It is reported that not only an audible noise but also a low-frequency noise including an infrasound is radiated from a high-speed train (called Shinkansen in Japan) toward a wayside open area. Although these noises become larger as the train speed increases, the cause of the low-frequency noise remains to be fully clarified. In this study, we investigated the wayside low-frequency noise at two sites : a viaduct section and an embankment section. The investigation results show that the observed low-frequency noise consists of two phenomena, the one is a train passing pressure variation around the nose and tail parts of the train, the other is a low-frequency acoustic pressure wave caused not only by an aerodynamic source around the train but also by a viaduct vibration. The maximum sound pressure level of the low-frequency noise is determined by these phenomena which have different magnitude depending on the train speed, a measurement distance and a type of running section. Furthermore, the characteristic of the measured low-frequency noise in a high-speed region, which is analogous to a line source, shows that the low-frequency noise is mainly related to the aerodynamic sound emitted from all over the train.
