The Sony Walkman turns 25 this month, and if that doesn’t sound like a big deal to you, you’re probably too young to remember life without portable music. But Daniel Rubin isn’t: “For a mix-tape obsessive, this was like sprouting wings. Countless new soundtracks beckoned. I made running tapes, sunning tapes, sauntering tapes, strutting tapes. It provided groove for the quotidian, put joy in waiting. I was no longer prisoner of Donna Summer or Molly Hatchet on the radio.”