ProAc • Response K6 Loudspeakers

by Marc Mickelson | December 23, 2011


In the mid-1990s, immediately after buying my first house, I did something a little crazy -- at least by the standards of some of my friends and family. I bought a pair of speakers that cost one-fourth as much as the house -- ProAc Response Fours. What set me on this course was a weekend-long audition of ProAc's Response 3.5, a tall, svelte two-way floorstander that used a pair of 6 1/2" polypropylene woofers and what was the most wondrous driver I had heard up to that time: ProAc's modified silk-dome tweeter, which was sourced from Scan-Speak. What was so significant about this tweeter was its unerring sense of reality. With it, the Response 3.5 was utterly devoid of the high-frequency glare and hardness that plagued essentially every other speaker I had heard up to that point -- and was not an artifact of live music. The 3.5s were so extraordinary, so human, that I couldn't forget them -- or settle for less. So I settled for more -- the five-foot-tall, 300-pound Response Fours.

Since then, I have continued to follow ProAc closely. At CES, US distributor Richard Gerberg of Modern Audio has dutifully demoed a new model every year -- sometimes to vex me, I'm convinced. In 2010, it was the Carbon Pro 6, the penultimate speaker in ProAc's line, and early this year it was the Response K6, a speaker commemorating ProAc's 30 years in business. The K6 seems like an odd duck for ProAc until you learn a bit about it. The form is recognizable, as is the size, which is similar to that of the middle Response-series speakers like the 3.5, 3.8 and D38. Those are all two-ways, however, while the K6 is a three-way, adding a dome midrange to the dual-woofer-and-tweeter complement.

However, the drivers are radically different from those used in earlier ProAc speakers. Pro-driver maker Volt manufactures the dual 6 1/2" woofers, which are dissimilar to any others the company makes due to their Kevlar cones. ProAc has these made to its specifications by a supplier local to its Brackley, Northamptonshire, UK environs. Each cone is formed under pressure, then cured in an autoclave -- a kind of industrial pressure cooker -- for four hours. After it cools, it's removed from the tooling and inspected. Volt trims every cone to size, after which it is concentrically weighted to bring it to the correct specification, and only then does it become part of a K6 woofer. At CES, Graeme Bridge of ProAc gave me one of the rejects, which is as thin as a sheet of paper but weighs half as much. It's exactly as billed: very light and very stiff. What more could you want for a speaker cone?

The K6's dome midrange comes from Visaton in Germany, which modifies it at their factory to work with the mounting plate that ProAc adds to provide a modicum of horn loading. This piece is machined from T6061 aluminum. The K6's ribbon tweeter would be considered radical for the company had ProAc not used a ribbon driver all the way back in its short-lived Future series. The K6's tweeter, which is of Italian design and Far East manufacture, also has a custom-machined T6061 mounting plate.

The cabinet is bottom ported, a feature ProAc launched with its earlier D28 and D38 models. The cabinet proper is mounted above the plinth to give an outlet for the port's output. A pillar in front provides support for the large gap between cabinet and plinth. For the K6, the port is larger than normal -- "a monster 4" diameter," according to Bridge. "Typically you find large-diameter ports on pro and PA-type speakers, which is Volt's core business," he explained. The cabinet is fashioned from MDF of varying thicknesses and coated internally with sheets of bitumen, which line the inner chambers. This changes the resonance properties of the MDF and provides damping for the drivers' backwaves, both of which are vital design considerations. The cabinet's proportions and veneer, not to mention the silver accents, strike my eye as being collectively attractive. The K6es look best without their grilles, and this is ProAc's recommended way of listening as well.

Unlike the big Tidal Sunray speakers, which left my room just as the ProAc speakers arrived, the K6es were not at all difficult to set up, place or optimize. They are packed fully assembled, and they weigh around 100 pounds each, so they're easy to unpack and move. More important, they sounded good everywhere I placed them, which made optimization tricky -- an act of picking the best between superb and excellent. I suspect that their bottom porting contributed to their in-room agreeability, as there was no port output to account for near walls. Toe-in wasn't particularly critical, as ribbon tweeters are prized for their horizontal dispersion, although, as the way of fine-tuning the ratio of treble sparkle to midrange presence, it wasn't arbitrary either. Ear height and rake angle can skew the speakers' spectral balance, a product of a ribbon tweeter's limited vertical dispersion. Just make sure your ears when you're seated are within a 3" window above or below the tweeter's center and you'll be fine.

I shifted and played the speakers for weeks, never actually settling on single spots for them, because they never sounded wrong in any position. Again, the tweeter has very good lateral dispersion, but there was definitely a best-of-all-possibilities toe-in point in my room. This, with the speakers roughly ten feet apart center to center, had the drivers' output crossing a foot behind my head as I sat nearly ten feet away. I can envision K6 owners spending weeks moving their speakers around in an attempt to pull ever more from them. This wasn't a futile exercise in my room, but it was one that cut into my listening time. If you own a pair K6es, knock yourself out.

The advantage of a ribbon tweeter comes from the lightness of its membrane, which makes for fast acceleration, extended frequency response, and resonance above the threshold of audibility. If ribbon tweeters have any collective sonic tendency, it's toward excessive energy in the cymbal region, which can become overlaid with splashiness and superfluous reverberation. The sonic tendency of ProAc's ribbon tweeter was quite different. There was an unerring naturalness, which is the exact opposite of the performance of lesser drivers -- or lesser implementations. In the hands of Stewart Tyler, the head of ProAc and the person responsible for the voicing of each speaker, it could be no other way, as he does his best work in the upper frequencies, teasing all of the speed and air from the ribbon but not accepting excesses.

However, even after a very positive demo at CES, I was skeptical, thinking that the ribbon would represent a tradeoff from the silk-dome tweeter I had come to know and admire -- and more likely a step backwards. This wasn't the case. Once I had the K6es set up in my room, their treble retained the sweetness and presence of earlier ProAc tweeters but added quickness into and out of each note along with bite, especially with brass, which never sounded better, even with pricey diamond-dome tweeters. My test for this is Parker's Mood [Verve 314 527 907-2] by the Roy Hargrove / Christian McBride / Stephen Scott Trio, a disc that (you guessed it) is homage to Charlie Parker, the father of bebop. The numbers are mostly Parker compositions, each performed in trio, duo or solo arrangements. This CD has some of the most realistic-sounding horns I've ever heard from a recording, especially on the title number, and when they cut loose, it's not always pretty, stressing a tweeter with their quick burst and metallic "blat." While the ProAc ribbon had no problem with either of these, it also retained the composure of the earlier silk-dome models, never turning harsh or ugly, even as the music pushed it in this direction.

This driver proved to be all gain and no pain -- just as early ProAc tweeters had been, but with improved uppermost extension, which was responsible for the sense of air that recordings achieved. The K6es were by no means clinical- or analytical-sounding speakers, and yet they were still highly detailed in the treble, which seemed to embody everything great about ProAc's silk-dome tweeter and the best ribbons.

In Stewart Tyler's hands, this tweeter is special, but more surprising -- and immediately so -- were the K6es' two midsize woofers. "Amazing bass," say my listening notes, followed by "tight, powerful, textured and quick." The K6es rumbled and roared down low in a fashion that belied their size -- and especially the size of their woofers. The bass was more taut than bloomy, however, even with the generously portrayed upright bass on Parker's Mood, but it didn't lack for extension and sock when it was present in the music. Both are in abundance on Walter Becker's 11 Tracks of Whack [Giant 24579-2], and the K6es conveyed all of the throbbing power without chuffing or overhang, while also doing justice to the purr of Suzanne Vega's Nine Objects of Desire [A&M 540583]. Both of these CDs are equally taxing, but for different reasons, and the ProAc K6es handled their demands with an inherent effortlessness that required no excuses to be made, including for their dynamics. You can drive the K6es with lower-powered tube amps like the Lamm ML2.2s, given the speakers' quoted 90dB sensitivity. Tonally and in terms of in-room presence, this combination was supreme, even if bigger power, specifically from the Lamm M1.2 Reference and Atma-Sphere MA-2 Mk 3.1 monoblocks, produced better transient pop and definition along with more freewheeling dynamics.

The K6es' midrange pulled everything together, deftly transitioning from the sheer resolution of the treble into the quickness of the bass with purity and directness. The mids were neither rounded nor full, and they displayed no tonal excesses that could translate to fullness or warmth. They captured the essence of vocalists as diverse as Billie Holiday, Greg Brown and Norah Jones, displaying ample throatiness along with the presence that originates in a singer's chest. It's one thing for speakers -- or any piece of audio equipment -- to parse qualities of the sound and another to integrate those qualities throughout their range and thus with the artistic intent of the performers. The K6es achieved the latter, making for a coherent and continuous musical presentation, one whose midrange was not neutral simply for the sake of being so. It was as though the speakers somehow understood what the artists were trying to achieve and helped them in their musical endeavor.

These midsize speakers played big, casting a soundstage that was as wide as I could position them without obscuring the center image, as deep as the upstream equipment and recording allowed, and -- surprising again -- as high as speakers that were half again as tall. Speaker height isn't an indicator of the ability to convey height information in recordings. Some tall speakers don't do it as well as some smaller speakers, like the K6es, which were able to give the illusion of singers standing in between them. Given the limited vertical dispersion of the ribbon tweeter, this seemed peculiar, and yet there it was. And it converged realistically with the lateral spread and depth the speakers achieved, never causing a piano to sound bigger than it should. The Music Matters Blue Note LPs I played filled the business end of my rather large listening room with images that, if they weren't truly life-sized, were much more substantial than expected.

Yet, this, along with the treble and bass, were just the icing. The cake with the K6es was their tonal sophistication, the way in which they conveyed the "ness" of instruments -- their unique character. The K6es were those rare speakers that walked the line between truth and beauty with a steady gait, achieving both without leaning one way or the other. Earlier ProAc speakers were either slightly or overtly on the side of beauty, and that's frankly one of the things that drew me to them, as their presentation aligned well with my own ideas about live sound. But the K6es delivered truth in abundance -- balancing presence with spaciousness and solidity with air. Their tonality was undeniably refined and their bandwidth undeniably wide. They could be subtle or overpower to a level that more than once caused disbelief in their ability to do so. These were truly compelling speakers that seemed to do everything important to reproducing music, conveying both realism and involvement.

The Wilson Audio Sophia 3s ($17,900/pair), which I've also had in my room recently, made for an interesting compare-and-contrast exercise with the ProAc K6es. The Sophia 3s are also three-ways, but they sport a single 10" woofer in their stout, very heavy cabinet. The Sophia 3s are Wilson speakers through and through, having massive output capabilities and wide bandwidth, an expressive midrange, and an overall nonanalytical mien. Much of this applies to the ProAcs as well, but the greatest differences are high and low. The K6 tweeter has slightly quicker launch and conveys more of the overtone-rich aura of horns than the Sophia 3's tweeter, and its bass, while not displaying as much heft and ambient spread, is quicker off the mark and slightly more expressive of dynamic shifts. With the Suzanne Vega CD, for instance, the Sophia 3s emphasized solidity and presence throughout their range, the K6es transient speed, recording-venue atmosphere and instrumental texture, while sounding generally -- in terms of sweetness, midrange detail, and overall ease -- more alike than different. I preferred the additional speed of the ProAcs, along with their great expressiveness, at least as I listened to the speakers many weeks apart.

I discussed in my last speaker review, of the big Tidal Sunrays, the speaker-sequencing square-dance I was performing after The Audio Beat launched in 2009. I went nearly two years without my reference speakers playing a single note, as I dutifully dragged others into and out of my listening room. These speakers represented a cross-section of design theories and outcomes, as well as prices. They started at $8000 per pair and topped out at over $150,000, and the driver and cabinet technologies they represented were as different as the ways in which they portrayed the music.

Amidst this diverse and accomplished group, the ProAc K6es were in many ways the best of them all, offering performance that was bettered in specific ways by one or another of these speakers but always in the running in an overall sense, even with speakers that were multiples of their price. In fact, one that cost much more than the K6es was not as satisfying to my ears, which is a testament to Stewart Tyler's ears. While it would be easiest to write this off to my longtime acclimation to the ProAc sound, this wouldn't take into account the evolution of the company's speaker line, as the continuing development of new drivers and design methods has brought to bear.

When I bought my long-departed Response Fours all those years ago, I couldn't fathom that a speaker like the K6 would come from ProAc -- smaller, slightly less expensive, more technologically advanced, and better sonically in every way. It is a lesson in progress, one that I'm very glad to have experienced for myself.

Price: $24,000 per pair in standard finishes. Optional veneers are available at extra cost.
Warranty: Five years parts and labor.

Highpoint House
Riding Road
Buckingham Road Industrial Estate
Brackley, Northamptonshire, NN13 7BE
United Kingdom
+44 (0) 01280 700147

Associated Equipment

Analog: TW-Acustic Raven AC turntable, Graham B-44 Phantom Series II and Tri-Planar Mk VII UII tonearms, Dynavector XV-1s (stereo and mono) and Allnic Puritas cartridges, AudioQuest LeoPard and Nordost Odin phono cables, Allnic Audio H-3000V and Audio Research Reference Phono 2 phono stages.

Digital: Audio Research Reference CD8 CD player, Ayre Acoustics DX-5 "A/V Engine."

Preamplifiers: Allnic Audio L-3000, Audio Research Reference 5 and Reference Anniversary.

Power amplifiers: Atma-Sphere MA-2 Mk 3.1 monoblocks, Lamm Industries M1.2 Reference and ML2.2 monoblocks.

Loudspeakers: Wilson Audio MAXX 3 and Sophia 3.

Interconnects: AudioQuest William E. Low Signature, Shunyata Research PowerSnake Series Anaconda and Python.

Speaker cables: AudioQuest William E. Low Signature, Shunyata Research PowerSnake Series Anaconda and Python.

Power conditioners: Essential Sound Products The Essence Reference, Shunyata Research Hydra Triton.

Power cords: Essential Sound Products The Essence Reference and MusicCord-Pro ES, Shunyata Research CX-series (various).

Equipment rack and platforms: Silent Running Audio Craz² 8 equipment rack and Ohio Class XL Plus2 platforms (under Lamm M1.2 amps), Harmonic Resolution Systems M3 isolation bases.