The variation
in
microphone sensitivity with temperature
i"s
shown for
two
typical 4145 microphones
in
Fig.5.9. The flexible extension rod should
be fitted when operation over temperatures of more than 50°C,
so
that
the
Input Stage
is
not overheated. Apart from
that,no
precautions are necessary
to
retain the fidel·ity of
the
Input Stage.
The temperature range over which
the
calibration
of
the
complete
apparatus changes by
less
than 0.5
dB
is
-20
to
+
50°C.
When the micro-
phone
is
operated
at
more extreme temperatures it
is
advisable
to
recalibrate
the
whole system.
+ 1
0
-1
I
+
20°
+
50°
-22°~-
Input
Stage +
Input
Amplifier
~
220-
+
20°
+
50°
I s I I
0
I l A
..
Input
tage
+
Input
+
utput
mpl1f1er
+ 1
iii
0
~
5:
-1
c
0
c.
IG
0::
+ 1
+
50°
~
+
20°
~
r-
-220
read
from
AC
output
~
22°
oo-
I
~
·+
20°
I
+
50°
Input
Stage +
Input
+
Output
Amplifier
read
on
2209
meter
Q)
.
~
0
"'
Qi
0::
-1
-2
-3
+
20°
.
-
+
50°
~
-220
-
-
-~
~
~
-22°
'
00
-
+
20.0
+
50°
2 5 10
20
5 k 10 k
20
k
50
k 70 k
100
k
200
k
10911
-f
Frequency (Hz)
Fig.5.10. Frequency
responses
for
various temperatures
5.6.
PRESSURE
The effect of static ambient pressure
on
the
frequency response and
sensitivity
of
the Microphone
4145
is
shown
in
Figs.5.11 and 5.12.
Fig.5.11 was measured
at
250
Hz
and should
not
be applied
at
any
other
frequency
without
reference
to
the
frequency response variations. A
58
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