Norsonic nor118, Instruction Manual

Page: 75 / 116

62 Chapter 11
About sound power measurements
63 Norsonic Nor118
User Guide
If condition
a
exists, additional microphone positions
shall be used. For the microphone array on the parallel-
epiped, the number of microphones are increased as shown
on the next page by increasing the number of equally sized
rectangular partial areas.
If conditions
b
or
c
exist, additional measurement
positions on the measurement surface in the region of
high noise radiation shall be used. Details on this are
given in the  .
Reducing the number of positions
e number of microphones positions can be reduced
if preliminary investigations for a particular family of
machines show that by using the reduced number of
microphone positions, the determined surface sound
pressure levels do not deviate more than 1 dB from those
determined from measurements over the complete set of
microphone positions in accordance with the procedures
described above.
An example is when the radiation pattern is shown to
be symmetrical.
e overhead position(s) may be omitted for safety
reasons, if so stated in the relevant noise test code.
Mic. positions – one reflecting plane
Each plane of the measurement surface shall be considered
on its own and so subdivided that the result is the smallest
possible number of equal sized rectangular partial areas
with a maximum length of side equal to 3d (see the Fig.
to the right). e microphone positions are in the centre
of each partial area. In this way the other positions shown
overleaf are obtained.
More than one reflecting plane
For a source installed adjacent to more than one reflect-
ing plane, reference shall be made to the figures shown
on this page spread for the purpose of defining a suitable
measurement surface. Microphone positions are as shown
in the Figs).
Procedure for fixing the specified microphone positions
where a side of the measurement surface exceeds 3d
≤
3d
≤
3d
≤
3d
≤
3d
≤
3d
≤
3d
≤
3d