User manual

1.1. THE SOUND OUT FRONT! 1. Introduction
(a) (b)
(c)
Figure 1.1: Different designing approaches: (a) classic, (b) two-dimension array-ability, (c) vertical axle only array-
ability.
dimensions. Furthermore, while directivity can be shaped with a certain degree of freedom on a vertical
line, on a horizontal line the directivity features of each element can be limiting
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.
In the attempt to divulge to most people in the audio industry the operational principle of a vertical
array system, complex concepts were very often banalized so much that false notions started circulating,
and some have gone as far as stating that vertical array systems can generate cylindrical wave fronts,
with great profit in terms of sound propagation
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. Curiously enough, such inaccurate notions spread
rapidly and took root in the mind of many technicians in the field. We now need to state clearly that a
sound source of finite dimensions, such as an array, cannot generate a cylindrical wave front
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.
The operational principles of a vertical array of sound sources are basically two: for the medium-lower
end of the audio spectrum we use the interference of a set of sources that are naturally not very directive
in order to obtain a controlled directivity for the whole array; for the upper portion of the audio spectrum
we use very directive sources in order to obtain minimal interference among them when combined in
an array. At a low range a vertical array employs the phenomenon of interference in a constructive way,
using the main emission lobe which originates naturally because of the combination of sound sources.
When frequencies grow higher, though, secondary lobes appear and their energy content gets higher
and higher, therefore interference can no longer be used to obtain directivity. See the appendices at the
end of this manual for a more detailed description of the combination of sources in vertical array.
As for the higher portion of the frequency range, through the years we have seen several types of
cylindrical wave moulding devices which should allow the transformation of the emission of a driver into
a portion of a cylindr ical wave, that is if seen in section of a flat wave, and some have gone as far as
stating that in order to obtain a real line array you must employ such a device. What it should do is
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However, directivity on the horizontal axis depends on the number of elements in use.
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As we know, the emission of a single point source diminishes by 6 dB for every doubling of distance, while a cylindrical source
diminishes by 3dB.
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Meyer Sound. Line Arrays: Theory, Fact and Myth. Meyer Sound Laboratories Inc., 2002.
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