Cirrus Research CR:811C User Manual

CR:800C Series Sound Level Meter User Manual
Page 67
10.5 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 Cirrus
Research plc.
Calibration corrections are listed below for the Cirrus Research plc ½" 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.

Cirrus Research CR:811C Specifications

General

Brand	Cirrus Research
Model	CR:811C
Category	Measuring Instruments
Language	English