Re: sympathetic vibrations--my husband says that when a
troop of armed forces is on the march, they are ordered to
march out of step going over a bridge, because the sympathetic vibrations can cause some bridges to collapse.
Also--in one of Clive Cussler's works of fiction (can't remember which, but can LIU if anyone's really interested),
the enemy had developed a weapon of incredibly destructive power that used sound waves. Bad literature, but theoretically "sound" technology, I think. [groaning at her
own unintended pun emoticon]