Subwoofers

All speakers operate on the same basic principle of generating sound by physically moving air. The bigger the driver, the more air being shifted and the lower the frequencies. At the end of the day there's no replacement for displacement, so if you want big bass you need a big woofer.

M&K Sound's X+ Series of subwoofers perfectly encapsulate this philosophy. The new lineup, which builds on the platform of the earlier X Series, features three new THX-certified subwoofers – the X10+, the X12+ and the X15+. While the first two are upgraded versions of existing models, the flagship X15+ is a completely new design and the company's first woofer to be certified THX Dominus.

All three use a push-pull driver configuration, aiming to reduce distortion and increase bass potential output. With the X15+ sporting a pair of 15in woofers, there's no prize for guessing the size of those found in the X12+ and X10+.

M&K Sound's drivers are a new 'ground-up' design, engineered, we're told, to match the X+ Series' (also new) amplifiers. Cones are hewn from carbon fibre for improved strength and rigidity, allowing them to handle increased power and excursion; CNC-machined, extruded aluminium 'Distortion Killer Shorting Rings' are deployed within the driver motor assembly for further control; surrounds have been uprated from polymer-coated foam to nitrile rubber; and the aluminium voice coil is a monster 75mm diameter design. There's a lot going on behind the scenes (or in full view actually...).

Driving the X+ Series woofers are ICEpower Class D amps. Opting for high-efficiency Class D, rather than Class AB, makes complete sense when the desired power output is 700W (RMS – with peaks up to 1,400W), as it is here.

Smoothly Does It
M&K's cabinet features a new 25mm MDF construction with further attention paid to bracing to minimise vibrations and control resonances, and the cosmetics have also been given a makeover and now mirror M&K's matte black S150 and S300 speakers (HCC #289). The recessed front baffle has been replaced by a smooth facade, with magnetic grille attachments rather than the pegs used previously. Finally, the threaded inserts on the subwoofer feet provide the option of acquiring after- market spikes or vibration isolators.

The first thing you notice about the X15+ is that it's about the size of a fridge/freezer (despite M&K insisting its push-pull driver implementation allows for a ' smaller cabinet volume'). This is a serious subwoofer that stands nearly a metre high and weighs over 60kg. The THX Dominus certification (a new category) shows it's intended for home theatres up to 184 cubic metres, with a six-metre viewing distance, but it's surely likely to find its way into smaller rooms owned by serious bass addicts – once they've found a mate to help them lift it.

The second thing you'll notice is that driver mounted at the bottom, firing upwards and into the cabinet. This is effectively two subwoofers in one enclosure, with this inverted driver out of phase with the front-facing unit. It looks weird, but works wonders.

The most difficult aspect of setup was actually getting the X15+ into position, but after calling in a few favours it was installed in an area of my home cinema I know has an even bass response. I connected it to my Trinnov Altitude16 AV processor using balanced XLR cable, although there are also RCA inputs if your prefer.