John Campbell and Martin Williams have investigated and written up their finding in this fantastic article about low-cost sound level meters and their claim to meet IEC61672.
It can be tempting to buy the cheapest tool for the job, especially if it claims to meet all the relevant requirements. But can these claims be trusted, should the buyer take these statements at face value or with a heavy pinch of salt?
Six low-cost sound level meters were randomly selected and tested at two independent, accredited ISO 17025 UKAS laboratories. All six meters failed at least one test, with a number failing multiple tests and basic requirements for providing the relevant information to perform a periodic test.
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In conclusion: All meters failed at least one test; some failed several tests, including linearity, frequency weighting and especially tone burst, which five of the six failed. One meter was close to passing all tests.
Each meter was advertised as being compliant with IEC 61672, which would indicate that they should meet the stringent requirements of this standard, and should pass all the tests detailed in part 3. Meters were purchased new, and immediately submitted to periodic testing per IEC61672-3, at two test laboratories. Four units failed to provide the required information in the user manual needed for a calibration check to be properly performed. In each case the manufacturer, upon request, was unable to provide the necessary information. One manufacturer did acknowledge the requirement and removed from their marketing, all claims to IEC61672.
According to the standard, testing should not normally be performed. However, for this exercise tests were made and failure of the manufacturer to provide compliance information meant that some of the tests were not accurate, as additional uncertainties were introduced. This is shown by some variance between individual calibration facilities. However, it is unlikely that the lack of this data would have resulted in failed tests becoming passes.
The results show that a low-cost meter is (as might be expected) capable of providing a noise level indication, but also that a number of instruments that claim IEC61672 compliance are not compliant. If an instrument is required for accurate noise measurements it is recommended that any claims of compliance are confirmed. This can be established by asking for evidence of type approval, typically in the form of a certificate from a national metrology institute, and not by just relying on the marketing of the sound level meter.