Acoustic intrinsic performances of noise barriers: Accuracy of in situ measurement techniques

Laboratory and in situ methods have been used for measuring intrinsic performances of noise barriers, as prescribed by the European standard series EN 1793. The use of in situ techniques is promising, but their accuracy has to be duly verified, even in comparison with well-known standardized procedures. Sound insulation and reflection properties have been measured through a MLS-based technique in an outdoor test field. The paper analyzes the procedures that mainly influence the accuracy: correction for wave spreading and time windowing. Repeatability of the in situ method for sound insulation is satisfying and its results look consistent with simple prediction models. Nevertheless, in situ data can be overestimated at low frequencies, due to the overlapping of the transmitted and diffracted components. The method has to be carefully employed when the sample shows apertures as slits or holes, unless a different kind of sound propagation is assumed at the receiving side. A good agreement was found between in situ and laboratory sound insulation data, while in situ and laboratory absorption properties show poorer correlation.