I mean pretty much the legal effect is you can hear what's going on around you when you driving. that's the legal limits, such as emergency cars with siren on it, and people will not feel the house shake around 2 blocks away. all that crap, but I have used my subs around police cars before, they cared less unless is an emergency. also you can never never playing the music over 120 DB over 10 clock pm. which is like the sound of a jet ski, anything over 140 DB is considered Jet engine. which is should be illegal for street use. But no one really cares at all, so people like diving with subs pass 140 DB, that's why in most neighborhoods if people can hear you from over 2 blocks they can call the cops on you and giving you a disturb peace ticket. In the woofer competition people don't really care you are trying to go as loud as you possibly can. Also when cops polling you over for speeding or any other things just shot off the car, so you music wouldn't playing loud as hell on subs. Really depend on the state law and all that.
the cops have already pulled me over 3 times for subs been so loud 2 times is where I got on my drive way, so they can't do anything about it. My personal priority, another time is when I am speeding with the music so loud, the cop told me I need to turn my car off, another neighbor of my is a police officer he is pissed every time I drive into the neighbor with music so loud, so he tough me all of those things, about having subs in the neighborhood.