Loudspeakers

Although KEF’s KC62 subwoofer [pictured below] appears to be a close relative of the ’92, its compact dimensions necessitated a different engineering approach to the force-cancelling driver array. The KC62’s two 6.5in/165mm opposed woofers, again hybrid paper/aluminium cones with ‘P-Flex’ surrounds, are not mounted ‘back-to-back’, due to space limitations inside a cabinet measuring ~250mm in all directions. Instead, KEF’s engineers developed ‘Uni-Core’ technology, which combines the drivers’ two voice-coils in a single motor system. To achieve this, different diameters are used – the smaller coil is placed concentrically within the other, allowing the coils ‘to travel within their own gap without colliding’ along the central steel polepiece.

This means a single magnetic flux path, so one of the Uni-Core voice coils is wired in inverse polarity. Additionally, the variance in the coils means the KC62’s two drivers themselves are not identical – KEF used FEA modelling to optimise their suspensions, and added a ‘small mass’ to the driver with the smaller coil to compensate for the higher mass of the opposing coil/driver. Attention was also paid to the subwoofer’s cabinet, with extruded aluminium being preferred to conventional MDF/HDF to enable thinner walls (thus more internal volume), improved rigidity without internal bracing, and better heat dissipation.