L-Acoustics ARCS Operator's Manual

Contents

L-Acoustics ARCS Operator's Manual Manual pdf 29 page image

L-ACOUSTICS ARCS Manual V2.0 2/13/2003 28orientation). The orientation of the ARCS enclosures (normal or inverted) will depend on the trimheight of the array (flown or stacked) and the audience geometry. In most cases, there is no need totilt a flown array - if tilt is required, it is typically by a much smaller angle than is required forsymmetrically radiating systems (see also ARRAY AIMING).DOUBLE ROW ARRAYSFor larger scale applications with expanded vertical coverage requirements, ARCS is used in a doublerow configuration with top row cabinets oriented in the normal position for up-fill and the bottomrow cabinets inverted for down-fill. When arrayed in this manner (logos together as a quick visualreference), all 15'' loudspeakers satisfy Wavefront Sculpture Technology Criteria and couple over theirentire operating bandwidth, thus providing maximum low frequency impact and throw due toenhanced directivity control at lower frequencies. The HF sections are oriented with +40/-20degrees coverage for the top row and +20/-40 degrees for the bottom row providing an overallvertical coverage angle of 80 degrees total. Given the physical separation of the HF sections, the 20degree coverage angles of the top and bottom sections do not start to interact until a distance of 10meters and interference effects at greater distances tend to be masked by room reverberation and thepsychoacoustics of tightly spaced comb filtering at higher frequencies which is difficult for the ear toresolve. However, to help minimize this interaction it can be useful to apply a separate time delay tothe bottom row of ARCS enclosures so that the bottom row is time aligned with respect to the toprow at the FOH mix position (or approximately 30 metres from the system as a reference point).4.2 ARRAY AIMINGThe first task is to map the coverage of an ARCS array in the vertical plane (i.e., section cutview) inorder to see how it matches the audience area to be covered. L-ACOUSTICS' proprietary ARRAYsoftware is useful for this purpose ñ although specific ARCS modeling is not included, the followingprocedure will give an estimate as to the vertical coverage:Enter: X1, Z1, X2, Z2 in the Cut-view 1 cells (X = range, Z = elevation) to define to a section profile ofthe given audience geometry (see the V-DOSC or dV-DOSC manuals for further details)Enter: 3 for ì# of ElementsîEnter: 40 for ì#1 to nextî for the normal orientation (or 20 for ì#1 to nextî for inverted)Enter: 20 for ì#2 to nextî for the normal orientation (or 40 for ì#2 to nextî for inverted)Adjust: ìBumper elevationî, ìAutofocus Adjustî parameters until audience coverage is satisfactoryRefer to: ìSiteî for ì#2 to nextî and the ARCS Rigging Reference Chart in Section 4 to determine theappropriate BUMP3 / LIFTBAR pick point.Refer to: ìBumper elevationî to determine the system trim height.When ARCS is used in the vertical orientation, it is easy to visually check the horizontal coverage of anARCS array since the coverage area is effectively defined by the outer walls of the outer cabinets ofthe array. Basically, if you can see the outside cabinet wall (onstage or offstage), you are outside of thecoverage pattern.Note: A useful technique in theatres or conference rooms is to align the outside wall of the offstage ARCSenclosure parallel to the wall surface in order to avoid wall reflections.