Frequency
Curve
A Curve B Curve C
T
olerance
Limits (d
B)
CurveD
To
lerance
Limi
ts
(dB)
Hz
dB dB dB
for Curves A, B and C
dB
for
CurveD
10 - 70.4
-38.2
-14
.3
-26
.5
3.5
12.5
-63.4
- 33.2
-11.2
3.0
-2
4
.5
3.5
16 - 56.7
- 28.5 - 8.5
3.0
-22.5
3.5
20
-50.5
-24
.2
- 6.2 3.0
-3.0
-2
0.5
3.5
- 3.5
25
-44
.7
-20.4
- 4.4 2.0
-2.0
-18.5
2.5
-2.5
31
.5
-39.4
-17.
1
-
3.0
1.5
-1.5
- 16.5 2.0
-2.
0
40
-34.6
-14
.2
- 2.0 1.5
-1.5
-14.5
2.0
-2
.0
50
-30.2
-11.6
-
1.3 1.5
-1.5
-12
.5
2.0
-2.
0
63
-26.2
- 9.3 - 0.8
1.5
-1.5
-11
2.0
-2.
0
80
-22
.5
- 7.4 - 0.5 1
.5
-1.5
- 9 2.0
-2
.0
100
-19.1
- 5.6
-
0
.3
1.0
-1.0
- 7.5
1.5
-1.5
125
-16
.1
- 4.2 -
0.2 1
.0
-1.0
- 6.0 1.5 - 1.5
160
-13.4
- 3.0 - 0.1
1.0 - 1.0
- 4.5 1.5
-1.
5
200
-10.9
- 2.0 0
1.0 - 1.0
- 3.0
1.5
- 1
.5
250
- 8.6
-
1.3
0
1.0 - 1.0
- 2.0
1.5 - 1.5
315
- 6.6 - 0.8
1.0
-1
.0
-
1.0 1.5
- 1.5
400 - 4.8
-
0.5
1.0
-1.0
- 0.5 1.5
-1
.5
500 - 3.2 - 0.3 1.0
-1
.0
0
1.5
- 1.5
630
-
1.9 - 0.1 1.0
-1.0
1.5
- 1
.5
800
- 0.8
0
1
.0
- 1.0 1.5
-1.5
1000 0
1.0
-1.0
1
.5
-1.5
1250 0.6 1.0
- 1.0 2.0
1.5
-1.5
1600
1.0
- 0.1 1
.0
- 1.0 5.5
1.5 - 1.5
2000 1.2 - 0.1 - 0.2 1.0
- 1.0 8.0
1.5
-1.5
2500 1.3 - 0.2 - 0.3 1
.0
- 1.0 10 1.5
-1.5
3150 1.2
-
0.4 - 0.5
1.0
- 1.0
11
1.5
- 1.5
4000
1.0
- 0.7
- 0
.8
1.0
- 1.0
11
1.5
-1.5
5000
0.5
-
1.2
-
1.3 1
.5
-1.5
10
2.0
-2.
0
6300
-
0.1
-
1.9
-
2.0
1
.5
-2.0
8.5 2.0
-2.
5
8000
-
1.1
- 2.9
-
3.0
1
.5
-3.0
6.0
2.0
-3
.5
10000
- 2.5 - 4.3
- 4.4
2.0
-4.0
3.0 2.5
- 4.5
12500 - 4.3
- 6.1 - 6.2
3.0
-6
.0 3.5
- 6.5
1
6000
- 6.6
- 8.4 - 8.5
3.0
- 4.0 3.5
20000
- 9.3
-11.1
-1
1.2
3.0
- 7.5
3.5
Table 4.1. Tolerances on the performance
of
the
Weighting Networks
of
a
Precision
Sound Level Meter
as
a whole, in a free sound field
with incidence normal to the microphone diaphragm
4.7. ATTENUATOR
II
AND
OUTPUT AMPLIFIER
To
obtain the best possible
signal
to
noise
ratio the output attenuator
is
divided into two sections, both operated by the
same
knob. The first section
comes
immediately after the weighting networks
and
the
second
after the
output
amplifier.
The
attenuator
has
a
range
of
0
to
50
dB
and
is
divided
into
10
dB
steps.
Its frequency characteristics are shown in Fig.4.11.
The output
amplifier
is
divided into three sections. The first
is
placed
between the two attenuator sections. The
second
acts
as
the driver for the
high
voltage output section, from which the detector circuit
is
driven.
The
output from this section
is
lead
to
an
external socket from which
an
AC
35
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