L-Acoustics ARCS Operator's Manual

Contents

L-Acoustics ARCS Operator's Manual Manual pdf 28 page image

L-ACOUSTICS ARCS Manual V2.0 2/13/2003 274. SOUND DESIGN4.1 APPLICATIONSThe art of designing a sound system is a profession in itself and a complete description of all soundsystem design aspects is beyond the scope of this manual. If necessary, we recommend the use of aspecialized sound engineer or consultant since the best products can produce the worst results ifimproperly set-up. In order to get the best results, it is important to follow correct sound designprinciples, properly integrate ARCS with subwoofers, use the correct power amplification and use thecorrect OEM factory preset.In general terms, ARCS is primarily intended for medium-scale Front-Of-House (FOH) soundreinforcement. ARCS is a high-Q design and is capable of producing very high SPL output despite itscompact size. When arrayed, coupling occurs at low and mid frequencies until the frequency is highenough to enter the "individual" mode where individual waveguides of each enclosure control thedirectivity of the emitted wavefront at 22.5∞ horizontal. At frequencies higher than this limit(approximately 2 kHz), the SPL output of the array is limited to that of a single enclosure and the SPLis directly determined by the Q factor of the HF waveguide. For this reason, the throw of an ARCSarray can be considered to be independent of the number of enclosures.Since an ARCS array has constant directivity behavior it is important not to have the very first part ofthe audience too close to the system (i.e., in order not to produce excessive SPLs up close). Ideally,the ratio between the shortest and furthest distance covered should not exceed 1:4 and for thisreason it is often desirable to fly the system. However, when ARCS is flown and the audience seatingarea begins very close to the stage, it is sometimes necessary to use distributed front-fill speakers (forexample, L-ACOUSTICS MTD108a) or a ground stacked left/right ARCS stereo infill system in orderto improve coverage and image localization for the first rows of the audience.ARCS is typically arrayed in a number and configuration based on the geometry of the audience to becovered. The horizontal coverage of each enclosure is 22.5∞ and the total horizontal coverage of thearray is a multiple of 22.5∞. For a single row ARCS array, the vertical coverage is asymmetrical,providing +40 degrees by -20 degrees and cabinets can either be flown in the normal orientation (forup-fill) or inverted (for down-fill). When ARCS is used in a double row configuration, the top rowcabinets are oriented in the normal position for up-fill (+40 degrees) and the bottom row cabinetsinverted for down-fill (-40 degrees). Double row configurations are typically used to improve lowfrequency throw and impact due to the enhanced low frequency coupling obtained since all 15''loudspeakers satisfy WST Condition #2 (acoustic center separation is less than half wavelength overthe entire operating bandwidth).With the addition of ARCBUMP, 1- 4 ARCS can be flown horizontally. In this orientation, horizontalcoverage is 60∞ (asymmetrical) and for L/R FOH applications, ARCS is normally oriented with the 40∞angle directed onstage (i.e., L-ACOUSTICS logos of the left and right enclosures oriented in theoffstage direction). Vertical coverage angles are : 22.5, 45, 67.5 and 90 degrees for 1, 2, 3, 4 ARCSrespectively.Note: Please refer to the ARCS Rigging Reference Charts in Section 5 for a summary of array tilt anglesversus BUMP3, LIFTBAR and ARCBUMP pick points for different array configurations.SINGLE ROW ARRAYSAn ARCS array behaves as a constant directivity single source with an apparent acoustic center locatedat 1.15 m behind the array due to the modular curvature of the radiated wavefront. At lowerfrequencies, directivity control occurs at a frequency that varies according to the number ofenclosures. The larger the array, the lower the frequency where directivity control is obtained.The horizontal coverage is N x 22.5∞ (where N is the number of ARCS) and the vertical coverage of asingle row array is the same as for a single enclosure regardless of the number of ARCS in the array(i.e., 60∞ total : 40∞ up, 20∞ down when the main axis is aimed at 0∞ and the cabinets are in the normal