Master Audio
Xcellence Line Array Series 208.Ver 1.2 Sep 12
6
1.3. Fresnel Region (Near Field) and Fraunhofer Region (Far Field)
As our system is able to fulfil the previous conditions it will produce cylindrical waves
to a maximum frequency. The wave will be flat up to a certain distance where it will
start to become spherical (depending on the frequency and the size of the array).
The limit distance between the zone of cylindrical waves (Fresnel) and spherical
waves (Fraunhofer) can be calculated through the following formula
2
2
3
1
1
2
3
Hf
fHdc
where
d
c
= limit distance between near field and far field (in metres)
H = height of the array (in metres)
f= frequency (in kHz)
In the near field region (Fresnel), the wavefront is cylindrical and waves only expand
on the horizontal plane (110º in X-208). The height of the wavefront is, in this case,
the total height of the array.
In the far field region (Fraunhofer), the wavefront is spherical and expands both on
the horizontal and vertical planes. The horizontal coverage is 110º and the vertical
coverage is defined by the frequency and the height of the array.
Fig.5. Limits of Fresnel-Fraunhofer Regions
We can create a chart with some of the basic configurations and their performance
regarding wave propagation.
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