BRUEL & KJAER 4184-A, Technical Documentation Manual, Page: 10 / 52

Weatherproof Microphone Unit Type 4184-A – Supplement to Instruction Manual BE 1712 4
2.4 Calibration
The procedures for calibrating the analyzer can be found in User Manual for Hand-held Analyzer
Types 2250 and 2270 BE 1713, User Manual for Hand-held Analyzer Type 2250-L BE 1766, and in
appendix D.1 of this manual.
Weatherproof Microphone Unit Type 4184-A should be calibrated with Brüel & Kjær Pistonphone
Type 4228. Type 4228 is a class LS calibrator as specified in International Standard IEC 60942, Electro-
acoustics Sound Calibrators. The nominal frequency and sound pressure level of Type 4228 are 251.2 Hz
and 124 dB re. 20

Pa, respectively. The sound pressure level in Type 4228 is proportional to the static
pressure; therefore, the procedure in the User Manual for Pistonphone Type 4228 BE 1094 for compen-
sating for the static pressure should be followed.
The procedure for the calibration necessary for the electrical tests during conformance testing can be
found in section 3.5.
While performing the calibration procedures, the analyzer is automatically checked for its ability to
perform the measurements.
2.7 Measuring at Low Static Pressure
The frequency response of the microphone depends on the static pressure. Using a sound level calibrator
to adjust the sensitivity of a Sound Level Meter at the calibration check frequency, 251.2 Hz, provides no
information on the influence of static pressure on frequency response.
Conformance to the specified standards ensures that the system measures within the standard’s tolerances,
in the range from 85 kPa to 108 kPa. In the range of 65 kPa to 108 kPa, the change of frequency response
relative to the response at 251.2 Hz will be less than 0.8 dB.
At the calibration check frequency, the microphone is rather insensitive to variations in the static pressure.
However, Pistonphone Type 4228 is sensitive to variations in the static pressure. Therefore, the procedure
in its manual for compensating for the static pressure should be followed, see section 2.4.