As neoshinok pointed out, each park utilizes the Omni Speakers seen there. They tend to set it up in the garden beds a good distance from each other, each set at a certain volume so that way it all blends in. That way when your walking to another place, you can hear the previous music fade away as you arrive in the new land.
I actually have those Omni Speakers at my shore house here, and they work just as they would in the parks. The only problem though would be the amp, which doesn't really have that defined volume control since the thing is old. The speakers however still work as they do. I walk away from the speakers, they fade out until I get to a certain spot. Then again, Disney has multiple amps for this thing...