Technically, in an apartment, your property line is the wall of your unit, so if your neighbor can hear it at all after 11, it's a violation. The trick is, when the cops show up, they have to hear it too. You can't get a ticket for hearsay.
I know this 'cause I got warning ticket once in college when the neighbors cranked up their stereo super loud. The other neighbors call the cops. When the cops came, the loud neighbors had already turned off the music and left, but I happened to be playing music with the sliding glass door open. Since the cops could hear it, I was given the warning. What was dumb was that it was like 3pm in the afternoon.
But the cops were actually pretty cool and ended up checking this new fangled thing called "mp3" that let me play music on my PC piped out to my stereo (it was like 1996 after all).
