Loudspeakers

With the LPF disabled (LFE Mode ‘Active’), the sub’s working bandpass is a maximum 17Hz-205Hz (–6dB re. 100Hz) right down to a narrow 15Hz-93Hz with the LPF set to the lowest 30Hz. The infra-bass roll-off acts below 20Hz and is essentially unchanged by the LPF setting [Graph 1, below] – this appears to be a gentle third-order (18dB/octave) slope reaching 15Hz (–6dB re. 100Hz). This benefits not only LF extension but also minimises the inevitable group delay – and phase distortion – back in the low audioband. In this instance the latency is 6msec and the max. in-band group delay is 33msec/20Hz (80Hz/12dB slope). Also, the impulse decay time is a moderate 43msec (re. –20dB) – acceptable, given the moving mass of the driver [see Graph 2].

Lower bass may be achieved than indicated by the ground plane responses [see Graph 1] if the SB17 is parked against a wall or – with great care – a corner. The intermediate LPF settings yield 16Hz-85Hz (60Hz), 17Hz-110Hz (90Hz) and 17Hz-125Hz (120Hz, all re. 12dB LPF slope). Relaxing the slope to a first-order 6dB widens this to 15Hz-84Hz (30Hz LPF), 16Hz-111Hz (60Hz), 16Hz-126Hz (90Hz) and 17Hz-137Hz (120Hz). The steepest 24dB/oct slope gives a narrow 15Hz-37Hz (30Hz), 16Hz-73Hz (60Hz), 17Hz-97Hz (90Hz) and 18Hz-124Hz (120Hz). SVS’s Room Gain compensation acts at 25Hz, 31Hz & 40Hz, reducing the SPL by 6dB (ie one boundary) at the selected ‘compensation frequency’. The infra-bass roll-off is unchanged but level and extension are reduced, ie a 40Hz compensation (re. 120Hz/12dB) realises a reduced 39Hz-136Hz bandpass (as opposed to 17Hz-125Hz). Finally, distortion is a low <0.2% (20Hz-100Hz, re. 90dB SPL) and only finally climbs to 1%/20Hz at 109dB SPL/1m. PM