1352 Chapter 35
- The desired directional effect is given only in a range
below the critical frequency, whereas above that
frequency there occur additional secondary maxima. - The directivity is frequency-dependent—front-to-ran-
dom factor J of the main maximum |5.8 lf (l is the
length of the column in m and f the frequency in
kHz).^16 - The directivity increase does not only occur in the
directivity domain, but also, owing to the distances of
the individual loudspeakers, in the scattering domain,
so the column is losing directivity at high frequencies.
All these frequency-dependent properties of the
loudspeaker lines involve the possibility for timbre
changes to occur over the width and depth of the
covered auditory. In order to eliminate or limit this
drawback, the lines are often subdivided in the upper
frequency range. This is mostly accomplished by
curving the line “bananalike” or like a so-called J-
Array. Alternatively individual elements can be rotated
slightly off-axis in the horizontal domain, such as in
alternating angles of ±10 degrees relative to the aiming
axis of the system.
Line Arrays. Modern line arrays do not consist of a
line up of individual cone loudspeakers, but instead of a
linear arrangement of wave-guides of the length l,
which produce a so-called coherent wave front. In
contrast to the traditional sound columns, these arrays
radiate in their near range so-called cylindrical waves.
This near range is frequency dependent and only valid
up to the following distances r:
(35-23)where,
array length and wavelength are in meters.
In 1992 Christian Heil was the first to present this
new design at the AES in Vienna.^17 With the product V-
DOSC by L-Acoustics, a new technology was intro-
duced which can now be found with modifications in
the product range of more than forty manufacturers
(compare Fig. 35-17).
The characteristic feature of these systems is that the
sound levels decrease in the near range by only 3 dB
with distance doubling, and begin to decrease like those
of spherical radiators only beyond the near range. This
way it is possible to cover large distances with high
sound levels and without having to use delay towers.
Digitally Controlled Line Arrays. A way of reducing
the frequency dependence of the directional characteris-
tics and beaming of sound lines consists of supplying
the sound signal with different phases and levels to the
individual loudspeakers in an array.
Duran-Audio was one of the first manufacturers that
reduced the length of its Intellivox loudspeaker lines
with increasing frequency by electronic means (so-called
DDC solution). This solution resulted in loudspeaker
lines with pronounced directivity in the vertical domain
and constant sound power concentration in the hori-
zontal domain.^18 Fig. 35-18 illustrates such a directional
effect in 3D representation.
Other manufacturers go similar ways, Renkus-Heinz
with the ICONYX loudspeaker,^19 Fig. 35-19, the French
company ATEIS (Messenger),^20 and EAW (DSA
series).^21
By changing the firmware control the following
features of such columns are possible:- Constant SPL versus distance.
- Midband frequencies.
- Noncomplex shaped audience areas.
- The performance is optimized with the following
parameters:
r l22 O= ------Figure 35-17. A Geo T series column by NEXO SA.