L-Acoustics V-DOSC, Руководство оператора

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L-ACOUSTICS V-DOSC Manual Version 4 6/29/2005 Page 88 of 158
3.2 ACHIEVING OPTIMUM COVERAGE
ARRAY 2004 or SOUNDVISION are convenient simulation tools for optimizing the coverage for a
complete system consisting of multiple V-DOSC arrays and complementary fill systems. Parameters
for each array such as spatial coordinates, azimuth angle (i.e., horizontal panning), number of
enclosures and inter-enclosure angles are entered by the sound designer and individual elements of
the sound design are optimized with respect to the vertical cutview geometry of the audience in
accordance with WST Condition 4.
In the horizontal plane, the displayed isocontours (ARRAY2004) or impact coverage (SOUNDVISION)
should overlap to a certain extent and cover the majority of the audience. For the amount of overlap
see below for a discussion of the tradeoffs between stereo perception versus intelligibility. The
remaining uncovered areas should be covered with fill speakers such as dV-DOSC, ARCS, KUDO or
additional V-DOSC arrays. Additional distributed front fill or stereo infill systems using L-ACOUSTICS
MTD108a, MTD112b, MTD115b, 112XT, 115XT or 115XT HiQ loudspeakers are also highly
effective in complementing V-DOSC system coverage.
3.2.1 THE LEFT/RIGHT CONFIGURATION
Although not the best technical solution, the left/right configuration meets both visual and practical
criteria and is most commonly used. V-DOSC is a dramatic improvement over conventional systems
but, by nature, the stereo imaging of any left/right system is limited for a large part of the audience and
there are compromises with respect to the consistency of tonal balance in the horizontal plane.
The biggest problem for any left/right system is non-uniformity of tonal balance horizontally. Typically,
an excess of low frequency energy builds up in the middle, accompanied by reduced intelligibility. The
net result is that the system sounds bass-heavy or “thick” in the middle, “harsher or more aggressive”
when directly on-axis with one side of the system, and “thin” offstage. These effects are due to the
path length difference interference effects that are inherent in any left/right system which, in turn,
produce frequency- and position-dependent peaks and dips.
Tradeoffs Between Intelligibility and Stereo Imaging
The left/right configuration has the advantage of being able to reproduce effects of spatialization and
localization. The area over which these effects is audible depends on the separation of the two arrays
and the orientation of the left array with respect to the right array, defined by the intersection of the
isocontours for both arrays. The more the arrays are rotated or panned onstage (“toed in”), the
greater the area over which stereo imaging is experienced. The less they are rotated onstage and the
more they are aimed offstage, the less stereo imaging is audible. Typically, for concert applications L/R
arrays are separated 15-20 meters and used at zero degrees or panned 2-5 degrees offstage.
Experience has shown that this provides the best tradeoff between stereo imaging, evenness of
horizontal coverage and reduction of the potential for build up of low frequency and upper mid bass
energy in the centre.
Note: Use of the delta plate rigging accessory provides a convenient way to vary the panning angles of flown
L/R systems and adjust the amount of overlap and stereo imaging.
There are also tradeoffs with respect to intelligibility when aiming arrays. Psychoacoustically, improved
intelligibility is obtained when the isocontours of both arrays do not overlap too much. Provided that
audience coverage is correct, intelligibility is optimal when only one array radiates on a given audience
area. If two arrays are to cover a common area, intelligibility losses result when the distance separating
the two arrays becomes too great. A standard distance of 20 m (65 ft) is acceptable, however, if
greater separation is specified, one should avoid rotating the arrays onstage too much - this
emphasizes arrival time differences between the arrays, thus degrading intelligibilty.
The decision whether to emphasize intelligibility or stereo imaging mainly depends on the application.
For music applications, more overlap is desired and for speech reinforcement less is more
appropriate.