Optimization of in situ noise barrier intrinsic characteristics measurements

Noise barriers intrinsic characteristics evaluation is fairly complicated if one aims at simulating barrier operating conditions. One of the most successful methods consists of in situ impulse response measurement, in particular by means of MLS signals combined with cross-correlation techniques. This has been adopted by a new CEN Technical Specification. Anyway, such a method has shown limitations and drawbacks. The aim of the research is first of all to investigate the influence of various parameters, such as source characteristics, measurement apparatus geometry and signal processing technique, on the final results of the measurements. Correlation has been found between errors due to subtraction technique, used to isolate the reflected component, and differences observed in subsequent measures. Particular attention is also paid to barrier materials and shape; reflection coefficient measurements on low- as well as on high-absorptive barriers were performed. Finally, method repeatability and reproducibility were taken into account.