Elbow is a clever, perhaps too clever, cassette player concept that was unveiled by the "audiovisual art organization" BrainMonk a year ago. Now BrainMonk is looking into the feasibility of actually building it, and has put out a PDF that details the necessary components, according to Music Crowns.
The concept itself is simple: what if a cassette player didn't have any of that nasty boxy stuff that protects the cassette? Elbow, were it to exist, uses a single pulley to drive the tape, and it tracks the tape with an optical sensor to keep a constant playback speed — a serious problem with cheap cassette players.
Elbow's biaxial arm can swing up to accept a tape, and switch sides to change playback direction. (If you'll recall, cassette tapes need to be "flipped" to hear both "sides" of a recording, while fancier cassette players can just play them in reverse.)
I'm curious what kind of battery life you could get out of an object like this. My guess is not much. But, really, this concept is more of a fashion accessory than a 21st century sequel to the Walkman — just like the cassette tapes that it will theoretically play.