Subwoofer Reviews

KC92s with the PS Audio Aspen FR5
This user configuration is one of the most likely for the KC92, and I found that it worked well. Setup with these small standmount speakers was not as streamlined as with LS60s since the KEF app does not know them. One could use an external program (eg, Roon, JRiver, etc.) to split off the bass to the KC92s and high-pass the rest to the FR5s. Instead, I connected the full-range L/R signals to the subs and fed the main amps and FR5s from the KC92s' line outputs (footnote 4).

Physically, I placed the FR5s where the LS60s (which are usually my surround speakers) had sounded best. I kept the same RoomEQ setting (Corner) and used REW and my ears to tweak the balance with the sub's volume, LPF, and HPF controls. I got the smoothest response with an 80Hz crossover that gave the FR5s an increment of appreciated gravitas. With Buster Williams's solo acoustic bass fiddle of "Concierto," derived from Rodrigo's Concierto de Aranjuez (from Griot Liberté; rip from SACD, High Note HCD 7123), one could hear and feel each note, many of which have their fundamental at 100Hz or lower, with the weight and impact the FR5s could not provide unassisted. That's but a single example, and I'll defer the rest for the full review of the FR5, which was published in Stereophile's December 2024 issue.

KC92s with the KEF Blade Two Meta
The KC92s did a great job in extending and expanding the sound with the compact speakers, but I was not certain they could be as effective with these large speakers, despite assurances from KEF that they would. The system configuration is three Blades (L/C/R) up front with the KC92s on the floor in the front corners and the LS60 pair on the side (LS/RS) (footnote 5). Dirac Live with Active Room Treatment (DL-ART) was used for both bass management and room EQ. Measurements showed that the Blades were effective down to the 20–25Hz range, the right LS60 to about 28Hz and the left LS60, at the end of a wall and adjacent to a room opening, to 35Hz. Each of the KC92s—see figs.1 & 2—extended to 15Hz before rolling off! DL's default crossover of 70Hz was a good start but, since DL-ART uses every bass source to support all the others up to 150Hz, the nominal crossover is not relevant.

After creating several correction filters by varying the target curve, including a flat response, I ended up preferring a Harman-like curve with a boost of 5dB at 20Hz, transitioning to 0dB from 200Hz to 1.5kHz and then rolling off to –2.5dB at 20kHz. The result (compared to playback with a similar Dirac target curve but without subs) was remarkable, particularly, from the lower midrange down, the range that encompasses the lower range of most instruments (middle C on the piano is about 262Hz) as well as adult voice fundamentals. On the one hand, there was a general increase in presence, weight, and dynamic impact, while on the other, every voice or instrument seemed more clearly defined, as were the ambient hall sounds when they are captured. It is not just a matter of deeper bass—the KC92s do extend below 20Hz—but, with the aid of DL-ART, they help remove the smudgy fingerprints of room acoustics.

The effects were dramatic with two fairly different stereo tracks: "Stimela (The Coal Train)" (from Hugh Masekela's Hope; rip from SACD, Analogue Productions APJ 82020); and "The Glass Hall (Choose the Crystal)/The Play of the Five Balls" (from Andreas Vollenweider's White Winds; 16/44.1 rip from CD, Columbia MK-39963). Both recordings have great impact and, paradoxically, an open and huge soundstage. The first captures a spacious, truly live event and the second is a totally synthetic studio creation. Via the Blades/LS60s/KC92s (and DL-ART), both were dynamic and credible, their soundstages disassociated with the speakers, and approached the immersion of true multichannel. Moreover, because of the suppression of room acoustics, I could play them as loud as I wanted without the sound blocking up and overwhelming the room.

A recent well-produced multichannel recording of Prokofiev's (yes, him again) Symphony-Concerto for cello and orchestra, Op.125, with cellist Christian Poltéra (Anja Bihlmaier conducting the Lahti Symphony Orchestra; SACD, 24/96, 5.0 download, BIS BIS-2617) provides a more subtly spectacular demonstration. From the very opening, the orchestra was arrayed before the listener with enough specificity to conjure it visually. Most notable was the texture of the bass fiddles and cellos on the right and the upper strings spread to the left. When Poltéra entered at left front, his cello had the presence and warmth more commonly achieved in chamber performances and, despite the intimate detail, all this is in a concert hall; I have been transported there since my own room's acoustics no longer intruded.

As for whether these small subs are the equal of the large subs that HT buffs dote on: A friend of mine just installed a pair of 371lb, 4000W, 21" behemoths, so no. The KEFs could keep up with any level that I could tolerate playing music in my room, but if that's not enough for you, the KSK92 Subwoofer Stacking Kit lets you stack and daisy-chain KC92s, ad lib.

Keepers!
The KEF KC92 subs did exactly what I had hoped they would in better matching my Blades to my room and reinforcing their bass substructure, but clearly, they can do more. I hooked them up with ease to the KEF LS60 Wireless speakers, which elevated these highly capable, compact loudspeakers into the big speaker leagues. They did much the same for the even smaller PS Audio FR5s. The only remaining matter is their cost compared to similar-sized dual-driver subs. I think the KC92's construction, design, and feature set easily distinguish them from less expensive subwoofers, and I question whether pricier ones can offer higher performance given their size limitations. The KEF KC92 is a sweet spot for subs.

Footnote 5: My rear sub, an SVS SB-2000, was disconnected, temporarily, for this review.