L-Acoustics ARCS Operator's Manual

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L-Acoustics ARCS Operator's Manual Manual pdf 34 page image

L-ACOUSTICS ARCS Manual V2.0 2/13/2003 33number of ARCS enclosures required for achieving the desired horizontal coverage plus for examiningphysical array location and aiming relative to the main V-DOSC arrays. Since a reduced amount of lowfrequency energy is generated (compared to when V-DOSC is used for offstage fill), the ARCS arraycan be physically located closer to the main V-DOSC arrays than the normally recommended 6-7meters without introducing low frequency interaction problems.Note: Time alignment of complementary fill systems with the main left/right arrays is necessary in order toachieve optimum results. Placing your measurement microphone in a representative location where the filland main system coverage overlaps generally provides a good reference point for time alignment.4.5 DELAY SYSTEMSARCS can be used as a delay system for large audience areas - oriented either horizontally or verticallyaccording to the coverage requirements. The excellent longthrow capability of V-DOSC oftentimeseliminates the need for a delay system, however, some external conditions such as physical obstacles,wind, sound wave refraction due to temperature and humidity gradients or very large distances (>150m) may create the need for a delay system (typically for open-air applications).The use and tuning of delay systems in open-air situations is not straightforward since the correctdelay time setting is typically valid only over a limited area and there are also effects of wind,temperature and humidity to consider. However, there are a few principles that should be appliedwhen installing delay systems:1) Over-delaying up to 15 ms is acceptable due to the Haas effect. Greater than 15 ms is notacceptable since the delayed sound will be perceived as an echo behind the main signal. Timealignment of delays should be made using a measurement point on the axis of the reference sourceand the delayed source. If the delay time setting is such that the two sound waves arrive at the sametime on-axis, the reference source will be slightly ahead of the delayed source at any other locationoff-axis. For some applications (speech), it is advised to under-delay in order to optimize the off-axisintelligibility and clarity behind the delayed system (i.e., closer to the stage).2) Spread different sources, with different delayed waves, instead of grouping them in a single location.This allows for broader coverage by the delayed sources and produces more homogeneous SPL overthe delay-covered area.3) Distributed delay positions should be along a circular arc of constant radius, centered at the stage.Time domain-based measurement equipment is essential for setting delay times (for example,MLSAA, WINMLS, TEF, SMAART or SPECTRAFOO). Alternatively, Bushnell Yardage Pro rangefinderbinoculars can provide a good starting point by simply measuring the distance from the delay locationto the main system. For delay system design, ARRAY software can be used to provide a quickreference, i.e., V-DOSC can be deliberately focused to provide a 10-20 meter overlap with thecoverage provided by the delay system. The ARRAY software then gives an indication as to physicaldelay tower locations and required time delays.051015202530-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115Figure 19: ARRAY cutview simulation of an ARCS FOH system with delays. The main L/R system consists of 8-10 ARCS per side in a double row configuration with 4 ARCS per side ground stacked for stereo infill. Delayrings are located at 45 and 75 meters and the exact number of delay positions per ring will depend on the planview of the audience and the amount of horizontal coverage required.