"Headphones", Jan Meier of Corda headphone amp fame contends, "are so unnatural that some people can't ever adapt." That's because with headphones, each ear is isolated to listen only to one channel. In real life and even over regular speakers, such isolation between the ears does not occur. Each hears what the other does. The difference is merely one of minuscule time delays and loudness attenuation (the closer ear hears the sound first and a bit louder than the ear which the head shadows). Our ear/brain mechanism uses arrival time and loudness differences between these cross-fed data to firmly allocate fixed points in space from which specific sounds arise. To get a really precise fix, humans automatically turn their heads back and forth. This adds additional difference points from altered perspectives.