Amate Electroacústica,s.l.
MA210/MAW215.Version 1.11
Feb 09
6
In the near field region (Fresnel), the wavefront is cylindrical and waves only expand
on the horizontal plane (120º in
MA-210
). 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 120º 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.
Freq
(Hz)
2x
MA210
d
c
(m)
4x
MA210
d
c
(m)
8x
MA210
d
c
(m)
12x
MA210
d
c
(m)
100
Spherical Spherical Spherical
0.99
125
Spherical Spherical Spherical
1.88
250
Spherical Spherical
2 4.97
500
Spherical
1 4.56
10.48
1k
0.5 2.28 9.38
21.21
2k
1.14 4.69 18.88
42.55
4k
2.34 9.44 37.84
85.16
8k
4.72 18.9 75.71
170.4
10k
5.9 23.65 94.64
213
Fig.6.
d
c
Calculation
An 8-cabinet array has a near field extending to 19 metres at 2kHz. Beyond this
distance the wavefront will be spherical.
In the first zone (Fresnel), sound pressure loss is of 3 dB per doubling of distance,
whereas in the second zone (Fraunhofer) the loss is 6 dB. In long throw and high
SPL configurations it is very important to produce cylindrical waves .
