KC62 feedback

Not kif herb but KEF Herb. Whilst waiting on my own KC62 loaner to breach the company's back-order embargo, I read Herb Reichert's Stereophile review for more anecdotal facts. Each reviewer uses different hardware, different rooms. More data equals more utility for a reader or potential shopper. Herb's first speaker mates were Falcon LS3/5a, a re-issue of the famous BBC 4.5" 2-way location monitor. He measured his for an in-room 80Hz reach below which they fell off sharply. With the KEF's low-pass at 60Hz, he enjoyed "the flattest 40Hz–200Hz response I have ever achieved in my room, with any speaker. Below 40Hz, response [with the sub – Ed.] dropped off by 6dB/oct." That used the sub's 'room' EQ. "With the KC62 dialed in, midrange presence and spaciousness were improved in ways that made it easier for me to look into the soundspace and stay focused on performances. Instruments and voices sounded bigger, more physical and easier to 'see' with the KC62 engaged."

His second speaker mates were the companion 6.5" 2-way LS50. In his room they measured -9dB/40Hz solo, just -1dB/40Hz with the KC62. "Rhythmic flow was more liquid than usual and the soundstage had expanded in every direction… the LS50 was more clean-glass transparent through the midrange and high frequencies." When he filtered the LS50 through the sub's high pass, his favored filter hinge was 40Hz. The measured response now was -5dB/31Hz, up over the -22dB solo figure. "Midrange clarity improved even more. But what impressed me most was how now, with the LS50s running through the high-pass filter, subtle changes in rhythm and tempo became more obvious…With the KC62 sub, the LS50s sounded more relaxed, tonally even and natural."

Herb's third speaker mates were Magnepan 0.7 which in his room start their roll-off at 80Hz. High-passed, his best response came from a 60Hz transition which now gave a -10dB/30Hz reach. But, "I did not like how the KC62's circuitry was diminishing the ease and natural transparency of the .7's midrange and ribbon highs. That setup measured almost perfectly but the sound felt staid, artificial and homogenized." Herb preferred adding the KC62 with just its low-pass filter.

Breaking these findings down, we have 3 x speakers, 2 x successful subwoofer add-ons and 1 x success where filtering the mains was superior. For the low-pass additions, we read of more and lower bass but also benefits to midrange presence and general soundstaging including improved transparency up into the high frequencies. The high-pass integration brought further clarity into the midrange plus improved subjective timing. The second high-pass attempt caused the overall sound to go "staid, artificial and homogenized".

Without being given more, as a reader I'm left wondering. How can the same high-pass filter produce such different results? Why wasn't it tried on the Falcons? How can a sub in add-on mode improve anything past its own bandwidth? As a reviewer with prior sub experience, I do have an answer to the second question. Adding bass can affect our sense of the remaining bandwidth. Even though nothing there alters per se, we can hear better contrast and more spatial cues. Those qualities then register as more clarity and separation. I'm not sure whether we can invoke 'psychoacoustics' but our perception certainly can respond in these ways particularly when the speakers being subbed are as bass shy as are Herb's BBC minis and Magnepans. Like adding a well-integrated super tweeter can seem to affect the bass, more bass spreads its effects on our perception far higher up than they do on paper.

As a listener who owns external active analog hi/lo-pass filters to bypass a sub's own, I'm familiar with the potential for minor opacity/flatness when one runs a premium analog signal through an affordable sub's A/D, DSP and D/A path for a filtered signal which then feeds the speakers' amp/s. That's what Herb described with his panels. Though measuring perfectly in the frequency domain, he didn't like the sonic homogenization so returned to just tacking the KC62 onto the unfiltered panels. But why did the same signal degradation not happen to his LS50 which sounded even better in filter than add-on mode? Are the quasi-ribbon panels of so much higher resolution as to be that much more critical of KEF's preceding DSP shenanigans?

As a fellow reviewer, I was surprised to see no mention of DSP latency—the KC62's happens to be just 0.5ms which works out to a very small delay equivalent to ~17cm of extra distance—and the related subject of time alignment. That very obviously rears its head when we move a subwoofer into a corner for maximum boundary gain. It now sits farther from the seat than our main speakers. That incurs a time delay (3ms/meter) even with zero DSP latency. Late bass is slow bass. That's a critical consideration. I was disappointed to see no basic explanation of the benefits from actively high-passing 2-way main speakers. By removing low bass from their signal path, the main amp is destressed as are the excursions and voice coils of the monitor's mid/woofers. Lower voice-coil temperatures mean lower Ω so better dynamic response across that driver's bandwidth. In a 2-way, that goes all the way up to the tweeter. Smaller excursions without low bass also mean lower distortion. Those aren't just 'psychoacoustic' effects but very real electrical/acoustic benefits. When the active high-pass filter becomes an external pure analog affair to not cause resolution and S/N losses, the benefits to dynamic expression, spaciousness and detail magnification over the speakers far exceed what's possible with an add-on subwoofer. Just tacking on a sub can't do any actual strain relief for small speakers or their amp. Finally MIA was any mention on directionality as the difference between turning a force-cancelling subwoofer so that its woofers aim sideways versus rotating it 90° so one woofer faces the listening seat directly. There is a difference. In any case, with 2.1 systems being so rarely discussed in the hifi not home-theater space, all the coverage which the topic can scare up is definitely merrier. So a round of applause for Herb!

Now a drum roll for John. In his KC62 video review published May 27th, John discusses the main benefits of adding the micro sub to his KEF LS50 Meta and Wireless monitors. The former were used in wired augmentation mode, the latter also in wireless high-pass mode. Then the frequency-band assignments occurred inside the monitors as prompted by their app. Being John's first-ever subwoofer review, it took him a week to find the very best position for it. That ended up being front-row center so right between the monitors. His first takeway after having locked in proper low-pass and sub volume settings was greater listening satisfaction at lower SPL. I hear exactly the same with our Dynaudio sub and find this advantage far more important than it is usually given credit for if at all. John also found that the addition of sub 40Hz bass to the monitors made the overall sound bigger, fuller and a bit warmer. Despite expectations to the contrary kindled by findings published elsewhere however, he heard zero improvements "above the waist" as he phrased it. Augmentation mode didn't do anything for extra midrange clarity, staging acurracy or subjective treble sweetness. Because high-pass mode would have required additional long interconnects and a pre/power combo to replace the Hegel integrated, for this introductory report he didn't try it on the Meta.

He did however with the Wireless. That used the KC62's optional wireless kit with its 17ms latency which KEF compensate by delaying the mains by the same amount. Besides the same benefits of more bass, now he also heard extra midrange pop, dynamic expression, openness and stage height. He also found that the sound no longer tried as hard to seem more easeful. To get these goodies simply relied on filtering the monitors so they no longer saw any low bass at all. Between his two 2.1 options, why did he still prefer the Meta in augmentation mode? Because the €5'000 Hegel 390 integrated which powers them renders their treble more agreeable than the amp which KEF built into the LS50 Wireless depicts their top end. To his ears, the comparative losses the Wireless exhibits in its top end weighed more than its midrange gains from high-pass mode. He finally experimented with the KC62's orientation and found it to integrate the very best when it matched the mid/woofers of the monitors. That meant firing one of the sub's woofers directly at the seat and the other at the front wall rather than aim both sideways. John is working on a written follow-up to cover details that couldn't make it into his 30-minute video. That's still more anecdotal data for our communal hifi library on the 2.1 system approach. Bravo!