scope:

This European Standard describes a test method for determiningthe intrinsic characteristics of sound diffraction of added devicesinstalled on the top of traffic noise reducing devices. The testmethod prescribes measurements of the sound pressure level atseveral reference points near the top edge of a noise reducingdevice with and without the added device installed on its top. Theeffectiveness of the added device is calculated as the differencebetween the measured values with and without the added devices,correcting for any change in height (the method described gives theacoustic benefit over a simple barrier of the same height; however,in practice the added device can raise the height and this couldprovide additional screening depending on the source and receiverpositions). The test method is intended for the followingapplications: preliminary qualification, outdoors or indoors, ofadded devices to be installed on noise reducing devices;determination of sound diffraction index difference of addeddevices in actual use; comparison of design specifications withactual performance data after the completion of the constructionwork; verification of the long term performance of added devices(with a repeated application of the method); interactive designprocess of new products, including the formulation of installationmanuals. The test method can be applied both in situ and on samplespurposely built to be tested using the method described here.Results are expressed as a function of frequency, in one-thirdoctave bands between 100 Hz and 5 kHz. If it is not possible to getvalid measurements results over the whole frequency rangeindicated, the results shall be given in the restricted frequencyrange and the reasons of the restriction(s) shall be clearlyreported. A single-number rating is calculated from frequency data.For indoors measurements see Annex A.