L-Acoustics V-DOSC, Руководство оператора

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L-ACOUSTICS V-DOSC Manual Version 2.00 29/06/05 V-DOSC MANUAL V4 0605.doc 64/158
2.2 COVERAGE IN THE VERTICAL PLANE
Flat V-DOSC Array
Flying or stacking V-DOSC enclosures with no angular spacing between enclosures produces a flat
array that behaves acoustically as a continuous, isophasic line source that radiates a cylindrical
wavefront. The cylindrical wavefront expands in the horizontal dimension only and is defined by the
section of a vertical cylinder over a given distance. The height of this section corresponds to the height
of the array (defined by the top wall of the top enclosure and the bottom wall of the bottom
enclosure) and the coverage angle corresponds to the -6 dB horizontal coverage angle of V-DOSC
(try to visualize a 90° cheese wedge or a piece of cake…)
According to Fresnel analysis, a cylindrical wavefront is radiated by a line source array over a certain
distance and then transforms into a spherical wavefront. In spherical mode, the wavefront expands in
two dimensions, thus producing a SPL attenuation of 6 dB with doubling of distance. In cylindrical
mode, the wavefront expands linearly with distance in the horizontal plane only, thus producing only 3
dB of attenuation when doubling the distance. The boundary between cylindrical and spherical
wavefront propagation regions depends on the frequency and length of the line source (see
Appendices 5 and 6 for more details).
Since V-DOSC is, in essence, more efficient at projecting HF energy than LF, the net result is that for
large distances, the tonal balance is progressively tilted by a HF enhancement. For longer throw
distances, this tilt in tonal balance is offset by air absorption in open air situations and by both building
material absorption and air absorption indoors, resulting in spectrally-balanced sound over the largest
area possible. This is an important benefit of V-DOSC and WST since both SPL and tonal balance are
more even with distance.
Since the flat array configuration maximizes energy and intelligibility with distance, it should be used
for long throw applications or in reverberant rooms. It is also common to use a flat array section at
the top of a variable curvature array for improved throw in arena and stadium installations. In some
cases, the upper enclosures of flown V-DOSC arrays are ratchet strapped together in order to
provide such a flat long throw section.
Curved V-DOSC Array
A curved V-DOSC array (stacked or flown) is obtained by using angle straps to provide the desired
angle between enclosures. To maintain the correct angles between enclosures, spacer blocks can be
inserted between adjacent enclosures or, alternatively, rear ratchet straps can be used.
If the angle between two adjacent V-DOSC enclosures is smaller than 5.5°, WST criteria are satisfied
and the array behaves like a continuous, curved radiating ribbon. If the angle between enclosures
exceeds 5.5°, WST criteria are no longer valid over the entire audio frequency range. Practically, a
larger angle produces neither desirable nor predictable results - enclosures radiate individually and the
benefits of collective coupling are lost (this is why angle straps are available only up to 5.5°).
There are two types of curved V-DOSC array: constant curvature and variable curvature. For the first
case, the angle between all adjacent enclosures is constant while for the second case, it varies within
the defined range of 0° to 5.5°.