I hate to beat a dead horse, but I think rather than focusing on the strict rules of the con, we should probably just take it as a basic courtesy. There's nothing worse than having someone walk through the hallway where you're relaxing, blasting the most high-pitched, fast-paced squeaky-voiced JPop they could find.
Just as a suggestion to my fellow con-goers, don't judge your conduct based on the letter of the law at NDK. That basically presses on the staff to control everything on their own. Instead, just go by rules of thumb. If you're walking around in the halls, maybe keep your music off or at a total minimum. If on the other hand, you're sitting in a corner with your friends in between events or laps, just keep it at a 4 or 5 / 10, maybe face your player towards you, and don't cause traffic.
The NDK staff aren't outrageous or unrealistic. Don't interrupt the smooth flow of the convention, be gracious, and you'll be hard-pressed to get into trouble.