Loudspeakers

With its LPF disabled, the D15s’ working bandpass is a maximum 18Hz-250Hz (–6dB re. 50Hz) with a short 3msec latency and a maximum in-band group delay of 28msec/20Hz. Also, the impulse decay time is a very swift 19msec (re. –20dB) – impressive given the moving mass of the driver. With the most extreme 30Hz/24dB low-pass setting, the bandpass squeezes to 15Hz-38Hz but with an increased 5.5msec latency, a protracted impulse decay of 110msec and 54msec group delay at 20Hz.

Set to ‘Big Room’ mode, with a default 80Hz/12dB slope, the bandwidth relaxes to 18Hz-100Hz (–6dB re. 50Hz), group delay is 38msec/20Hz and decay time settles out to 47msec [see Graph 2]. Switching to THX mode reduces bass output by –3.5dB/20Hz versus the ‘Big Room’ setting, decreasing the impulse decay time to 40msec (re. –20dB) and group delay to 35msec/20Hz. However, the ‘Small Room’ option invokes a gentler 2nd-order roll-off with a reduction in low frequency phase distortion – and arguably improved sound – as group delay is reduced further to 27msec/20Hz and the decay to 30msec.

The intermediate LPF settings yield 15Hz-54Hz (30Hz LPF), 17Hz-81Hz (60Hz), 18Hz-110Hz (90Hz) and 18Hz-135Hz (120Hz, all re. 12dB slope). Relaxing the slope to a first-order 6dB widens this to 15Hz-87Hz (30Hz LPF), 17Hz-115Hz (60Hz), 17Hz-132Hz (90Hz) and 18Hz-142Hz (120Hz). The steepest 24dB/oct slope gives a narrower 15Hz-38Hz (30Hz), 16Hz-73Hz (60Hz), 17Hz-99Hz (90Hz) and 18Hz-129Hz (120Hz). Finally, while distortion reaches 1.5% at 20Hz/90dB/1m SPL – this is ‘only’ a 380mm driver after all (!) – it swiftly drops to <0.1% above 35Hz. This is a powerful and versatile sub. PM