Brain juice

Unicorn sighting? Only if you misspell it. KEF's Uni-Core array is very real. It's a patented solution to move two force-cancelling woofers into 1/3rd closer proximity by sharing one motor system with concentrically sleeved voice coils. The first model to exploit this invention is today's KC62, a black or white micro subwoofer which combines two 6.5" force-canceling woofers with 1kW of class D power inside an extruded 14kg aluminium chassis of ultra-compact 246 x 256 x 248mm proportions. There are five DSP presets: room, wall, corner, cabinet and apartment. With them we input automatic boundary gain compensation. The same DSP also includes a smart limiter to avoid overdrive should our inner headbanger emerge.

Next come 105dB max SPL and a shocking -3dB/11Hz reach claim. Compare that to the recently reviewed ModalAkustik MusikBass. That began its 6dB/oct. acoustic roll-off at 35Hz to be -6dB at 18Hz despite 2 x 12" woofers. That's because its so-called RiPol loading, whilst categorically avoiding room pressurization effects by operating as a velocity converter instead, also caused serious out-of-phase cancelling from dipole radiation. With KEF's standard 180°-radiating pressure generator type, the RCA-based 4th-order 24dB/oct. low-pass filter is 40-140Hz variable. LFE signal already filtered in an AV receiver or pre/pro bypasses it. A matching high pass on RCA outputs can alternately daisy-chain another subwoofer. Speaker level inputs via push connector are provided as well. The KC62 is the Brit's first model to exploit their new Uni-Core array. Its drive units use another company exclusive called P-Flex aka origami surround. Scroll back for the lead image to see its internal geometry. As Fostex and Purifi do with their own suspensions, it exploits pleats to better resist the acoustic pressure in the cabinet without decreasing sensitivity like traditional half-roll surrounds. Finally there's a 3rd KEF innovation by way of patent-pending real-time motion feedback accomplished without a sensor. That reduces distortion for tighter signal tracking by monitoring the voice-coil current. Philips had early sensor-based motion feedback decades back and various so-called servo subwoofers including Velodyne's applied their own take. KEF call theirs Smart Distortion Control Technology.

These three innovations follow KEF's earlier meta material as a type Medieval labyrinth-shaped diffuser which absorbs 90% of rear radiation when mounted behind a tweeter. Someone at the company's R&D lab must be drinking hyper-caffeinated brain juice. Innovation stimulates evolution. Those who insist that nothing new happens in hifi should keep an eye out for KEF. Their team clearly aren't content to rest on their laurels and of late have bowed a number of inventions which promise to advance the state of our audio arts.

Seamless seamstress? Here we see the control panel's functions.

The graphic below shows how to hook up two subwoofers from either a pre/pro's LFE output or a preamp or integrated's pre-out. At left we see the dip-switch options for the high pass. That determines at which frequency the main speakers blend out. Trying to produce bass that's beyond them still taxes their mid/woofer or woofer by raising its voice coil's temperature. In an inverse square function, rising heat drives up impedance/resistance which chokes dynamic range higher up.

Relieving a main speaker of the lowest bass thus can benefit its sound quality. That's particularly true for smaller bandwidth-limited monitors. The obvious prerequisite for unblemished success is a top-quality preceding high-pass filter.

KEF's next-size-up subwoofer model is the KF92. That scales up to dual 9" woofers and a cabinet that's 63% bigger. Yet the only thing that going bigger buys us are 5dB more max SPL. 1000Wrms amplification and -3dB @ 11Hz carry over from the mini. Recommended room sizes are 5-50m² for it, twice that for the bigger unit.

The built-in DSP engine exploits the surfeit of available power and long-stroke origami suspension to optimize intelligent bass extension which counters expectations re: size, loudness and reach. That's coupled to a rev limiter to protect the device. 'Apartment mode' is mindful of LF bleed through walls which could annoy the neighbors. When selected, it attenuates the very low frequencies.

The basic force-cancelling topology minimizes the severity of physical vibrations driven into the enclosure whose sealed aluminium build anticipates very serious internal pressurization. In the olden days, Bob Carver's diminutive Sunfire subwoofers were notorious for going walkabout. We sold them at the Bay Area store I worked in at the time. I distinctly remember their silly propensity for not staying put because of the asymmetrical forces at work. They also suffered high distortion as value-subtracted tax for counter-intuitive power from a small enclosure.

Fast forward the DSP clock to 2020. Locate it inside an engineering-driven company like KEF. Call out the talking points. Digital signal processing. Motion feedback. Overdrive limiter. Custom drivers with specialty suspensions. The sum of these ingredients promises significant progress from Sunfire to now.

Naturally current and future owners of KEF's popular LS50 variants will be prime candidates for the size, curvy cosmetics and price of the KC62. Hello optional €199 KW1 wireless subwoofer adapter kit.

It consists of a transmitter and receiver for wireless 5GHz transmission without compression and low 17ms latency for home-cinema lip sync and proper music timing. Such bass data transmit at 24-bit/48kHz. Wireless reach specifies as 15-30 meters. The transmitter powers directly via USB,  the receiver from the KC62's expansion port.

If you have ground-loop gremlins careful routing and proper power delivery can't exorcize, there's even a ground-lift switch.

Based on the evidence of raw specs and photos, the li'l very handsome KEF KC62 cube promises performance we've never yet heard from a sub this compact. Lock-down and bitter Brexit as the mothers of invention? If so, hello baby!