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7.2. FREQUENCY RESPONSE MEASUREMENTS
The ability to regulate the output from the B.F.O. section with a feed-
back signal (compressor circuit) enables the 2010 to be used as a complete
frequency response measurement system. The B.F .0. section can be used to
excite the specimen at a constant chosen level, and the analyzer section will
then measure the response directly.
Two applications are shown below, one on vibration, and the other on
acoustics.
7.2.1. Frequency response of a microphone probe
Probe microphones can be used for a variety of applications such as
measurements in the ear, measurement of sound insulating material and at
points within intricate machinery which would normally be inaccessible.
The B & K Probe Microphone Kit UA 0040 contains probes of different
diameters and all the necessary accessories for calibration and damping of
the probes.
Fig.7.3 shows the frequency response of an undamperJ 2 mm diameter
microphone probe (24 em long). Further response measurements will show
the effectiveness of damping the probe.
Fig. 7.4 shows the measurement set-up.
BrUel
&
KJcar
BrU.I & K;c.
Bri.iel
& Kjatr
oooooooooooooooooooooooooooooooooooooooooooooooooo
Bri.iel & Kjcar
50
25
Potent iometer
Ronge:
~dB
Rectifier:
~
low.
lilft.
Freq.:
_1_0 _Hz
Wr. Speed:__!QQ__mm/se<:.
Paper
Speoed:...l.Q_mm/s•c
10
75
Copenhagen
dB dB
40
Meas.uring
Obj.:
~quency
~~
3015
S!.....!!!..i£LORhone
p~
_(without
l!2!!JRi!Jg)_20 10
- - - 1 C 5
~
~1
s;..,.
,~
oo
Qp 1124
10
20
H•
SO
100
200
Multiply Frequency Scale by
500
1000
2000
5000
10000
20000
40000 D A 8
C
l>n.
Z.•o
Lo.ol'
1612/2112
A 8
C
Un.
Fig.7.3. Frequency response of an undamped microphone probe
76
860
430
2 15
0 0
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