X-Treme Audio MISI - Manual (Page 9)

LINE ARRAYS
10. MISI TM system: from “AS IS” to “TO BE”
The MISI TM ( Middle-Sized line array) vertical line array can be de-
fined as a suitable compromise between power, weight and size.
The designers of the
MISI TM system aimed to create a series of line
array speakers capable of achieving considerable sound coverage
with reduced bulk and weight. As a result, the system is particularly
suitable for both middle-large tours as well as indoor and outdoor
fixed installations.
The
MISI TM system provides the right solution to the needs of those
working in the live sector and/or dealing with sound reinforcement
of large spaces. Each loudspeaker system offers 120° coverage
horizon tally and 15° coverage vertically. The trapezoidal enclosure
corners of the
XTMISI unit have been designed so that a 2 x 7.5° an-
gle is achieved when two loudspeaker systems are set side by side.
Thanks to the suspension mechanics, starting from an array made of
side-by-side
XTMISI modules (7.5° x 2 = 15° between the different
cabinets), the various cabinets can be progressively “opened” by us-
ing the rear bars and selecting the hole ensuring correct positioning, in
order to obtain arrays with different curvatures (fig. 12). The mechanical
suspension system designed for the vertical line array module
XTMISI
allows the angle between two speakers to be adjusted, with a 1° reso-
lution, from 0° to 15°, corresponding to two side-by-side loudspeaker
systems and a line array respectively.
fig. 12
Therefore, each element generates a linear wave-front with a con-
stant phase and allows overall assembling of several elements pro-
ducing a single and broad sound source. Since the separation angle
between the elements is adjustable, the wave front can be modelled
by varying the shape of the array.
As regards the interferences occurring in all audio systems, the
XTMISI line array module has been designed to obtain a construc-
tive interference in the declared coverage area and destructive out-
side this area. Moreover, thanks to successful coupling right across
the audible spectrum, the
XTMISI element generates a coherent
wave-front on a large area with tiny variations in frequency response
and sound pressure level. Therefore,
MISI TM is a broadband audio
system, which remains coherent up to very high frequencies.
On a horizontal plane, the whole line array, made of different XTMI-
SI modules, shows the same directivity as a single element (120°).
On a vertical plane, coverage is determined by the number of array
elements and by a specific separation angle between them. Given
this predictability, vertical coverage can be optimized in order to be
adjusted to the specific geometry of the area to be covered.
The high SPL attenuation levels outside the coverage area make the
MISI
TM system an excellent solution for all situations in which envi-
ronmental noise should be avoided, such as, for example, in open
air amphitheatres located near residentia l areas.
The accuracy, flexibility and predictability of the X-Treme approach
to sound reinforcement open up new horizons for sound design.
11. Types of installations
In practice, not all the line arrays permit a straight-line configura-
tion. In fact, depending on the application and any specific needs,
the array can be curved in order to obtain sufficient coverage for
the entire listening area. For this reason, every loudspeaker system
making up the line array can include a flying system by which it can
be hooked and then oriented on a vertical plane. It should be noted
that the flying system, being an integral part of the speakers, has
been conceived so that the front hooking can ensure correct spac-
ing out between the different units (while the rear hooking modifies
the vertical orien tation consistently with theories on line arrays).
Thus
J-shaped systems are quite common although, of course,
there are some constraints for their theoretical application such as
a limit for the maximum opening angle that can be achieved. One of
these conditions is specified below: in curved arrays, the opening
angle is inversely proportional to the distance of the listening point -
to be more precise, in the farthest positions the angles must be very
small and they should become progres sively larger as the listening
point gets nearer to the line array. The vertical coverage of a curved
array is given by the dimension and height of each loudspeaker sys-
tem, by the opening angle between the various cabinets and by the
number of flying modules.
Ground stacked or flying?
Although
flying systems are generally preferred by most sound
technicians, there are a lot of arguments supporting both solutions.
In many cases, however, the best solution depends on the logistical
characteristics of the space to be sound reinforced or, simply, the
system cannot be suspended at all.
The perception of the sound image from the stage provided by the
stacked systems is a positive element when small areas have to
be sound reinforced. The stacking systems offer a higher SPL at low
frequencies thanks to the coupling with the floor. In addition to these
geometrical reasons, a stacked array can achieve a larger vertical
coverage as compared with a flying one. For all these reasons, the
stacking systems are more useful in small configurations where just
a few elements are sufficient to achieve an excellent coverage of the
audience.
On the other hand,
flying systems are the best solution to achieve
a uniform sound pressure level if the total ratio between the number
of flying elements and the area to be covered is sufficient to guaran-
tee a suitable coverage from the front to the back. Flying systems
also provide an excellent solution for the quite common sightline
problems and allow high frequencies to better penetrate into listen-
ing area with a reduced shadow effect. As for flying configurations,
some additional loudspeaker systems are required to cover the
central area of the first rows (“front-fill”) which enable the localiza-
tion of the sound image on the stage for the first 10-20 rows of the
audience.
Side-by-side
speaker systems (15°)
Array curvature
adjustment system
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