Two thoughts here.
1. Being loud is not necessarily a good thing. If I can hear you from across the park, why should I walk over near you to drop money in your case? I once saw a trumpet player on the wall by the Mississippi river in New Orleans, playing with a mute. I could tell he was good, but I could barely hear him. Got my cafe au lait to go an walked over near him to listen. Gee, what a suprise, when he was finished, there was a nice little crowd surrounding him when he made his polite pitch for donations. He cleaned up.
2. Walking from O'Hare Airport to the Elevated station, heard great electric blues. The busker was sitting right in a bottlenecked portion of the hallway, you had to pass him. I got to hear him (over all the ambient noise) for a pretty good distance, even though I didn't have time to stop. He was good, and I kicked in.
I guess the point is you got to think about it, and be appropriate.
Blues