...under headphones you will hear your left speaker in your left ear and your right speaker in your right ear. All good? Well let me tell you that is not "natural" or rather is not how any living thing has perceived sound over the last millions of years. With speakers, you will hear both your left and right speakers in both your left and right ear, but in different volume and differently timed/delayed. This is called crossfeed, the left side feeds into your right side and vice versa.