On the declaration of the measurement uncertainty of airborne sound insulation of noise barriers

The declaration of the results of a measurement cannot be considered complete if not accompanied by a clear and realistic declaration of the measurement uncertainty. Airborne sound insulation of noise barriers makes no exception. It is measured in the laboratory under a diffuse sound field (EN 1793-2) and in situ (EN 1793-6) in a direct sound field. The uncertainty in laboratory conditions can be assessed referring to ISO DIS 12999-1; the uncertainty in field conditions can be assessed referring to the outcomes of the QUIESST project. This paper shows how these findings should be used to derive the so called expanded uncertainty of the results, both in one-third octave bands and for the single-number ratings. An approach to presenting and interpreting the results consistent with the ISO GUM is given. The differences from the previous practice are highlighted, in particular when the classification into categories of the barrier under test for the purpose of CE marking (EN 14388) is concerned. Some ideas for the future updates of the relevant standards are proposed. For the first time, it is shown how to deal with measurement uncertainty of airborne sound insulation of noise barriers.