If you are using your noise measurement instruments to meet any Standards, Regulations or Guidelines, it is essential that your equipment is measuring accurately. Most modern standards, regulations of guidelines will clearly state the standards to which the equipment must comply.
For example, ISO 11202:2010 states:
“The instrumentation system, including the microphones, cables, and windscreen if used, shall meet the requirements of IEC 61672-1:2002, class 1, and the filters, if relevant, shall meet the requirements of IEC 61260:1995, class 1.”
and similarly, BS 4142:2014 states:
“Select systems for measuring sound pressure levels, including microphone(s), cable(s), windscreen(s), recording devices and other accessories which conform to BS EN 61672-1, Class 1, for free-field application, as appropriate. Filters, where used, should conform to BS EN 61260, Class 1, and sound calibrators to BS EN 60942, Class 1.”
If you are going to continue to use your noise measurement instruments over a long period, it is vital that they continue to meet these same standards and this is why calibration, both Field Calibration and Periodic Verification, are an essential part of undertaking noise measurements.
Examples of why the calibration of noise measurement instruments is important include:
This is not an exhaustive list but demonstrates why it is important that noise measurement instruments are calibrated regularly and you are confident that they are measuring accurately.
A sound level meter (or any noise measurement instrument) should be calibrated otherwise it can be very difficult to show traceability when the measurements are challenged now or in the future.
If I was looking at your noise measurements, the first thing I would ask (even before looking at the measured levels) would be “Did you calibrate the equipment before and after the measurement?” and then “When were the sound level meter AND the acoustic calibrator last calibrated by a suitable calibration laboratory?”
If there’s no evidence that the equipment has been calibrated before the measurements were made and that all of the equipment had been calibrated to a suitable standard, the measurements could be called into question.