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CHAPTER 5
A line array, in the most basic sense, is a group of closely
spaced loudspeakers arrayed in a straight line, operating
with equal amplitude and in phase. Although line arrays
have been used since the 1950s, line array systems that
provide full bandwidth directivity are relatively new to the
sound reinforcement industry.
HOW LINE ARRAYS WORK
Line arrays achieve directivity through constructive
and destructive interference. For example, consider
one loudspeaker with a single 12-inch cone radiator in
an enclosure. The loudspeaker’s directivity varies with
frequency: When the wavelengths being reproduced are
larger than the driver at low frequencies it is omnidirectional;
as the frequency increases (and the wavelength is
comparable to the size of the driver), directivity narrows.
Above about 2 kHz, it becomes too beamy for most
applications, which is why practical system designs employ
crossovers and multiple elements to achieve controlled
directivity across the audio band.
Stacking two of these loudspeakers one atop the other
and driving both with the same signal results in a different
radiation pattern. At common points on-axis, there is
constructive interference, and sound pressure increases by
6 dB relative to a single unit. At other points off-axis, path
length differences produce cancellation, resulting in a lower
sound pressure level. In fact, if you drive both units with
a sine wave, there will be points where the cancellation is
complete, which can be shown in an anechoic chamber.
This is destructive interference, sometimes referred to as
combing.
A typical line array comprises a line of loudspeakers
carefully spaced so that constructive interference occurs
on-axis of the array, and destructive interference (combing)
is aimed to the sides. While combing has traditionally been
considered undesirable, line arrays use combing to positive
effect: to control the directivity.
MICA CURVILINEAR ARRAY
The MICA loudspeaker employs a unique combination
of drivers to enable you to optimize both coverage and
directivity in a MICA line array system. To achieve optimal
results, it’s important to understand how these components
work together.
High Frequencies
For high frequencies, MICA uses very precise Constant
Q horns — developed using Meyer Sound’s anechoic
chamber — which provide a consistent beamwidth of
coverage in both the vertical and horizontal planes.
In the horizontal pattern of the array, these horns work
to produce a wide 100-degree coverage for MICA; in the
vertical, however, Meyer Sound's REM technology provides
narrow coverage in order to:
■ Minimize destructive interference between adjacent
elements
■ Promote coupling to throw longer distances
As more elements are arrayed in a vertical column, they
project mid- and high-frequency energy more effectively
through coupling. The amount of energy can then be
controlled using the relative splay between the elements.
Curving a line array can aid in covering a broader vertical
area, while narrow angles provide a longer throw and
coverage which more closely matches that of the mid-low
frequencies.
Mid to Low Frequencies
For the mid to low frequencies, line arrays must be coupled
together to narrow their vertical coverage and project mid
and low energy to the far field. 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. As frequencies get lower
and wavelengths get longer, the number of cabinets has a
critical effect but the splay angle between cabinets has little
effect since the total length is not modified substantially.
The number of array elements, however, is important: the
more MICA loudspeakers used, the more directional the
vertical beamwidth becomes at the lower frequencies.
CHAPTER 5: LINE ARRAYS AND SYSTEM INTEGRATION
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