co
6
~
Without
Series
Ca~acitor
I
5l
4
c
0
sr
2
Cll
0:
Cll
>
0
-~
~
0:
-2
-4
-6
-8
-10
-12
-14
-16
-18
-20
1/2 inch Microphone
1 inch Microphone
\
Direct \ " - - -
...
~//,
\
,.
-
\.
,-r-f'-
- - -
-
-
-
............
"-
-
,L.
-
-----::...
-
~
....
-:'
/
L,
~
~
"
/
/
lP7
~~-EC
179 Requirement
/
/
A
v
I
I
/21-
With
Series
Ca~ac
i
tor
I
I'
1 inch Microphone
~/
/1-
~
1-
Direct
-1/2
inch Microphone
l/11
v
I
I
'I
I
'(
-22
2
5
10 20
50
100
Frequency (Hz)
/70-f.f?
Fig.4.9. Low Frequency Response
of
2209 with and without the series
capacitor
4.5. WEIGHTING NETWORKS
The
A,
B,
C and D weighting networks are placed between
the
input and
output
amplifiers and a graph
of
their
characteristics
is
'shown
in
Fig.4.10.
The
A, B and C
networks
comply with
the
basic shape and tolerances set
by
I
EC
Recommendation 179 and
the
proposed D
network
has been also
designed
to
lie
within these same tolerances. (Table 4.1).
These
tolerances apply
to
the
whole
meter
in a free sound field
for
normal incidence
of
the
sound waves.
The
calibration
is
only
valid when
the
operator
has a negligble influehce
on
the
sound field
at
the
position
of
the
microphone.
33
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