Loudspeakers

Port Tuning

KEF's 'Flexible Port Technology' is aptly named because not only is the flare and soft polymer compound of the tubes designed to minimise air turbulence but a choice of two tube lengths are offered to better help 'tune' the speaker's bass to suit different room locations. The soft port tubes are held in position by a circular collar that can be unlocked to provide access, the long tube being nearly twice the length of the short option. As the internal cabinet volume is largely unchanged by the different tubes, and the bass drivers/crossovers remain entirely consistent, the extra mass of air in the long tube delivers a slightly lower Helmholtz resonance of 30Hz [red trace], some 3.5dB lower in amplitude than the 36Hz tuning of the short tube option [black trace]. The port responses are normalised in the inset Graph to better compare their respective bandwidths – note also that KEF has successfully minimised any port or other modes at ~400Hz associated with that tall and narrow cabinet.

The four 165mm alloy-coned bass units operate over a 50-350Hz (–6dB) bandwidth, delivering a diffraction-corrected bass extension of 33Hz (short port) and 29Hz [long port], all re. –6dB/200Hz. The short port offers a slightly 'peakier' bass response with more mid-bass punch in a freestanding location while the long port will better suit a near-wall location where it achieves a smoother and fuller low bass. Audiophiles might also care to experiment with a long port for the lower bass drivers and a short port for the upper pair. PM