Meyer Sound UltraCompact High-Power Curvilinear Array Loudspeaker M'elodie - Manual (Page 23)

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CHAPTER 5
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.
M’ELODIE CURVILINEAR ARRAY
The M’elodie loudspeaker employs a combination of drivers
to enable you to optimize both coverage and directivity in
a M’elodie line array system. To achieve optimal results, it
is important to understand how these components work
together.
High Frequencies
For high frequencies, M’elodie uses a very precise Constant
Q horn — developed using Meyer Sound’s anechoic
chamber — which provides a consistent beamwidth of
coverage in the horizontal plane.
In the horizontal pattern of an array of M’elodies, these
horns work to produce a wide 100-degree coverage; 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:
■ Wide angles: Curving a line array can aid in covering a
broader vertical area.
■ Narrow angles: Straightening a line array provides a
longer throw and coverage that 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 depends on the length of the array (number of
elements).
Directional control 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 on the directional control. The number of array
elements is very important: the more M’elodie loudspeakers
used, the more directional the vertical beamwidth becomes
at the lower frequencies. However, at low frequencies the
splay angle between cabinets has little effect since the total
length is not modified substantially.
CHAPTER 5: LINE ARRAYS AND SYSTEM INTEGRATION