Why is there a left and right on headphones? | BBC Science Focus Magazine

Stereo music uses interaural time difference to give the illusion that sound is coming from different directions, and headphones provide the best way to experience that illusion as they push the music directly to each ear.

But to hear stereo properly, you need the headphones on the right way round, otherwise, all the sounds will be reversed – left will come from the right and vice versa, and sounds from the front will sound like they’re coming from behind you.