Operating instructions

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CHAPTER 5
High-Frequency Design Strategies
Planning for high-frequency coverage is a matter of decid-
ing the number and type of elements and fine-tuning the
splay angles between cabinets. The number of elements
does not necessarily have a significant impact on SPL at
high frequencies (it will at low frequencies), but can pro-
foundly affect vertical coverage and throw capabilities of
the array.
For the far field, a smaller mechanical splay angle between
cabinets achieves superior throw through better coupling
to compensate for energy lost over distance. The longer
the throw needed, the more elements needed with smaller
angles at the top of the array.
In the near- to mid-field, larger splay angles increase vertical
coverage. It is very important to use the correct number of
long throw devices (MILO) and short wider-throw downfill(s)
(MILO 120). The angles used between cabinets depends on
the application.
NOTE: For a smooth transition between
MILO and MILO 120 cabinets, you must use
between 13 (optimal for most applications) and 15
degrees (maximum) splay. Larger angles can create
a hole in the coverage and smaller angles can create
too much interaction.
NOTE: Due to the larger splay angle needed
between a MILO and a MILO 120, the use
of the MILO 120-I insert is highly recommended
between cabinets. The MILO 120-I insert promotes
better acoustic coupling between cabinets in the
vertical plane, as well as providing an improved ap-
pearance for the array.
Low-Frequency Design Strategies
While waveguides provide isolated control over various
mid- to high-frequency coverage areas, the low-frequency
section of a MILO/MILO 120 line array still requires mutual
coupling — with equal amplitude and phase — to achieve
better directionality.
Low-frequency directionality is less dependant on the
array’s relative splay angles and more dependent on the
number of elements of the array. At low frequencies, the
more elements in the array, the more directional the array
becomes, providing more SPL in this range. The directional
control of the array is achieved when the length of the array
is similar or larger than the wavelength of the frequencies
being reproduced by the array.
Electronically Driving the Array
Once the design (number and type of elements, vertical
splay angles and horizontal splay angles between arrays)
has been designed using MAPP online, you can effectively
optimize the array by driving it with multiple equalization
channels, or zones. Typically arrays are divided in two or
three zones depending the design and size of the array; to
optimize EQ, different strategies are used for the low and
high frequencies for long throws and short throws.
High-Frequency Equalization Strategies
For the far field, air absorption plays a critical role. The
longer the distance, the greater the attenuation at high
frequencies. In this zone, high frequencies generally need
a correction to compensate for energy lost over distance;
the correction needed is usually proportional to the distance
and high frequency air absorption.
In the near- to mid-field, the air absorption is not nearly as
critical; in this zone, high frequencies need little or no ad-
ditional correction.
TIP: If your MILO/MILO 120 line array uses a
third zone for short throws, high frequencies
in that zone may need to be attenuated to more ap-
propriate near-field levels.
Low-Frequency Equalization Strategies
Although the array can (and usually should) be zoned for
implementing different equalization curves for high frequen-
cies, similar or identical equalization should be maintained
in all the low-frequency filters. Different low-frequency
equalization settings in the same array will degrade the
desired coupling effect.
For the same reason, severe gain tapering is not recom-
mended for line arrays, since adjusting various zones with
an overall amplitude control for each results in the following:
1. Directionality decreases at low frequencies.
2. Low-frequency headroom decreases.
3. The length of the line array column is effectively short-
ened.
Figure 5.1 on the following page shows a series of MAPP
Online predictions based on an example MILO/MILO 120
system design. In this case, small vertical splay angles on
the upper part of the array for MILO are used to cover lon-
ger distances, while greater angles for MILO 120 are used in
the lower elements to increase vertical coverage for shorter
distances.