This almost happened 13 years ago. Thinking the time was right for a Klipschorn review2006 was the 60th anniversary of its designI got in touch with a Klipsch representative, who requested photos of my room and details of its size and construction style. My reply was followed by a three-day lag in correspondence, after which came the disappointing news: "We're sorry: It won't work." The problem: There were baseboard radiators too near the corners of the room where the speakers would be installed; consequently, the Klipschorns couldn't be snugged all the way against those corner wallsan iron-clad requirement for their use.

I was disappointed but impressed; my contact at Klipsch, who was unfailingly cordial and eager to help, turned his back on a generous helping of free publicity, based on his and his company's integrity: They knew the Klipschorns wouldn't have worked as advertised in that setting. Good for them!

And now I live somewhere else.

Backstory

That old room wouldn't have worked because the Klipschorn is the rare loudspeaker whose woofer is horn-loadedyet that horn is completed by the adjacent walls of the 90-degree room corner in which it must be located. Without those surfaces, the horn is cut nearly in half. Why did they make it this way? By omitting from the original Klipschorn two very large, flat expanses of wood, designer Paul W. Klipsch was able to keep its weight down to approximately 150 lb; had it been any heavieror largersales would likely have suffered.

Why did Klipsch bother making a full-range horn at a time when more compact full-range loudspeakers were already appearing on the market? Because among all extant types of loudspeakers, a horn is by far the most efficienta characteristic Paul Klipsch defended in a 1954 interview: "Why efficiency? Well, amplifiers are cheapwe really don't need high efficiency in a loudspeaker system for the purpose of getting more horsepower output: We could just put more horsepower in from the amplifier. But when we achieve higher efficiency in the speaker, it achieves a lower distortion."

The mechanism, though difficult to perfect, is easy to understand: A loudspeaker driver is a notoriously inefficient thing, owing to a severe impedance mismatch between its diaphragm and the volume of air in the listening room; a horn acts as a transformer between the two, making it far easier for the vibrating diaphragm to get a "bite" on the air. The result is an increase in efficiency so drasticfrom approximately 1% or 2% to nearly 50% for a properly designed hornthat the diaphragm's excursions can be kept extremely low, allowing the driver to operate within its most linear range.

The first Klipschorn, which hit the market in 1947, was a two-way, single-cabinet speaker in which frequencies below 400Hz were reproduced by a 12" woofer loaded with a bidirectional folded horn, the mouth of which was, as described above, formed by the space between the Klipschorn's plywood bass cabinetry and the user's corner walls. (In use, said cabinetry was concealed from view and thus left unfinished.) Higher frequencies were reproduced by a permanent-magnet compression driver loaded with a 24"-wide exponential horn made of phenolic-impregnated wood. In the late 1950s (footnote 1), the wooden midrange horn was replaced with a new Klipsch-designed aluminum horndubbed the K400now augmented with a separate, smaller horn mounted within its mouth for the treble range; those two horns now got to share a cabinet of their own, and the bass cabinet's 12" woofer was replaced with a 15" one.

A number of running changes were made in the intervening years. During the Klipschorn's uncannily long run, its drivers have been sourced from various manufacturers, including Universal, Electro-Voice, and others. The filters comprising its crossover network were changed a few times from the gentle 6dB/octave slopes of the original two-way Klipschorn to much steeper slopes in later, three-way versions. And over the years, many small cosmetic details were altered. But according to head designer Roy Delgado, who began his career working closely alongside Paul Klipschand has now been with the company for 33 years"the Klipschorn's low-frequency horn is the one thing that has changed the least. I have modified its design only slightly, only to make it easier to build consistently well'Tab A goes into slot B' sorts of things."

According to Delgado, his ongoing work with Klipsch's five core Heritage modelsthe Heresy, the Forte, the Cornwall, the La Scala, and the Klipschornis guided by an overarching principle: "I want to do what Paul wanted, not what Roy wants."

One might safely say that recent interest in low-power tube amps has rekindled interest in those models; at the same time, the recent success of hi-fi/vinyl bars, themselves inspired by Japan's long-lived and similarly outfitted jazz cafes, has also rekindled interest in large, horn-loaded loudspeakers. One supposes this is a good time to be young, hip, and devoted to serious listening; not coincidentally, one supposes, too, that this is a good time to be Klipsch.

The company seems to think so: In September 2018, they introduced a new, easier-to-install version of the world's most long-lived commercial loudspeaker. In the new Klipschorn AK6 ($14,998/pair), the bass horn has been completed with the addition of three large MDF panels, plus additional internal bracing. Thus one can accurately describe the Klipschorn AK6, which is 45lb heavier than the standard Klipschornproduction of which has now ceasedas a corner horn that comes with its own corner.

Description

The Klipschorn AK6 is a three-way, fully horn-loaded loudspeaker of considerably greater-than-average size and sensitivity: It measures approximately 53" high by 31" wide and 28" deep, tips the scales at 220 lb each, and is said to require only 1W of power to produce a sound pressure level of 105dB, which is on a par with a jackhammer, a gas-powered chainsaw, and a five-string banjo.

Long before such observations became fashionable, Paul Klipsch was known for suggesting that the sound of music resides mostly in the midrange; for reproducing the approximately 3.25 octaves between 450Hz and 4.5kHz, the AK6 uses a compression driver with a 2" phenolic diaphragm, loaded with an exponential horn molded from rubber-impregnated ABS plastic, with a 16.5" wide by 5.5" high mouth. Installed just above that horn is a far smaller hornits mouth is 4.25" by 1.75"molded from fiberglass-impregnated ABS plastic in a Tractrix flare, driven by a compression driver with a 1" phenolic diaphragm. The midrange and treble drivers are mounted inside a 12"-tall upper cabinet, the four stiff rubber feet of which engage with recesses made for them in the top surface of the bass cabinet.

And what a bass cabinet it is! For the most part, the listener sees only a large, unblemished expanse of wood, beautifully veneered, but behind it is a front-firing 15" woofer loaded by an 8'-long exponential horn. The horn's throat begins with a comparatively narrow slotto increase pressure as well as to conform to the mathematical requirements of the horn's predetermined rate of expansionbefore directing the woofer's front wave both straight up and straight down, prior to traveling through the remainder of the horn, which is constructed with dozens of precisely cut plywood and MDF pieces. Portions of the cabinet interior are accessible via side-mounted grilleworkas with the grille for the midrange/treble cabinet, these are held in place with magnetsbehind which one sees conduits for the internal wiring, as well as the crossover's output and input connectors, respectively, for the midrange and treble driver cables and the cables from the user's amplifier.

My review pair appeared very well-made, their cherry veneervisible mostly on the front of the bass cabinet and the top of the midrange/treble cabinethaving been expertly flip-matched between the left and right speakers. I have neither the vocabulary nor the color perception to accurately describe the Klipschorn AK6's gorgeous, vintage-inspired grille fabric; suffice it to say, I never tired of gazing at these speakers, with or without a soundtrack. Their styling is as timeless as anything from Stickley, Jaguar, Rolex, or Savile Row.

Installation and setup

I'll draw the curtain of charity over my experiences receiving, unpacking, and assembling the Klipschorn AK6s: On the day they arrived, I was the only one at home, and none of my able-bodied neighbors were available to help. With rain a possibility and nightfall a certainty, I didn't have the luxury of waiting for assistance, so I worked alone, countering the speakers' considerable bulk and weight with a few 105dB outbursts of my own, none suitable for children. The worst of my profanities were directed at the flimsy and unwieldy cardboard cartons in which the bass cabinets were packed, and which are surely good for only a single ride.

Suffice it to say: Unpacking and setting up a pair of Klipschorns requires two able-bodied people and a home in which all doorways between the delivery truck and the listening room are at least 29" wide. Trust me on this.

It took about an hour and a half to get the four separate cabinets unpacked and in the door, after which things went reasonably well. I put felt sliders under the assembled speakers as an aid in positioning them and soon found that the closer they were to the corners of my room, the better these new Klipschorns sounded. This observation is corroborated in the AK6's slim owner's manual, which states: "The Klipschorn (AK6) has a fully enclosed low frequency horn and no longer has to be flush to the corner in order to operate properly. The Klipschorn can now be toed in or toed out to obtain the best imaging. The corner still serves as an extension of the low frequency horn, improving low frequency performance. For best results, Klipsch highly recommends the Klipschorn be placed in the proximity of a corner."

A note about my listening room: It occupies the major part of a single-story addition to my 1936 brick house. Two of the room's four walls are exterior walls, and a thirdthe wall that adjoins what was once the house's brick back wallis effectively an exterior wall, making this an extremely sturdy, stiff-walled room. The room measures 17' long by 12' wide, with an 8' ceiling.

Listening

I began with the backs of the Klipschorn AK6s a short distance from the front walltheir front surfaces, measured at the centers of the cabinets, were a little more than 3' from that wall, and a little more than 8' apart from each otherand with the speakers slightly toed-in toward the center listening seat. At first, I relied on my reference Shindo Haut-Brion power amp, which uses push-pull 6L6 tubes, operated as pentodes and without feedback, to deliver 20Wpc.

Footnote 1: Actually the early 1960s.