the human ear, the results were rev

the human ear, the results were revised by the A-weighting network, in which low-frequency noises were reduced, while midand high-frequency noises were enhanced appropriately [32,33].3.2. Measured noiseAs illustrated in Fig. 11(a), the measured results were proven tobe effective by background noise of approximately 50 dB(A). Thepeak ranges of the measured noise on the open side were in agreement with those on the closed side in the time domain and theoverall SPLs were approximately 95 dB(A). The SPLs of N0 and V0in the frequency domain are displayed in Fig. 11(b). The interference of sound waves was enhanced by the multiple reflectionsbetween the noise barrier plates and the train body, resulting inhigher low-frequency noises when the train was running on theclosed side. Overall, the regularities of noise distribution wereidentical, demonstrating the equivalence between them at the relative positions.Ballast tracks have a preferable noise absorption property. Theballast is shaped like an impure medium with a great deal of frictional loss and scattering, thus reducing and perturbing the propagating noise. There are two preponderant frequencies around