Sound moves quite slowly. An echo demonstrates how slowly it moves – shout at a distant building and you can hear your voice bounce back at you with a slight delay. It moves slowly enough (330m/s) that your brain can detect a time difference between the sound arriving at your left ear and your ri...

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 w...