Loudspeakers

With its line/digital inputs and fully integrated Class AB and Class D amplifiers, KEF's LS60 Wireless has no meaningful 'sensitivity' that might be compared with a standard passive loudspeaker. Neither does it have any meaningful 'impedance' – the internal amplifiers are certainly driving a reactive load (the Uni-Q and bass units) but are direct-coupled – there is no passive crossover here – and cannot be swapped out for amplifiers of the user's own choosing. The forward responses plotted here [with all eq. adjustments defeated, see Graph 1 below] are only arbitrarily referenced to 90dB SPL/1kHz but show a strong upper bass and gently declining mid/presence. The 4.5dB kick upwards between 12kHz-18kHz is largely responsible for the ±2.5dB and ±2.3dB response errors, but pair matching is a tight 0.9dB from 800Hz-16kHz. The sharp breakup of the Uni-Q dome – just inside the 96kHz sampling bandwidth – at 44.8kHz (+4dB more vigorous in one speaker, and ~14dB higher than the mean midband level) is revealed here in addition to some mild response ripples between 500Hz-1.5kHz. Both are visible in the CSD waterfall [see Graph 2], revealing the associated resonances, but the band from 2-20kHz is evidently very clean indeed, courtesy of MAT.

The venting up via the plinth and out from the rear of the connection panel is for cooling purposes only, not for bass loading or tuning. In fact the two pairs of 135mm 'Uni-Core Force Cancelling' woofers work into a sealed enclosure, offering a 30Hz-380Hz bandwidth (–6dB) and a combined, diffraction-corrected bass extension of 34Hz. This is better (lower) than might be achieved from a purely passive loudspeaker of similar complement and dimensions, but that's just one advantage of KEF's actively-driven, DSP-governed bass tuning. Through-speaker latency is ~15msec while harmonic distortion is a reasonably uniform 0.3-0.5% (100Hz-10kHz re. 96dB SPL) – another benefit of this sophisticated digital/active configuration. PM