A pressure wave occurs at the instant when a high speed train enters into a long tunnel. The wave propagates downstream to the tunnel exit and low frequency noise is radiated from the exit to outer space. The low frequency noise causes a lot of problems1 to the residents living near the exit and has a close relation with the pressure gradient of the pressure wave. To attenuate the low frequency noise, an active cancellation system rather than a passive one is developed. This research uses a model tunnel to examine the characteristic of the pressure wave and investigates the possibility to reduce the low frequency noise by reducing the pressure wave gradient with active cancellation.
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