L-ACOUSTICS ARCS Manual V2.0
2/13/2003
5
2) Frequency: The step or source separation, defined as the distance between the acoustic centers of the
individual sources, is smaller than half the wavelength at all frequencies over the bandwidth of operation
(generally, this criteria is satisfied at lower frequencies since the wavelengths are sufficiently large).
These two conditions form the basis of Wavefront Sculpture Technology
®
(WST).
Additional conditions were published in the AES preprint ''Wavefront Sculpture Technology'' that was
presented at the 111
th
Convention, NYC, 2001 (preprint 5488). The first two WST conditions were
re-derived (based on an intuitive approach using Fresnel analysis) and it was shown that:
3) Deviation from the ideal, target wavefront (flat or curved) must be less than a quarter wavelength at the
highest operating frequency (this corresponds to less than 5 mm curvature at 16 kHz)
4) For curved arrays, enclosure tilt angles should vary in inverse proportion to the listener distance
(geometrically this is equivalent to shaping variable curvature arrays to provide equal spacing of individual
element impact zones)
5) Limits exist concerning the size of each enclosure, the minimum allowed listener distance and the
relative angles that are allowed between enclosures.
At higher frequencies, the only way to couple individual sound sources is to make them behave like a
single source. Practically, this means creating a
continuous
wavefront, which can be achieved using
individual sound sources only if they meet the requirements defined by WST Conditions 1 and 3. To
create a continuous wavefront, the total area of the discontinuities between adjacent individual
wavefronts must be less than 20% of the total surface area of the two wavefronts
and
the deviation of
any point on the wavefront surface with respect to the location of the theoretically equivalent
continuous wavefront must be less than a quarter wavelength of the highest frequency to be
reproduced.
The key to satisfying WST criteria at higher frequencies is a specific waveguide that is used to load a
conventional compression driver. This DOSC
®
waveguide was invented by Dr. Christian Heil and is
patented world-wide. DOSC stands for ”Diffuseur d’Onde Sonore Cylindrique” – in English this
means Cylindrical Sound Wave Generator.
Essentially, the DOSC waveguide permits fulfilment of the 1
st
and 3
rd
WST conditions at higher
frequencies. For traditional horn-loaded systems, coherent summation is not possible at higher
frequencies since the wavelength becomes progressively smaller than the physical separation between
horn and driver assemblies and neither of the first two WST conditions can be satisfied.
c) The ARCS
®
Sound Reinforcement System
The first application of Wavefront Sculpture Technology (WST) is the world-famous V-DOSC
®
- a
system that is capable of generating cylindrical wavefronts and meeting WST coupling conditions for
angles of 0° to 5° between adjacent boxes. Among other features, V-DOSC has been established as
the sound reinforcement system providing the longest throw ever.
Requirements for smaller array configurations and shorter throw distances, but with the same quality
standards as set by V-DOSC, led to the design of ARCS. Since ARCS generates a modular, curved
wavefront, ARCS stands for "Arrayable Radial Coherent System". While V-DOSC uses variable
curvature arrays to perform wavefront sculpture in the vertical plane, ARCS operates in the horizontal
(or vertical) plane and generates a modular, constant curvature wavefront with a radius of wavefront
curvature corresponding to 1.15 meters.
The patented DOSC waveguide designed exclusively for ARCS loads a compression driver that is
operated from 900 - 20k Hz. This waveguide produces a radiated wavefront that covers the total
width of the enclosure and has an arc's shape of 22.5°. Individual radiated wavefronts are curved
rectangular strips that match the trapezoidal angle of each ARCS enclosure and, as a result, the
wavefront radiated at high frequencies by an ARCS array is continuous with an arc's shape that is equal
to the N*22.5° (where N is the number of enclosures). For example, four ARCS enclosures provide a
horizontal coverage angle of 90°.
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 ...
