Abstract
When a high speed train enter a tunnel, Low Frequency Noise problems occur around a tunnel entrance. This study measures low frequency noise at measurement points, which set up on meshed around a tunnel entrance, with an experimental set up at a laboratory. A sound pressure increases as the train gets closer to the tunnel entrance and decreases immediately after the entrance. Sound propagating velocity before the entrance is the same as the train speed. On the other hand, the sound propagates at the speed of sound after the entrance. Instant distribution diagrams of the sound pressure around the entrance show changes of the distribution visually when a train enters a tunnel.
