6 Acceptable Deviation

Corrected test cases for control of Nord2000-road

To check whether a software provider has implemented the Nord2000 prediction method correctly, all the test examples in this report shall be calculated.

The overall A-weighted sound levels (L_Aeq,24h, L_AE, L_Amax) shall not deviate by more than 1 dB from the calculated results in any example specified in the present report. In most cases the deviations can be kept within 0.5 dB. Deviations exceeding 0.5 dB should therefore give rise to increased awareness concerning possible errors in the software under test, and the reasons for the deviation should be explained.

The calculated third octave band spectra shall be compared to the third octave spectra in this report. Deviations less than 1 dB are in general acceptable for the sound level values in each frequency band. Deviations exceeding 1 dB in one frequency band shall be investigated. Special problems may occur at ground effect dips in the frequency spectrum where the uncertainty may increase. A shift in the dip may lead to a considerable sound level difference in a frequency band close to the dip. A shift in the dip frequency of one third octave will in general be considered acceptable in such cases.

The length of road section actually included in the calculations will affect the calculated results, and particularly the calculated spectra may be sensitive to variations in the length. In group 1 and 4 an infinitely long road is assumed in the calculations and in group 2 and 3 a section of 40 times the shortest distance to receiver is included for practical reasons. If possible, this should be simulated in the software to be tested. Otherwise higher deviations must be expected depending on the actual length of the road section.