There is an old saying, perhaps you've heard it: "Your right to swing your arms around ends at the end of your neighbor's nose."
At any campground, county, state, federal, private, doesn't matter; at any campground your music is too loud if your neighbor complains. Period. End of story.
For what it is worth, given your preference for Yanni, maybe the guy next door prefers Def Leopard or Kiss. That is his right. He does not, however, have the right to play either loud enough to interfere with your enjoyment of Yanni, nor do you in reverse.
I like the suggestion of the others to acquire a set of headphones or boondock.
