The Determination of Sound Power with ISO3744 Method in Quasi-Anechoic Environments: Problems in the Characterization of the Measurement Environment with the Comparison Method

The ISO 3744 and 3746 standards, used very often for the determination of the sound power of generic machines, require the qualification of the measuring environment. In the industrial field, the presence of environments specially designed for laboratory activities is very frequent, although they are not true anechoic or semi-anechoic chambers but they are rooms with high sound absorption, conceived as a good compromise between cost and performance . These environments are characterized by a high sound absorption, and therefore poorly suited for the characterization of the environmental corrective factor with the reverberation method. In these cases it is advisable to use the comparison method, which uses a reference source that complies with ISO 6926. However, this methodology is problematic because unjustified deviations between the sound power measured according to ISO 6926 and the sound power measured in the test environment can occur: such deviations can greatly increase the environmental correction factor and make the measurement unreliable, increasing notably the uncertainty of the result. In the present paper, this problem has been analyzed, which derives from a normative deficiency, and we want to propose a method to make the final result of the test more reliable, reducing measurement uncertainty as much as possible.