Loudspeakers

Measured on its centre axis, the forward response [see Graph 1, below] is necessarily compromised by the multitude of acoustic path lengths reaching the microphone from different positions across the curved surface of the electrostatic panel. The high-Q peaks and notches visible in Graph 1 are integrated out, to a degree, with increased listening distance although the complex low-level resonances [see CSD plot, Graph 2] are more of a fixture. In practice while the response uniformity improves from ±6.2dB at 1m [blue trace] to ±4.8dB at 2m [black/red traces, and principally from 500Hz-3kHz] this would still be wide of the mark for a conventional moving-coil tower. Nevertheless, the general response trend for the EM-ESL X remains fairly 'flat' from 500Hz-5kHz beyond which the treble output falls away by ~9dB from 5kHz-20kHz. Despite all this 'uncertainty' the pair matching is remarkably fine at 1.7dB (500Hz-20kHz) even if the overall sensitivity is slightly short of MartinLogan's 91dB specification at 88.8dB/1kHz and 89.6dB/500Hz-8kHz.

The front 200mm paper-coned woofer has a 54Hz-320Hz bandwidth, the rear a somewhat narrower 48Hz-190Hz (both re. –6dB) with a 'step' at 155Hz. This, coupled with the downward-firing reflex port with its broad 13Hz-81Hz output, delivers a corrected bass extension of 38Hz [–6dB re. 200Hz, green shaded area Graph 1]. This is generous for the limited enclosure volume, albeit achieved with a low 2.9ohm min. load (4ohm nominal) through the moving-coil section at 30Hz and via the panel at 720Hz. In both instances the impedance phase holds to within ±17o, but the load remains sub-6ohm from 13Hz-1.17kHz. PM