Gramophone Dreams #71: Heretic AD614 loudspeaker

Herb at the HiFi Loft. (Photo: Jason Tavares)

I remember a Saturday morning around 30 years ago, when I just happened to be at Sound by Singer, the New York City audio salon, watching this wizardy German fella named Joachim Gerhard unbox the newest speaker in his line, Audio Physic. I remember how bright the sun was as it streamed in through the windows, forming a wall of light behind him and silhouetting two implausibly thin box speakers. Their silhouetted forms displayed proportions similar to the World Trade Center.

I was taken aback by how Gerhard set up these thin twin towers in Andy Singer’s biggest listening room. He positioned both speakers at least 6′ from the wall behind them and maybe 5′ from the walls beside them, with at least 10, maybe even 12 or 13′ between them, radically toed-in. Andy’s listening chair had been moved into the middle of the room—closer to the speakers than to the wall behind it. I had never seen small speakers set up in a way that so dominated an entire room.

Speaking in the serious tones of a German scientist, Gerhard explained how, with “conventional speakers,” front-baffle–instigated response anomalies (diffraction) obscure detail and remind listeners constantly of the speaker box’s presence, and how “applied physics” has allowed his “baffle-less” designs to eliminate that problem and reproduce the “fine details” and “intricate soundstaging” that conventional speakers could not.

Everyone in the room agreed: Joachim Gerhard’s speakers disappeared more completely than any we had ever heard. When I sat alone in the sweet-spot chair, I watched the well-drawn outlines of musicians performing in the space between the speakers, without directly noticing the speaker boxes themselves.

This was my dramatic introduction to a new type of carefully conceived audio holography, where the projected soundspaces were clearer, wider, and more conspicuously arranged than I ever thought possible. Unfortunately, the musical part of the program came through affectless and low on corporeality.

Since that Saturday at Sound by Singer, such narrow-baffled speakers have become de rigueur in high-quality audio. This design orthodoxy dominates the marketplace so strongly that it has incentivized conformity and marginalized competing engineering strategies. How many newly designed horns, omnidirectional, electrostatic, planar-magnetic, or full-range open-baffle speakers do you see advertised these days? The hegemony of the skinny-box orthodoxy had me worrying about our collective music-listening future—until a day in September 2022 at Jason Tavares’s elegantly appointed HiFi Loft in Hell’s Kitchen, NYC, where, after auditioning Klipsch’s new, spectacularly dynamic, precise-imaging Jubilee horns (which have front baffles 52″ wide) and Harbeth’s latest not-skinny-but-consummately-coherent SHL5plus XD, I auditioned these stout, unpainted, unveneered-plywood box speakers. Their 19″-wide baffles looked ever so much like the baffles on Altec’s 612 utility enclosures, which I once used with my 15″ Altec 604B coaxial speakers.

Jason played Frank Sinatra Sings for Only the Lonely (Capital LP W-1053) on Luxman’s upgraded PD-151 MARK II turntable (see Michael Trei’s review in the March 2023 Stereophile) with a Dynavector XX2 moving coil cartridge (covered in the March 2023 Gramophone Dreams). For the first time since I can’t remember when, Sinatra seemed to be standing intensely there in front of me, sounding like his warm-blooded, coolness-emitting self and not a ghostly hologram.


The speakers I was listening to were the smallest of Heretic Loudspeaker Company’s three models, the $7290/pair AD614 (footnote 1); they placed Frank between the speakers more physically than I’d ever heard in an audio store. While I smirked with pleasure, I began wondering if this might be the loudspeaker—or at least the type of loudspeaker—I’d been searching for.

These Heretic speakers, Jason said, were manufactured in Montreal, Canada. Their coaxial drivers were made in Italy by a company called Faital Pro. From one look at their raw-looking cabinets, it was obvious that Heretic’s founder and chief engineer, Robert Gaboury, created the AD614 in willful contradiction of every protocol of today’s speaker-design orthodoxy. The AD614 was not designed to look or sound or sit in your room like any speaker currently listed in Stereophile‘s Recommended Components.

The AD614 uses a 12″ coaxial driver rated at 97dB/2.83V/m into 8 ohms. This pro-quality driver features a cast basket, which supports a treated-paper cone with a “triple-rolled” surround, a glass-fiber voice-coil former, and a ferrite magnet. Partially visible behind its open-weave dustcap sits a compression-driver tweeter with a neodymium magnet, which pressurizes a short, thick aluminum horn with a dome made of polyether ether ketone (PEEK) plastic.

According to Gaboury, “One very important aspect is the tuning of the AD614’s box. I started out by back-engineering the Altec 612 Utility cabinet, which was designed 20 or 30 years before Thiele/Small parameters were commonly used to calculate air volume and tuning, so Altec’s box was probably tuned by ear.

“The first aspect I found puzzling was the ductless vent, with no ‘tube’ to tune the port. Altec’s ‘port’ works in the same manner as any other bass-reflex design, except the loading is not centered on a single, precise frequency but rather over almost a whole octave, because—my hypothesis—it does not work radially. Air pressure can escape naturally, from all angles, thereby extending loading a bit. “It also has an effect on impedance by reducing the common saddle curve, so electrically the AD614 looks more like an infinite baffle design.”

According to Gaboury, the AD614’s drivers are connected through a series-wired second-order Linkwitz-Riley crossover terminated at the solid copper binding posts (footnote 2). “Recommended amplifier power: 3–300W, unclipped.” These boxes can play LOUD!

According to Heretic’s website, “Most of today’s loudspeakers have a circuit called a Baffle Step Compensation (BSC) filter, which boosts low frequencies to compensate for the acoustic effects created by narrow enclosures. Heretic speakers do not have this circuit and therefore rely on the ‘broad shoulders’ of the enclosure, acting as a launch pad for low frequencies.

Therefore, it is advisable to place Heretic speakers against the wall and benefit from the natural reinforcement offered by your room boundaries.” How’s that for heresy?

Guess what the “AD” in AD614 stands for? Like me and all my pals, Robert is a dedicated fan of the eager, aw-shucks sincerity, snarky-but-light-hearted humor, and timeless audio wisdom dispensed by the late Art Dudley. Robert explains: “I met Mr. Dudley a few times at shows, and I was always torn between telling him how much I liked his writings and bias toward a certain type of sound—emotions, really—and just keeping to myself, which I did.

“When he passed away, I thought that maybe, maybe I should have told him, but then again, who am I?

“I think Mr. Dudley was the ultimate heretic, and the ultimate gentleman. I felt he didn’t care much for the business side of hi-fi and was absolutely solid and true to his convictions.”

In my mind, Art was the high priest of an audiophile cult that believed that listening was a true path to the Divine.

The design

During my years, I’ve noticed that concentric drivers seem to project singers into the room with a greater presence than domes and cones mounted separately. And that big-coned concentric drivers, like 15″ Altec and Tannoy coaxials, project voices and instruments with greater ease and presence than smaller ones. You tell me, how can any speaker effectively imitate a chesty baritone, a grand piano, or a close-miked cello with a 5″ driver?

Gaboury says: “In the frequency domain, coaxial (point source) drivers are everything but linear. In the time domain, they are excellent. But large paper woofers do not act like the theoretical ideal piston. Paper has too much flexibility, and by the time higher frequencies reach the outside perimeter of the cone, they are already out of phase and damped by the cone’s compliance. Yet, we must question whether pistonic behavior is musically relevant or not. Or could controlled cone breakup become desirable musically? I think it can.” That’s pretty heretical. Right?

My friend David Chesky and I believe that humans are way more sensitive to distortion and timing than frequency response, and that the majority of today’s box speakers create their own “signature” time smear that we can hear but don’t notice—except when it’s not there. Like when listening with headphones.

According to Gaboury, the main speaker-design question is always “Should speaker designers focus on the frequency domain or the time domain?” He thinks the time domain should be prioritized. And I agree.

I queried Gaboury about the AD614’s crossover.

“Why Linkwitz-Riley? Because it sums to zero. Because the woofer and tweeter are connected in series, the network logic is inverted. If you want to fix something in the high frequencies, you must act on the LF section. It’s like writing with your left hand in front of a mirror.

“Why second-order? Because I cross at 1.7kHz, which is a bit under the point where the tweeter starts to feel uncomfortable. I also chose that frequency because this is where the dispersion of both drivers overlaps nicely, while steering away from the woofer cone’s breakup.”

I asked J.C. Morrison, me ol’ runnin’ buddy and audio-engineering mentor, if he had any thoughts about a two-way coaxial driver with a series-implemented Linkwitz-Riley crossover. His response:

“Parallel crossovers store energy and release it in a different way than series crossovers do. Because all the current goes through both drivers and the filter components shunt current ‘sideways,’ the drivers are forced to act more as one. In parallel, the drivers act alone. If the source is current drive, then a series 2-way crossover is the ‘constant voltage’ model and much less affected by motional impedance than a parallel crossover. This is why series crossovers favor the higher output impedance of no-feedback tube amps and/or current drive.”

Gaboury: “Another aspect that tickled my mind was that serial crossovers are almost impossible to model in software, which is probably the reason nobody is crazy enough to dig into them. Designing a second-order serial crossover is something that, to do right, requires a lot of time spent doing trial-and-error listening. That amount of time, plus the uncertainties involved, cannot be justified in a mainstream corporate environment.”

According to Heretic’s published specs, the AD614 comes in a 3ft3, 12-ply, FSC-certified birch plywood box that weighs 43lb and measures 25.5″ high, 18.75″ wide, and 14.5″ deep. That’s the same size and weight as Altec’s classic 614 speaker enclosure, which was used with Altec’s own 12″ coaxials. Finishes for Heretic speakers are specified as a choice of water-based acrylic Black or a semitransparent mixture of linseed oil and bee’s wax in either White or Clear. Heretic’s warranty lasts 10 years.

Footnote 1: Heretic Loudspeakers, c/o Robert Gaboury, 9320 Saint-Laurent Montreal, Quebec CANADA H2N 1N7 Tel: (438) 404-7056. Email: hereticloudspeakers@gmail.com Web: thehereticspeaker.com. US importer: Fidelis Distribution, 460 Amherst St., Nashua, NH 03063. Tel: (603) 880-4434. Email: sales@fidelisdistribution.com Web: fidelisdistribution.com

Footnote 2: See ranecommercial.com/legacy/pdf/ranenotes/Linkwitz_Riley_Crossovers_Primer.pdf.

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