BRUEL & KJAER 4188 - The Calibration Chart

Chapter 5 — Free-field
1
/
2
" Microphone Type 4191
Introduction
Falcon™ Range of Microphone Products
Microphone Handbook
BE1377– 12
5
−
3
5.1.2 The Calibration Chart
Each microphone is supplied with an individual calibration chart (see Fig.5.2)
which gives the microphone’s open-circuit sensitivity, polarized capacitance and
free-field and actuator frequency responses.
Open-circuit Sensitivity
The stated open-circuit sensitivity is valid at the reference frequency (251.2Hz
*
) for
free-field, random-incidence and pressure-field conditions. The stated uncertainty is
the U
95
value (the value valid for 95% confidence level).
Ambient Conditions
The ambient conditions are measured continuously during calibration at the factory.
The calibration results obtained at the measured Environmental Calibration Condi-
tions are corrected to the reference ambient conditions stated under Valid At (23°C,
101.325kPa and 50%RH).
Frequency Responses
Two frequency responses are shown on the calibration chart. Both are normalized
to 0dB at the reference frequency (251.2Hz
*
).
The upper curve on the calibration chart is the individual microphone’s open-circuit
0°-incidence free-field response. This response is the optimized response for Free-
field
1
/
2
" Microphone Type 4191.
*The exact reference frequency is 10
2.4
Hz (re ISO 266).
Fig.5.2 Microphone calibration chart
Frequency Hz
dB
+ 5
0
– 5
– 10
– 15
1 2 5 10 20 50 100 200 500 1 k 2 k 5 k 10 k
– 20
20 k 40 k
+ 1
– 1
940952e
Dotted Curve Shows Typical Response Free-field Response 0° Sound Incidence
Actuator Response
0° Sound Incidence
See the microphone handbook for further information
BC 0226 – 12
Bruel & Kjær
B
K
7/6-'89

Free-field 1/2" Microphone
Type 4191

Calibration Chart

Serial No:
419111A 

Open-circuit Sensitivity*, S
0
: -37.9 dB re 1V/Pa 

Equivalent to: 12.7 mV/Pa

Uncertainty, 95 % confidence level 0.2 dB 

Capacitance:
18.2 pF 

Valid At: 
Temperature:
23 °C
Ambient Static Pressure: 101.3
kPa
Relative Humidity: 50 %
Frequency: 250
Hz 
Polarization Voltage, external: 200 V

Sensitivity Traceable To: 
DPLA: Danish Primary Laboratory of Acoustics 
NIST:
National Institute of Standards and Technology, USA 

IEC 1094-4: Type WS 2 F



Environmental Calibration Conditions:

100.1 kPa 25 °C 35 % RH

Procedure: 704217 Date: 21. Apr. 1994 Signature:


*K
0
= – 26 – S
0
Example: K
0
= – 26 – (– 38) = + 12 dB
