L-Acoustics V-DOSC, Руководство оператора

Страница: 90 / 158

L-ACOUSTICS V-DOSC Manual Version 4 6/29/2005 Page 90 of 158
3.3 MULTIPLE ARRAY CONCEPTS
When the horizontal coverage of a V-DOSC array (90° nominal, 70° effective) is insufficient, it is not
recommended to place a second array directly beside the first one (see Appendix 1 for further
details). The correct approach is to utilize a second array which is focused on another portion of the
audience (typically at 45° - 70° relative to the first array) and spaced at least 6-7 meters (approximately
20 ft) from the first array.
Figure 66: Generic rigging plot for a V-DOSC system consisting of main L/R FOH and LL/RR offstage fill arrays
Given this separation, interference only occurs in the low frequency range and there are no audible
intelligibility losses for the following reasons: 1) the first octave-wide comb filtering cancellation is
shifted lower in frequency outside the V-DOSC low section’s operating bandwidth, for example, 24
Hz for two arrays of the same size, spaced 7 metres; 2) low frequency cancellations from 50-200 Hz
tend to be masked or “filled in” by room reverberation; and 3) the ear cannot resolve tightly-spaced
comb filtering notches at higher frequencies throughout the overlap region of the two arrays.
In addition, by focussing main and offstage fill arrays at different panning angles, audible comb filtering
interaction is lessened since the overlap region between the two arrays is reduced. In some situations,
more overlap may be desirable and cross-panning arrays will help provide stereo to a greater portion
of the audience while de-correlating the signals between adjacent arrays to further reduce audible
interference effects, i.e., arrays can be run in cross-panned stereo and fed as follows: L-L (right
program signal), L (left program signal), R (right program) and R-R (left program).
The main L/R FOH arrays are normally physically larger than the LL/RR offstage fill arrays and act as
the reference for time alignment. Typically, a measurement microphone is located in the overlap
region of the L and LL arrays and the LL array is delayed with respect to the L array (same for the RR
versus the R array). To geometrically improve time alignment in the overlap region between the main
and offstage arrays, the location of the offstage array should follow the arc of a circle with the radius of
the circle at upstage center as shown in Figure 67.
Note: This sound design approach is similar to distributed sound reinforcement using coaxial loudspeakers,
i.e., separating V-DOSC arrays in a manner so that desired audience coverage is achieved while the effects
of audible interference are reduced. For more details on the benefits of coaxial loudspeaker technology and
distributed sound design techniques, please refer to the MTD or XT User Manuals available for download
on:
www.l-acoustics.com