L-Acoustics V-DOSC, Operator'S Manual

Page: 107 / 158

L-ACOUSTICS V-DOSC Manual Version 4 6/29/2005 Page 107 of 158
3.6.3 DELAY SYSTEMS
The excellent long throw capability of V-DOSC often eliminates the need for a delay system and
allows the FOH mix position to be located at distances of up to 65 metres for improved audience
sightlines. However, factors such physical obstacles, wind, sound wave refraction due to temperature
and humidity gradients or very large distances (>120 m) may create the need for a delay system.
Good delay system candidates include V-DOSC, dV-DOSC or KUDO and typically a 4 array FOH
system (LL, L, R, RR) in conjunction with 3-4 delay positions located at approximately 80-100 metres
will provide coverage up to 150 metres or more. The exact number of delay rings and delay positions
per ring will depend on the overall throw distance and horizontal coverage requirements.
Time alignment and tuning of delay systems in open-air situations is not straightforward since the
correct delay time setting is typically valid over a limited area and there are also the effects of wind,
temperature and humidity to consider. Despite these variables, there are a few guidelines that should
be followed when installing delay systems:
1) Distributed delays should be positioned along an arc of constant radius (centered at the stage) in
order to geometrically optimize time alignment throughout the coverage region of the delay system.
2) Delay systems should be focused to provide approximately 10-20 meters overlap with main system
coverage in order to optimize the transition between the main system and the delay. For example,
main L/R V-DOSC arrays can be focused to provide coverage up to 120 metres and delay positions
installed at 90 metres and focused to provide coverage from 100-150 metres.
3) Time alignment of delays should be performed at a measurement point located on the axis of the
delayed source and the reference source. If the delay time is set so that the two sound waves arrive at
the same time on-axis, the reference source will be slightly ahead of the delayed source at off-axis
locations, providing proper image localization towards the stage (see also 1).
4) Over-delaying up to 15 ms is acceptable due to the Haas precedence effect, greater than 15 ms is
not acceptable since the delayed sound will be perceived as an echo with respect to the main signal.
5) For speech reinforcement, it may be necessary to under-delay in order to optimize the off-axis
intelligibility and clarity for the audience seated behind the delay system (i.e., towards the stage).
6) Time domain-based measurement equipment is essential for setting delay times (for example,
MLSSA or WinMLS). Bushnell Yardage Pro rangefinder binoculars can provide a good starting point by
simply measuring the distance from the delay location to the reference source.
Figure 87 shows an outdoor festival system example for an audience area of 150 metres deep by 200
metres wide. The main L/R system consists of 16 V-DOSC per side and there are 12 V-DOSC for the
LL/RR arrays. Four delay positions of 9 V-DOSC each are located on a circular radius 80 metres from
the stage. The main L/R system is focused to 120 meters, LL/RR are focused to 110 metres and delay
system coverage is from 100-150 meters.
Figure 87: SOUNDVISION simulation for a LL/L/R/RR V-DOSC FOH system with 4 delay positions