheer aggregate size of their wavelaunch, horn loudspeakers don’t image with great precision— nor, since they don’t disperse their sound hemispherically the way point-source direct-radiators do, do they typically soundstage “outside the box.” Although the severity of these problems depends on the design of the horn and the level it is played at, certain horns can be as much the poster children for “six-foot-wide” voices and violins and guitars as vintage planars were.)
So...it would seem that to live with a horn loudspeaker system’s great virtues you must also live with a horn loudspeaker system’s great flaws. This is certainly what I’ve believed for the past two decades. And then along came the Avantgarde Acoustics Zero 1s.
What’s different about the Zero 1s? In a word, everything.
These extremely ingenious speakers were truly designed on a blank slate. They make brilliant use of Digital Age technologies (developed for Avantgarde by Danish DSP guru Thomas Holm) to solve many of the intrinsic problems of horn loudspeakers, and in particular those issues that have been the biggest stumbling blocks for me—coherence and coloration. That they succeed in doing so to an extent I wouldn’t have believed possible (had I not heard them) is a wonderment. It is also, I confess, the best argument I’ve yet come across for using DSP to optimize the performance of a transducer.
What exactly are Zero 1s? They are compact, self-powered (active), high-sensitivity (104dB/1W/1m), three-way loudspeakers with a spherical-horn-loaded tweeter, a spherical-horn-loaded midrange, and a direct-radiating cone woofer. All three drivers are housed in a stunning Bauhaus-like enclosure made of a sandwich of polyurethane foams—one of the coolest-looking objects of audio art I’ve seen since, well, the Avantgarde Trios. Why did Avantgarde use this foam-sandwich material? Because the random distribution of randomly-sized bubbles in the center section of the sandwich makes the entire structure highly non-resonant and self-damping, plus these plastics can be injected-molded to order, which is precisely what Avantgarde does. Internal bracing is cast into the front and rear casings of the Zero 1 enclosures, while the spherical horns are molded into the baffle, recessed into it in concave fashion, rather than projecting out in front of it. (Polyurethane’s ultra-smooth, non-resonant surfaces make an excellent material for a horn, where smoothness, particularly in the throat area, is essential to help prevent turbulence and distortion.)
Each of the Zero 1’s three drivers is powered by its own built-in amplifier. Both the tweeter and the midrange use 50W, zero-negative-feedback, Class A solid-state amps, the power supplies of which are identical to the power supply in Avantgarde’s flagship XA amplifier. A 400W Class D amplifier is used to power the woofer. (The amps were designed by Avantgarde’s resident engineering genius, Matthias Ruff.) All of the amplifiers are directly connected to the drivers’ voice coils, without any power-robbing, phase-shifting, passive crossover parts (resistors, coils, caps) in the signal path.
How do you eliminate crossovers in a three-way loudspeaker? Well, that brings us to the niftiest part of this incredibly nifty loudspeaker. As previously noted, Avantgarde commissioned Thomas Holm to develop a digital crossover network using 66-bit FPGAs (Field-Programmable Gate Arrays—essentially computer chips that are designed and programmed to order)— and FIR (Finite Impulse Response) algorithms to optimize the entire speaker’s amplitude, impulse, and phase response from about 30Hz (the cutoff frequency of the woofer) to about 20kHz (the cutoff frequency of the tweeter) within a “listening bubble” of about 2m to 4m, with a listening position of approximately 3m being ideal. (A digital crossover is capable of complex, progressive slopes running from 6dB/octave at crossover to 100dB/octave at a driver’s cut-off point; an analog X/O simply couldn’t manage this.)
The “price” of all this digital optimization is that you have to come into the Zero 1 via digital or digitized sources, which, after DSP filtration, are converted to analog just ahead of the power amplifiers via three 24-bit/352.8kHz Burr-Brown DACs. The speakers (well one speaker—for which see the sidebar on setup) come with a wide variety of digital inputs (one USB, one TosLink, two SPDIF, and one AES/EBU), all of which (save for the USB) are capable of handling 24-bit/192kHz high-resolution music files. (No—the Zero 1 won’t do DSD or double-DSD... yet.) The Zero 1 can also be sourced wirelessly via AirPort Express and offers the option of an A-to-D converter board for those of you (like me) who want to play back LPs or tapes.
With amplification built in, all you have to add to the Zero 1s to make them play is a source and a USB or AES/EBU or SPDIF or TosLink cable. (And you don’t even have to add a cable if you choose to source them via an AirPort Express.)
Provided that the speaker’s rake angle (which affects the height and directivity of the tweeter), distance from the rear wall, and toe-in are set properly (for which, see “Setting Up the Avantgarde Zero 1s”), Avantgarde claims that the Zero 1s will be virtually plug ’n’ play in any room, doing their DSP-optimized magic regardless of the listening room’s shape or size or damping. (Remember that because of their intense directionality horn-loaded drivers don’t excite room nodes like wide-dispersion point-source drivers, although conventional woofers, such as the one in the Zero 1, can and do.)
To test Avantgarde’s bold claim, as soon as they arrived I plopped the Zero 1s down in my living room—an irregularly-shaped space with fourteen-foot ceilings and no room treatment of any kind (I never listen in this room). After attaching their bases and fiddling with the Zero 1s’ rake, toe-in, and location vis-à-vis the rearwall as per the instruction manual, I started playing music via a Mac computer connected to Berkeley Audio’s superb USB-to-AES converter. To my amazement—and that of my wife Kathy, who, even after all these years, is the least-audiophile person I know—the sound was remarkable. To top this off, Kathy was so smitten by the incredibly cool way these things look that she asked me to return them to the living room after testing, so she can listen to them on a regular basis (unbelievable!).
Before I start dissecting the Zero 1s’ sonics, let me make two things clear. First, while the Zero 1s sounded far, far better than any speaker had any right to do in the totally untreated space of my living room, all speakers—including horns—will perform more optimally in a room that, either inherently or by design, has a judicious mix of damped and “live” surfaces. Second, though the Avantgarde Zero 1s have been DSP’d to sound amplitude/ impulse/phase-correct within a spacious listening bubble, their response is not intended to be further tailored to a given room via the DSP built into the speakers or by an outboard DSP unit—nor does Avantgarde encourage users to try this. In Avantgarde’s opinions such manipulations will only screw up an already painstakingly optimized sound, and whatever “gains” may be heard in certain areas will most certainly be traded off against profound losses in others.
So...what does the Zero 1 sound like?
I could say, “Like an electrostat with sensational dynamic range, limitless loudness capabilities, and deep, superbly defined bass.” But that would be a bit misleading, as ’stats have more soundstage depth than the Zero 1s, somewhat higher resolution, and less midrange presence; plus, most of them are warmer in timbre, particularly in the midbass, where they usually have a hump, and the presence range, where they’re usually recessed. What the Zero 1s really sound like is precisely what they are: horn loudspeakers without the horn-loudspeaker colorations.