Model 90 Quantifier Sound Level Meter
Page 66
Free Field Correction
When calibrating a microphone which is to be used for free field measurements, a small
correction may be necessary to compensate for the difference between the
microphone's free field response at 'zero degrees' or 'head-on' incidence and the
pressure level generated by the calibrator.
The correction is typically -0.3dB for ½ inch microphones (making the effective
calibration level 93.7dB).
The table below shows the correction values for the standard microphones of Pulsar
Instruments Plc.
Calibration corrections are listed below for the Pulsar Instruments Plc½" Capsules and
three microphone capsules commonly used in Calibration Laboratories:
Microphone Correction Values
Microphone Type
Calibration Correction Effective Calibration Level
MK:202
-0.3dB
93.7 dB
MK:215
-0.3dB
93.7 dB
MK:216
-0.3dB
93.7 dB
MK:226
-0.3dB
93.7 dB
MK:224
-0.3dB
93.7 dB
B&K 4134
0dB
94.0 dB
B&K 4180
0dB
94.0 dB
B&K 4192
0dB
94.0 dB
Example
An example of the procedure used to calculate the value for an MK:224 microphone is
shown below :
Level = 94.0dB + Microphone Correction
Level = 94.0dB + ( -0.3dB)
Level = 93.7dB
Different microphones will have different correction values. Please check the operation
manual for the Sound Level Meter or microphone concerned for details.
