L-Acoustics V-DOSC, Operator'S Manual

Page: 54 / 158

L-ACOUSTICS V-DOSC Manual Version 4 6/29/2005 Page 54 of 158
4-WAY PRESETS
SUBWOOFER TIME ALIGNMENT RECOMMENDATIONS
As of the Version 7 preset library release, sub/low sections have been “pre-aligned” for 4-way and 5-
way presets in a closely coupled measurement configuration, i.e., ground plane measurements were
conducted on a stack of 3 V-DOSC + 2 SB218 and all sub channel delays were pre-aligned for this
configuration to obtain optimum summation. Therefore, when V-DOSC is flown and subs are ground
stacked, all that is required is to measure the geometric physical path difference (at your reference
point of choice) and add this to the standard pre-aligned sub delay. If using Bushnell Rangefinders to
measure the path difference, the accuracy corresponds to +/- 1 meter so the geometric starting point
can be varied by +/- 3 msec to verify optimum summation.
Pre-alignment allows for quick and easy subwoofer time alignment for those who don’t have the
measurement gear required to measure impulse responses. If you have the ability to measure impulse
response, refer to the following figures for individual presets as a reference for time alignment.
Basically, when you look at the separate impulse responses for sub and low sections, there is a “sine
wave” signature that needs to be aligned.
SUB/LOW GAIN SCALING PROCEDURES
The Version 7 preset release has been optimized for a 1.5 : 1 cabinet ratio of V-DOSC : SB218 (for
example, 3:2, 6:4, 9:6, 12:8, 15:10). As a starting point, output channel gains for a 3:2 V-DOSC:SB218
cabinet ratio are as follows (HI presets):
BAND / PRESET X X AUX INFRA 4W
SUB +4 dB +6 dB +6 dB +6 dB
LOW 0 dB 0 dB +2 dB +2 dB
MID -5 dB -5 dB -5 dB -5 dB
HIGH -5 dB -5 dB -5 dB -5 dB
Recommended gain scaling procedures for different cabinet ratios are summarized as follows:
2:1 V-DOSC:SB218 ratio scale subwoofer gain by +2 dB (or low section by -2 dB)
1.5:1 V-DOSC:SB218 ratio standard gains
1:1 V-DOSC:SB218 ratio scale low gain by +4 dB
Following this gain scaling procedure according to cabinet ratio will provide a consistent sub/low
spectral contour for all 4-way presets. The mid and high sections should then be scaled up or down
equally according to the size of the array in order to compensate for low frequency coupling effects
and to provide the overall desired tonal balance (see also Chapter 5 re: tuning).
SUBWOOFER PRESETS (DELAY ARC, LCR)
For large format configurations, a useful technique for processing a central ground-stacked horizontal
line array of subwoofers is to use delay processing to electronically arc the subwoofer array. Two
presets are provided with 60 Hz (SB218 = INFRA mode) and 80 Hz (SB218 = 4W or X AUX mode)
crossover points.
Another useful technique is to create a Left/Centre/Right (LCR) array of subwoofers where each block
has the same number of subwoofers. For the case of the LCR sub array, L/R arrays can be oriented at
45 degrees offstage and instead of a single buildup between L/R arrays (as for L/R split stacks), with an
LCR array there are two ''mini buildups'' between L/C and C/R that help to smooth out the centre
build up that is obtained with L/R configurations. Two presets are provided with 60 Hz (SB218 =
INFRA mode) and 80 Hz (SB218 = 4W or X AUX mode) crossover points and channel assignments
that are suitable for implementing LCR sub arrays.