ABSTRACT
Accuracy-Calibration Sound level meters are delicate items of equipment and must be calibrated by means of an acoustic calibration device at regular intervals, preferably before and after each time they are used. Reliance upon an internal calibration facility in the sound level meter itself is not satisfactory, as this does not check the most vulnerable part of the system, i.e. the microphone. Unfortunately, even acoustic calibrators are not 100% reliable and it is good practice to carry out a calibration using both the calibrator and the internal calibration signal. These should cross-check. If they do, the calibration can be relied upon with reasonable confidence since the probability of identical errors in both systems is extremely remote. If the two calibrators do not correspond, the reasons for the discrepancy must be investigated.
