BRUEL & KJAER 4111 - Page 8

5
field response of the microphone.
- ----- - - - -- - -- -- -- -
J 0 () 0 () () 0 u () () u 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 c
~ -f- - - ·-
db~ = =\ :_ .. -
- --! - - . -
_-,-
_ __: _
~
-10
'b·/
- 15 0
50
100
200
500 1000 CIS 2k
5k
10k
15k 20
'J 0
0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0
0 0 0
c
Fig. 5. Corrections to be added to the calibration curve of fig. 3 to
find the sensitivity and frequency response under
a) free field measurements, l) degree (normal) incidence with
protective grid,
b) free field measurements, 90° (grazing) inc ide nee, with
protective grid,
c) free field measurements, random incidence, with protec-
tive grid.
The frequency response of fig. 3 was valid in a free sound field with
normally impinging sound and protective grid removed.
Fig. 5, a, b
and c show three corrections which should be algebraically added to
this curve or to the corresponding curve valid for the microphone de-
livered, and placed in the back cover . in order to get the right ca-
libration curve under the following measuring procedures:
1) Free field measurements, 0 degree incidence with protective grid.
Fig. 5a indicates the diffe renee in sensitivity for the microphone with
and without grid.