Loudspeakers

Measured on the centre axis of the DPC array the S4b's forward response is marginally downtilted in trend before peaking at 10kHz and then dipping steeply (–7dB/20.6kHz) just prior to the beryllium dome's primary resonance at a relatively low 23.4kHz [see Graph 1]. The undulations through mid, presence and treble – also seen as mild driver resonances [Graph 2] – yield response errors of ±3.1dB and ±3.2dB, respectively [the dip at 3-5kHz is slightly exaggerated by the perforated metal grilles; blue trace], while pair matching is excellent at 0.6dB (200Hz-20kHz). Perlisten's modest 85.4dB sensitivity rating for the S4b is precisely met in practice at 85.7dB (1kHz) and 85.4dB (500Hz-8kHz), figures that are not unreasonable for this modestly-proportioned, sealed enclosure even though THD necessarily increases at HF (~3%/10kHz re. 90dB SPL).

Amplifier loading is still tough given the limited sensitivity, with Perlisten's 3.2ohm minimum rating met, again, on test at 155Hz and its impedance modulus remaining sub-4ohm from 100Hz-525Hz. The toughest reactive load occurs in the bass at 106Hz where the EPDR drops to 1.24ohm, and treble where the EPDR is 1.66ohm/20kHz. But what of bass heft? While the alignment sees a bass peak of 28ohm/49Hz, the output of the 180mm Textreme TPCD woofer peaks at 140Hz with a 48-830Hz bandwidth (–6dB). The 'acoustic suspension' loading offers a gentle (between 1st/2nd-order) bass roll-off [green shaded area, Graph 1] and a diffraction-corrected extension of 55Hz (–6dB re. 200Hz), although boundary reinforcement will produce deeper bass in-room. PM