X212AFD
July 2021
7
Amate Audio
f= frequency (in kHz)
In the near field region
(Fresnel), the wave front is
cylindrical and waves only
expand on the horizontal plane
(100º). The height of the wave
front is, in this case, the total
height of the array.
In
the
far
field
region
(Fraunhofer), the wave front is
spherical and expands both on
the horizontal and vertical
planes.
The
horizontal
coverage is 100º 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.
Fig.6.
d
c
Calculation
A 6-cabinet array has a near field extending to 16 metres at 2kHz. Beyond this
distance the wave front will be spherical.
In the first zone (Fresnel), sound pressure loss is only 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.
