Please READ MORE for the video.
Pay attention for sonic booming when train get into tunnel! After that, you can hear noise of train at the outside of the tunnel. It's about piston effect, air mass in front of the train and input and output design of the tunnels. Some tunnels' output have silencer design like nozzles.
Also some HSTs (Shinkansen 500) have special nose design like Kingfisher. Because, when we observe a kingfisher while its diving to water to hunt, we realise that, due to design its beak it doesn't splash water .
Video uploaded by trainfart
https://www.youtube.com/user/trainfart
Photo : Paul Sawer
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