In 1979, Sony introduced the Walkman and changed our relationship to music. The obvious magic of the Walkman — and later MP3 players like the iPod — is that it made it easy to carry your music with you, providing a portable soundtrack for your life. But I think there was another, less obvious, transformation in music-listening spurred by the Walkman and its digital descendants: Suddenly, we all spent a lot more time listening to music through headphones. Sure, most people had a set of those big 70s corded cans sitting by the family stereo. And my dad had an earphone (singular) for his transistor radio to listen to the ballgame. But portable music players — tape, CD, or MP3 — are designed to be used with stereo headphones. And as a result, the listening experience is more immersive, more active, and almost universally delivers newfound appreciation for what you are hearing.