Scale modelling of railway noise barriers

Experiments were carried out in an anechoic chamber using a 1:20 scale mode l of a high-speed train to determine the insertion loss of various forms of track-side noise barrier. All the barriers investigated had the upper edge level with the bottom of the train windows and were positioned as close as possible to the train, within the limitations of the structure gauge. They thus provided attenuation of noise from sources in the lower portion of th e train, in the region of the rails and wheels. The measured performance of plane screens with rigid and sound-absorbing surfaces is compared with val ues predicted by standard prediction methods for railway noise and the resu lts of a numerical model. The effect of barrier shape and absorptive surfac es upon screening performance is investigated. Results are presented in ter ms of the insertion loss of the peak SPL of the pass-by profile for a singl e bogie noise source and for the whole train, and also insertion loss based on L-Aeq,L- 1 (h). Results for these three measures show similar trends. F or the conditions tested insertion loss values for all the screens were low er when the ground behind the barrier was absorbing than when the ground wa s rigid. The relative changes in insertion loss for the different forms of barrier were similar for the two ground types. Insertion loss values for ri gid screens were between 6 and 10 dB lower than those for similar screens w ith complete sound absorbing surfaces. The application of absorbing areas o n rigid screens significantly increases the insertion loss by between 3 and 6 dB. The least efficient screen was a corrugated barrier with a rigid sur face. The most efficient screens tested were plane and curved barriers with absorbing surfaces and a multiple edge screen with a part-absorbing surfac e. (C) 2000 Academic Press.