Subwoofers

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 this particular physical law, 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.

Now, the KC62 differs slightly from the other two models 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.

These back-to-back drivers aim to cancel out the relative forces that stress conventional subwoofers designs, keeping the delivery balanced while allowing the KF92 to reach a claimed response that goes down to an abyssal 11Hz (-3dB). A pair of 500W (RMS) Class D amplifiers produce the necessary power.

Although not as bijou as the KC62, the KF92 is a surprisingly compact sealed cube with a superb level of construction and a gorgeous glossy black finish. At 20kg it won't murder your back either, which makes a nice change from many models around this price point. The sub sits on solid rubber feet for improved isolation, and there's a low- profile heatsink at the rear to keep all the internal electronics at optimal temperature.

These electronics are built around what KEF refers to as its Music Integrity Engine, a DSP implementation that – a version of which – you'll also find in the brand's active LSX speakers. This includes 'Intelligent Bass Extension' filtering to optimise performance, and five self-explanatory placement-dependent EQ options, selected by a switch on the rear panel. The 'apartment' setting is presumably for those who don't want to receive a restraining order from their neighbours.

Whatever your needs this sub is very easy to install and set up. Also on the rear are controls and terminals for crossover, volume, phase, LFE and stereo line in/out. A space-saving Phoenix connector is used for the speaker-level inputs, but most folks will be using the LFE output from their AV receiver. In which case, just plug in the cable, switch the mode to LFE, and choose the most appropriate EQ setting.

Punch Drunk Love
KEF claims the KF92 delivers 'astonishing levels of deep and controlled bass', so let's put that to the test with the reigning champ of seismic low-end extension. Godzilla vs Kong (4K BD) is a movie that uses so much bass it's the perfect marker for establishing how much sustained energy this sealed sub can actually deliver.