L-Acoustics V-DOSC, Руководство оператора

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L-ACOUSTICS V-DOSC Manual Version 4 6/29/2005 Page 94 of 158
Selection of the time alignment reference location is always a compromise since the geometric path
difference will vary with position. Time aligning at a distance where the SPL from the ground stacked
subwoofers equals the SPL from the V-DOSC low section is recommended as an optimum
compromise. Horizontally, the reference position should be on-axis or in between the V-DOSC and
subwoofer arrays. Time aligning in the middle is not recommended in order to help reduce centre
build up and one side of the system should be time aligned at a time (FOH L as shown in Fig 71).
Figure 71: Recommended time alignment reference location for flown V-DOSC, ground stacked L/R subwoofers
For ground stacked LCR subwoofer arrays, it is recommended that the L subwoofer array is delayed
with respect C array with the microphone on axis to the L array. Following this, the flown V-DOSC
array should be time aligned with respect to the L array using the techniques outlined in Figure 71.
When subwoofers are ground stacked and physically separated from the flown V-DOSC arrays, the
preferred preset options are: INFRA, 4W or X AUX. For INFRA and 4W presets, crossover points
between sub and low sections are 60 Hz and 80 Hz, respectively. Complementary crossover filtering
for these presets helps to avoid phase problems due to overlapping sub and low section operating
bandwidths so that subwoofers can be operated with positive polarity whether the system is driven in
4-way mode or with aux sub drive. The 4W preset is not recommended for high SPL applications
since less low frequency energy is radiated by the flown V-DOSC system (due to the 80 Hz high pass
filter). In order to benefit from the available resources of the V-DOSC low section, the INFRA preset
is recommended. An additional benefit of the INFRA preset is that time alignment is more forgiving for
a greater part of the audience (due to the longer wavelengths at 60 Hz) and, subjectively, the subs
become more of a delocalized effect due to the lower crossover point.
If more low frequency energy is desired from the flown V-DOSC system, X AUX presets can be used.
For the X AUX preset, the V-DOSC low section is high pass filtered 30 Hz and SB218s are operated
from 25-80 Hz with negative polarity to account for the phase shift that occurs due to the overlap in
the operating bandwidths (i.e., the 24 dB per octave low pass filter for the SB218 generates a phase
shift of 180°). The X AUX preset takes full advantage of V-DOSC low section resources and can be
implemented using Input B / Output 6 for the standard X preset.
V-DOSC 3W or 3WX presets can also be used in conjunction with additional aux sub drive presets for
flown V-DOSC and ground stacked subwoofer configurations. This approach is particularly useful
when implementing delay processed subwoofer arrays, LCR subwoofer arrays or for larger subwoofer
array configurations where it is desirable to dedicate a DSP unit to subwoofer drive for additional
control and flexibility.
The 3WX preset features a 30 Hz high pass filter for the V-DOSC low section combined with
optimized low frequency shelving equalization and aux sub drive can be performed using SB218
DELAY ARC 80 Hz or SB218 LCR 80 Hz presets (subs with negative polarity).The 3W INFRA preset
features a 60 Hz HPF for the V-DOSC low section and SB218 DELAY ARC 60 Hz or SB218 LCR 60
Hz presets are recommended for aux sub drive (subs with positive polarity).