KEF KF92

KEF applies Newton's Third Law to its dual-driver bassmaker, so Steve Withers searches for his lab coat and Godzilla disc

- Steve Withers

IF YOU MANAGED to stay awake during physics classes at school, you might remember Newton's Third Law of Motion, which states - in essence - that every action has an equal and opposite reaction. It's a principle of classical mechanics that's been embraced by speaker and subwoofer manufacturers, allowing them to engineer a force-cancelling design to reduce cabinet vibrations and increase the maximum output.

KEF is no stranger to it, and claims to have launched the first commercial speaker with a force-cancelling driver configuration, in the shape of the Reference 104/2 floorstander in 1984. More recently the company has been using this approach in its subwoofers, with the flagship Reference 8b, mid-range KF92 (tested here), and dinky KC62 (see HCC #320) all benefiting from a force-cancelling array.

The KC62 differs slightly by using a single, overlapping Uni-Core voice coil for its two 6.5in woofers (allowing it to be extraordinarily compact), but all three employ the same design idea of two drivers positioned back to back. The KF92's are 9in units with a hybrid aluminium/paper cone, plus 'oversized' motor system and voice coil.