eli5: Why are big engines louder when idling?

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I’ve noticed that big, diesel things like locomotives and busses are really loud and shaky when idling but get noticeably quieter when they start to move. Why?

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4 Answers

Anonymous 0 Comments

Lower frequencies propagate further. Inside the motor it surely gets louder when it speeds up, but the higher frequencies are better absorbed/blocked by the material around it

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