Elements Of Sound Design; Multiple Array Concepts; Reducing Array Interaction; Achieving Optimum Coverage - L-Acoustics dV-DOSC Operator's Manual

3. ELEMENTS OF SOUND DESIGN

3.1 MULTIPLE ARRAY CONCEPTS

Reducing Array Interaction

It is well known that the collective radiation of sound by a number of loudspeakers located close to
each other results in interference that creates frequency-dependent directivity lobes. The only
coherent way to couple loudspeakers is to meet Wavefront Sculpture Technology criteria, which,
for the case of dV-DOSC is met in the vertical domain.
When the horizontal coverage of a dV-DOSC array (120° nominal, 100° effective) is not sufficient,
the solution is not to place a second array directly beside the first one. The correct approach is to
utilize a second array which is focused on another portion of the audience and spaced at least 6-7
meters (approximately 20 ft) away from the first array.
Given this separation, interference only occurs in the low frequency range and there are no audible
intelligibility losses for two reasons: 1) the first main cancellation is shifted lower in frequency
(example, 24 Hz for 2 arrays of the same size, spaced 7 metres) and tends to be masked or filled in
by room reverberation; 2) by focussing the arrays at different panning angles, comb filtering
interaction is lessened since their overlap region is reduced. In addition, the ear cannot resolve
tightly spaced comb filtering notches at higher frequencies throughout the overlap region.
The array closest to the stage is usually the larger of the two arrays. This array is considered as the
time reference and any other array is delayed with respect to it. This is valid for arrays fed with the
same signal (in a stereo configuration, it is obvious that the left array is not delayed with respect to
the right one or vice-versa).
Experience has shown that this is a very flexible approach that can cover any type of audience. An
additional advantage of multiple arrays is improved resistance to wind effects in open-air situations.
Another benefit is improved perception of stereo effects throughout the audience area – something
which should not be limited to just the mix position (i.e., arrays can be run in cross-panned stereo
with L-L (right), L (left), R (right) and R-R (left)).
Beyond the basic solution of coverage problems, multiple source arrays open up many possibilities
for creating a spatial soundscape, thus providing a powerful tool for sound design and creativity.

Achieving Optimum Coverage

Using the isocontour drawn on a blueprint or the data provided in ARRAY 2000 (H-ISOCONTOUR),
it is easy to achieve correct horizontal coverage for a complete system consisting of multiple V-
DOSC and/or dV-DOSC arrays. Parameters for each array such as spatial coordinates, axial direction
and output level are first chosen by the sound designer and entered in the ARRAY 2000 spreadsheet
with respect to the basic geometry of the audience.
The displayed horizontal isocontours should overlap to a certain extent and cover the majority of
the audience. The amount of overlap will depend on the tradeoffs between stereo perception and
intelligibility. The remaining areas should be covered with fill speakers such as ARCS, MTD115a,
MTD112, MTD108a or EX112 loudspeakers.
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