BRUEL & KJAER 4188 - Page 171

Chapter 7 — Low-frequency Pressure-field
1
/
2
" Microphone Type 4193
Sensitivity
Falcon™ Range of Microphone Products
Microphone Handbook
Brüel & Kjær
7
−
6
data disk (see section 7.1.3). The nominal sensitivity for a microphone without
Adaptor UC0211 fitted is shown in Table 7.2.
7.2.2 Loaded Sensitivity
When loaded by a preamplifier, the sensitivity of the microphone is given by:
(7.1)
where S
C
= overall sensitivity of microphone and preamplifier combination
S
O
= open-circuit sensitivity of microphone
G = voltage gain of microphone and preamplifier combination (in dB)
With Microphone Preamplifier Type 2639: G = –0.1dB
With
1
/
2
" Microphone Preamplifier Type 2669: G = –0.2dB
With
1
/
2
" Microphone Preamplifier Type 2669 and Adaptor UC0211: G = –16.5dB
(
±
1dB)
Example
Loaded sensitivity of typical microphone with
1
/
2
" Microphone Preamplifier Type
2669:
S
C
= –38.3 + (–0.2) = –38.5dB
Loaded sensitivity of typical microphone with
1
/
2
" Microphone Preamplifier Type
2669 and Adaptor UC0211:
S
C
= –38.3 + (–16.5) = –54.8dB
7.2.3 K-factor
Some types of Brüel&Kjær instruments use the K-factor (correction factor) or the
K
O
-factor (open-circuit correction factor) for calibration.
(7.2)
(7.3)
Nominal open-circuit sensitivity Accepted Deviation
(dB)
mV/Pa dB re 1 V/Pa
12.5 – 38
±
1.5
Table 7.2 Nominal open-circuit sensitivity
S
C
S
O
G
+=
K
26
–
S
C
–=
K
O
26
–
S
O
–=