L-Acoustics V-DOSC, Operator'S Manual

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L-ACOUSTICS V-DOSC Manual Version 4 6/29/2005 Page 95 of 158
3.4.2 Physically Coupled Subwoofers
When subwoofers are physically coupled with the V-DOSC array (flown offstage or stacked
underneath with minimum physical separation) the preferred preset options are: X, INFRA or 4W.
For these configurations, the system is normally operated in 4-way mode with the input signal for the
subwoofers identical to that of the V-DOSC array. The X preset is recommended since SB218
subwoofers and the V-DOSC low section have the same operating bandwidth (30-200 Hz) and using
identical crossover points help to avoid phase shift cancellation problems (note: additional equalization
for the subwoofer section performed in the X preset provides an effective 120 Hz low pass filter for
the subwoofers – see Fig. 40).
Flown subwoofers
Subwoofers stacked as a vertical extension
Figure 72: Physically coupled subwoofer configurations
Optimum coupling between subwoofer and V-DOSC arrays is achieved by keeping the SB218 array
physically close to the V-DOSC array. Two configurations are possible:
1) Fly the SB218 array on the offstage side, less than 3 metres from the V-DOSC array, axis-to-axis
The benefits of flown subwoofers include:
•
Improved low frequency summation, impact and throw.
•
Improved time alignment since the physical path length difference problem of ground stacked
subwoofers versus flown V-DOSC is no longer an issue. Overall, this improves low frequency
summation and coherency.
•
Elimination of local low frequency buildup for the audience down front in the first few rows.
Adding several ground stacked subwoofers per side or a centre position will provide sufficient low
end impact for the first 15-20 metres (see Section 3.4.3).
•
Cleaner staging and better audience sightlines.
2) Stack the SB218 array directly underneath or beside (offstage) the V-DOSC array
•
When subs are stacked in a column underneath the V-DOSC array with minimum physical
separation, extended vertical pattern control is obtained at very low frequencies
•
Improved coupling is obtained since there is almost no discontinuity in low frequency radiation
from the top of the array to the ground
•
This configuration is recommended for flat, open air applications since extended vertical
pattern control and coherent coupling provides improved throw at lower frequencies.
NOTE: For the X preset, subwoofers sound different than most sound engineers would expect due to the
27-200 Hz operating bandwidth. Listening to the system band-by-band can be misleading, however, the
collective performance of all speakers should produce incomparable low frequency far field projection.