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: Web:

Footnote 2: See


JRT's picture

Herb Reichert mentioned the use of 2nd order Linkwitz-Riley passive series crossovers.

Linkwitz-Riley refers to the late greats Siegfried Linkwitz and Russ Riley. You might find interesting some of Siegfried Linkwitz's commentary on the subject of passive and active crossovers, quoted excerpts below, with more available on the associated webpage from his website (links further below), which is a treasure trove of excellent information centered on the applied science and art of loudspeaker design, with much surrounding information.

"Crossovers may be implemented either as passive RLC networks, as active filters with operational amplifier circuits or with DSP engines and software. The only excuse for passive crossovers is their low cost. Their behavior changes with the signal level dependent dynamics of the drivers. They block the power amplifier from taking maximum control over the voice coil motion. They are a waste of time, if accuracy of reproduction is the goal."

"I have a strong preference for line level active dividing networks ahead of the power amplifiers. In this approach the power amplifier output is connected directly - except for a very low resistance speaker cable - to the voice coil of the driver. The amplifier takes maximum control over the motion of the speaker cone which gives a greater sense of clarity and dynamism compared to a passive dividing network between amplifier and driver. Active crossovers make much more effective use of amplifier power. A clipping woofer amplifier is not seen by the tweeter, which has its own amplifier. The clipping of the woofer amplifier may not even be noticed in this case. It would surely be heard with a passive crossover, where it might even overheat and damage the tweeter, because of the large amount of high frequency energy in the clipped signal."

"Crossover filters for a speaker usually incorporate frequency response corrections for the individual drivers to obtain a desired overall response. The active network has the advantage of correcting easily for different sensitivities of drivers and equalizing not only the individual drivers but the combined response as well. Not having to deal with the interaction between driver impedance and passive filter network gives the designer of an active crossover/equalizer much greater freedom and control to develop a superior product."

Jonti's picture

Fascinating stuff as always, Herb. I recently picked up a pair of Altec 614D enclosures housing archaic 600B 12-inch full-range drivers. The "puzzling ductless vent, with no 'tube' to tune the port" that Gaboury describes is there on the 614D too, and left me equally mystified, but I like the broad-spectrum effect it has on the tunefulness of the bass. The really surprising thing for me is how well-defined the lower frequencies are coming through such a port. Vastly superior, to my ear, to the arm's-length cylindrical tubes used in Tannoy Arden ports, for example.

Having placed the Altecs a fair distance away from the back wall by instinct, I'm now going to try pushing them closer to see if there's any audible benefit in doing so.

Ortofan's picture

... he could live happily ever after with a pair of Spendor BC1 speakers?

If that was the case, why, then, is the "bunker" not home to one or the other iteration of the Harbeth SHL5plus - or, for that matter, the Graham LS8/1 or the Stirling Broadcast LS3/6?

However, if he has since developed an affinity for speakers with coaxial drivers and paper cones, then he really ought to do a follow-up review of the MoFi SourcePoint 10.

Lastly, it should be noted that, toward the end of his career, the late Bud Fried was a proponent of series crossover networks.

Simon from Oz's picture

Sorry Herb, that chair is not a Le Corbusier piece. It was designed by Marcel Breuer in 1925, often called a Wassily Chair as he also made one for the artist Kandinsky.

Le Corbusier did some beautiful sofa and chair designs, but that's not one of them.

thethanimal's picture

Simon, I initially thought that was a mistake too, but realized the Le Corbusier chair was at his Sound by Singer demo of Audio Physic speakers some time ago, while the lead picture is from a Heretic demo at HiFi Loft. Different salons, different times, different chairs, but good taste all around.

Simon from Oz's picture

Ah ok, I should pay attention more. Thought it was a glaring error, bit like saying that First Watt amp was a Dan D'Agostino design...

tenorman's picture

Such a lovely and well deserved tribute by Heretic speakers of Montreal to Art Dudley . Incorporating Art’s initials into the name of their speakers was a very kind gesture .

Beautifully wrriten review Herb - thank you . I particularly enjoyed ( and chuckled at ) your wonderful “ Webb Telescope vividosity” descriptive . A classic Herb-ism if there ever was one .Doesn’t get better then that . Unfortunately, the Heretic’s are more than a little out of my price range . Thankfully I have my beloved Falcon Ls35a Gold Badges which regularly bring me joy .

Herb Reichert's picture

I am pleased you enjoyed it and honored by your observations.

Art Dudley's stories made us all better Listeners.


Long-time listener's picture

"I could always hear the paper in the Heretics' cones, and I was never not aware of the location, mass, and volume of their thin-walled boxes."

Those sound like problems with tonality. Is that not a problem?

I once heard those Audiophysic speakers you spoke of -- I assume it was the same one -- and the memory has stayed with me for decades. I've always regretted not buying them. Surprised to hear them spoken of so disparagingly.

Trevor_Bartram's picture

The use of large diameter cone coaxial driver on a large baffle is a way of mitigating baffle step compensation and edge diffraction. The large cone acts as a horn to control directionality at high frequencies where diffraction in a small driver is problematic. However the large cone is moving and causes doppler distortion at high frequencies. I'm unsure if Doppler distortion is audible but it should be measurable. Heretic should submit their speakers to a Stereophile review!

Trevor_Bartram's picture

Herb, with a 12" paper cone operating to 1.7KHz, did you hear any cone breakup? Any coarseness to vocals? There are good reasons why various alternate cone materials (bextrene, polypropylene, metal etc) have been tried over the years. Some upper midrange coarseness has even been noted in Buchardt's earlier 6" paper cone designs.

Mr.Taylor.Calculus's picture

Thanks, Herb.

As always, I greatly enjoyed your column. I was, however, looking forward to hearing how it worked with your LTA Z10e integrated. Did you have any comments about that combination?

Herb Reichert's picture

I still have not hooked up the LTA Z10e to the Heretecs.

My only excuses are sloth and the Z10e is in my desktop system so I can listen to electrostatic headphones all day.

but I can't imagine how it would not work with the Heretecs

when I finally try it I will report back


RH's picture


Excellent review! I find you often get at the gist of sonic characteristics you are seeking, and convey them well to the reader.
For instance in your older review of the Joseph Audio Pulsar speakers, you nailed the difference from the Harbeth speakers - "the extra flesh and density" in the Harbeth sound. My experience with owning both Harbeth and Joseph Audio speakers (currently the Perspectives) concur.

Like you I enjoy sonic density, flesh and blood, to the sound of a speaker. So the Devore O series speakers have been a favorite of mine for those qualities. But they were too wide and presented some ergonomic problems for my smallish room which a much narrower speaker - the Joseph Audio Perspectives - solved for me. Plus I adore the purity of tone and imaging in the Joseph speakers.

My big "discovery" was adding a smallish curved diffusor behind and between my Joseph speakers. This added a big dollop of image density and aliveness! Now sonic images of a voice, a drum kit, a sax etc just seem "there" - palpable and solid. As close to the best of both worlds - the mammoth soundstaging and imaging prowess and purity of the Joseph sound, with that added density - that I've managed to achieve thus far.

I'd love to hear these Heretic speakers (though their form factor wouldn't work for my room).

thethanimal's picture

Herb, I imagine you’ve auditioned the OJAS bookshelf speakers with the coaxial driver. It seems the two are cut from the same cloth; I’d be interested in your thoughts. Maybe an upcoming Gramophone Dreams?

Herb Reichert's picture

the OJAS bookshelf speaker.

But I suspect the secret of this speaker's success, what separates it from the co-axial cohort, is the series crossover.