WM-10

The WM-10 was one of the most technically ambitious early Walkman models and the one that pushed Sony's miniaturization efforts into genuinely radical territory. Released in 1983, it used a collapsible metal body that expanded for playback and contracted for storage, allowing the player to shrink to only slightly larger than the cassette itself when closed. To make that possible, Sony used a flat motor, tightly integrated internal packaging, a flexible rolled circuit board, Dolby B noise reduction, and a single-AA power system boosted through a DC-DC converter. Despite its tiny scale, it still supported multiple tape types and full playback operation.

The WM-10 mattered not only because it was smaller than what came before, but because it solved portability in a structurally different way. This is one of the clearest moments where the Walkman became a real engineering statement instead of just a consumer electronics success. It is one of the points where miniaturization itself became part of the mythology.