I don't understand your logic, Gill, as that would imply that once one person had burst the bubble, no-one else would hear the sound, surely? I'm not even sure that sound can be considered three-dimensional. Essentially every track on a 5.1 soundtrack is a one dimensional sound from a specific position. The brain re-assembles the various channels to create the 3D effect, just as the brain interprets the two monocular 'signals' from the eyes to produce three-dimensional vision.