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Appendix
Use
of
Weighting Networks.
When using the weighting networks of the Sound Level Meter Type 2203
in
order to reduce the influence of environmental noise it should be noticed
that
a certain inaccuracy is introduced.
d
8
r-~
o-
!"""
0~
~
81~
~
0
v
n/
/'f
....
IV
0
v
ov
-1
-2
-3
-4
-5
-6
0
2
5
~
-
,...
/
A/v
102
2
~
....
~"'
5
101
2 Hz 5
I"
~
Cl+~
10'
2
16ff9#
Fig.
A.t.
Graph showing the response of the built-in weighting networks of the
Sound Level Meter.
Fig. A.1
shows
the frequency characteristics of the three weighting networks
A, B and C, and as can be seen the curves differ especially
at
low
frequencies.
A compromise has to be made in the choice of weighting curve between high
attenuation of the low frequency ambient noise and the inaccuracy of measure-
ments at low test frequencies. Normally curve "B" will suffice, and the atte-
nuations greater than 1 dB that occur at the test frequencies are listed below:
Test frequency, Hz
Attenuation, dB
200
2
250
1
315
1
4ooo
1
5ooo
1
38
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