Loudspeakers

KEF's claim of 90dB sensitivity for the R11 is just confirmed by our measured pink noise figure of 89.5dB, although our 'music' result is a little lower at 89.2dB. This is achieved, gratifyingly, without making the R11 difficult to drive. Although KEF specifies a nominal 8ohm impedance, which doesn't square with its quoted 3.2ohm minimum, the R11 nevertheless exercises unusually tight control over its impedance phase angles. In concert with our measured minimum impedance of 3.5ohm – a little higher than KEF specifies – this results in a minimum EPDR (equivalent peak dissipation resistance) of 2.2ohm at a high 7.2kHz, about half an ohm higher than we typically measure from competitors. Other dips to 2.3ohm at 1kHz and 2.4ohm at 82Hz complicate the picture but this clearly isn't a design where impedance is considered to be the amplifier designer's problem.

Forward frequency responses for the review pair, measured at 1m on the tweeter axis, indicate a trend that's admirably flat but for a suckout between 900Hz and 3kHz. This is common to both speakers but more prominent in one of them [see Graph 1]. Even so, the response errors of ±2.3dB and ±2.7dB, respectively, are good results although the pair matching error over the same 200Hz-20kHz frequency range is high at ±1.9dB. This is sufficiently out of line with other KEF speakers we've measured in recent years that we suspect one speaker of this well-run-in demo pair [red trace, Graph 1] may be out of spec. Otherwise, bass extension – determined by diffraction-corrected nearfield measurement – is par for the course at 51Hz (–6dB re. 200Hz) while only some very low-level treble resonances mar what otherwise is a clean CSD waterfall [see Graph 2]. KH