BRUEL & KJAER 4128-C - Page 31

CHAPTER 2
Characteristics
25
Fig.2.2 Typical Talker Free-field frequency Response of Type 4128-C (20Hz – 20 kHz)
Normalised Free-field Response Distribution
The sound-pressure level distribution around the mouth of Type 4128-C is shown in Fig.2.3 for
“whole speech”; it closely follows that found around the human mouth. The measurement was
made with the mouth insert in place.
Fig.2.3
The sound pressure level
distribution around the
mouth opening with the
mouth insert in place
(average from 300Hz to
3.3kHz)
20 200 2k 20k
Frequency (Hz)
40
50
60
70
80
90
dB
SPL
990062/1
050214
Vertical Plane Horizontal Plane
80
100
mm mm
60
40
20
80
100
60
40
20
0 20 40 60 mm 80 100 0 20 40 60 mm 80 100
–14
–12
–10
– 8 dB
–6
–4
–2
0
+2
+4
+6
–14
–12
–10
– 8 dB
–6
–4
–2
0
+2
+4
+6