I wired an old hard drive to a LM386 audio amplifier to turn it into a speaker. I used a 9v power source and an audio jack I salvaged from an old desktop. I also added a capacitor to smoothen the sound a little bit.
Reference videos (with good explanations): for the speaker and for the amplifier, though I used an assembled LM386 board with filter capacitors and potentiometer.
The original idea / inspiration came from James Houston's remix of Radiohead's Nude.
Hard drive, second hand hard at work, basic circuit (missing extra capacitor)