RCF TTL31-A, Owner'S Manual

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RCF wave guide horn
wave front interference
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6.
SOUND DESIGN
The RCF TTL33-A loudspeaker employs a unique combination of
drivers to enable you to optimise both coverage and directivity in a
TTL33-A line array system. To achieve optimal results, it’s important
to understand how these components work together.
HOW LINE ARRAYS WORK
Line arrays can provide increased gain compared to other methods of arranging loudspeaker elements. An understanding
of how specific radiating devices operate allows the creation of effective line-source arrays. In the realm of loudspeaker
systems, a line-source array is a group of similar-sized sound-radiating sources that provide increased directivity at various
frequencies. This directivity, known as the Line Array summation effect, can be predicted based on known characteristics
of the individual sources and the size and height of the array, along with center-to-center spacing of the acoustic sources.
Line arrays achieve directivity through constructive and destructive interference. The loudspeaker’s directivity varies with
frequency: When the wavelengths being reproduced are larger than the driver at low frequencies it is omni directional;
as the frequency increases (and the wavelength is comparable to the size of the driver), directivity narrows. For example,
stacking two 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. 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.
For high frequencies, TTL33-A/TTL31-A uses very precise Constant
Q horns which provide a consistent beamwidth of coverage in both
the vertical and horizontal planes. By properly aligning the acoustic
sources and observing the wavelength-related spacing, the combined
output takes on the characteristics of a coherent wave front within
the pass-band of the high frequency devices.
In the vertical pattern RCF wave guide horn-loading provides narrow
coverage in order to minimize destructive interference between adjacent
elements and 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. The horizontal directivity of a
line-source array will typically be the same as that of one of the single
elements within the array and is independent of both the number of
arrayed enclosures and the vertical configuration of the array. In the
horizontal pattern of the array, RCF wave guide horns work to produce
a wide 100-degree coverage for TTL33-A/TTL31-A. Due to the coplanar
symmetric arrangement of components, the horizontal coverage is
symmetric with respect to the 0° axis.