L-ACOUSTICS ARCS Manual V2.0
2/13/2003
27
4. SOUND DESIGN
4.1 APPLICATIONS
The art of designing a sound system is a profession in itself and a complete description of all sound
system design aspects is beyond the scope of this manual. If necessary, we recommend the use of a
specialized sound engineer or consultant since
the best products can produce the worst results if
improperly set-up.
In order to get the best results, it is important to follow correct sound design
principles, properly integrate ARCS with subwoofers, use the correct power amplification and use the
correct OEM factory preset.
In general terms, ARCS is primarily intended for medium-scale Front-Of-House (FOH) sound
reinforcement. ARCS is a high-Q design and is capable of producing very high SPL output despite its
compact size. When arrayed, coupling occurs at low and mid frequencies until the frequency is high
enough to enter the "individual" mode where individual waveguides of each enclosure control the
directivity 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 SPL
is directly determined by the Q factor of the HF waveguide. For this reason, the throw of an ARCS
array 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 of
the 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 this
reason it is often desirable to fly the system. However, when ARCS is flown and the audience seating
area begins very close to the stage, it is sometimes necessary to use distributed front-fill speakers (for
example, L-ACOUSTICS MTD108a) or a ground stacked left/right ARCS stereo infill system in order
to 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 be
covered. The horizontal coverage of each enclosure is 22.5° and the total horizontal coverage of the
array is a multiple of 22.5°. For a single row ARCS array, the vertical coverage is asymmetrical,
pro40 degrees by -20 degrees and cabinets can either be flown in the normal orientation (for
up-fill) or inverted (for down-fill). When ARCS is used in a double row configuration, the top row
cabinets are oriented in the normal position for up-fill (+40 degrees) and the bottom row cabinets
inverted for down-fill (-40 degrees). Double row configurations are typically used to improve low
frequency 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 over
the entire operating bandwidth).
With the addition of ARCBUMP, 1- 4 ARCS can be flown horizontally. In this orientation, horizontal
coverage 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 the
offstage direction). Vertical coverage angles are : 22.5, 45, 67.5 and 90 degrees for 1, 2, 3, 4 ARCS
respectively.
Note: Please refer to the ARCS Rigging Reference Charts in Section 5 for a summary of array tilt angles
versus BUMP3, LIFTBAR and ARCBUMP pick points for different array configurations.
SINGLE ROW ARRAYS
An ARCS array behaves as a constant directivity single source with an apparent acoustic center located
at 1.15 m behind the array due to the modular curvature of the radiated wavefront. At lower
frequencies, directivity control occurs at a frequency that varies according to the number of
enclosures. 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 a
single 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
Summary of Contents for ARCS
Page 1: ...Version 2 February 2003 L ACOUSTICS ARCS OPERATOR MANUAL ...
Page 9: ...L ACOUSTICS ARCS Manual V2 0 2 13 2003 8 Figure 3 ARCS System Block Diagram ...
Page 48: ...L ACOUSTICS ARCS Manual V2 0 13 02 03 47 Table 13 ARCS Rigging Reference Chart ...
Page 52: ...L ACOUSTICS ARCS Manual V2 0 13 02 03 51 Figure 26 ARCS line drawing ...
