Development of an Active Noise Reduction System to Improve the Residential Sound Environment around a portal of High Speed Train Tunnel

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Because of the increase of cross-sectional area of the train like double decker Shinkansen and the speed-up of it, noises are emitted from the portals of tunnels. One is MPW (Micro-Pressure Wave) and the other is LFN (Low Frequency Noise). The big MPW has a sound of "Don" like distant thump of a cannon and annoys people. LFN vibrates windows or doors of residents around the tunnel exit. They worsen residential sound environment.In this study, active noise control system for MPW and LFN was developed. The system can adapt to the various conditions, i.e., shape and speed of the train, inner structure of the tunnel and so on. In order to reduce the level of MPW or LFN, a control wave, that is positive pressure, is generated at a side-branch and is superposed on the incident wave front of a compression wave or LFN propagating through the tunnel.The active noise control with positive pressure described in this study is novel method and has higher control stability and feasibly rating compared with existing method. In addition, this technique reduces the dimension of the system as well as the cost of it.By the year of 2004, numerical analysis of this active noise control was done and the scale model experiments were carried out and both results agreed well.In the year of 2005, the practical use of this active control system for MPW was discussed and the system was applied to the reduction of LFN. To generate a control wave to superpose on LFN in a model tunnel, the software to control servo-valve was improved and the air tank capacity was increased. The generation of LFN was succeeded and it was proved that LFN can be reduced technically by the superposition of control wave which has opposite phase.