There are also distance sensors for Arduino/Pi that would work too. It could actually detect your movement and allow you to bring the room you are moving to up naturally.
The way I'm thinking about this is a ride/thing at Disney where you might walk but the audio just follows you as you move around.
What would really kick ass is to eventually have this working super smooth and then get those directional, pinpoint speakers. With multiple sets of speakers in a room it would allow multiple people to jam the fuck out and not even hear the others music.