These speakers clip into the headphone jack of your mp3 player, and require no external power source.
These speakers are extremely simple to build. The materials you will need are:
Two small speakers- mine were pulled from a laptop
A 1/8" audio cable
Start by stripping the wires of the audio cable, starting as close to the connector as possible. Once this is done, wire one speaker to the left channel (probably blue wire) and the ground wire, and the other speaker to the right channel (probably red) and the ground. Then you will need to cut a piece of the aluminum flashing just wider than the height of the speakers, and long enough to wrap around them. Cut a square shape out of the aluminum, where the speakers will be, and glue a piece of mesh over it. Make sure you have tabs above and below the speakers, so the top and bottom will be covered. Glue the speakers down to the aluminum, oriented so that the fronts of the speakers face through the holeand glue the audio jack next to them, so that the head is protruding well beyond the edge of the aluminum. Fold the tabs in over the backs of the speakers, and wrap the outer edges of aluminum around the back of the speakers. Glue the backs of the speakers to the inside of the folded aluminum. The overlapping bits of metal can be covered with a piece of aluminum tape.
Here it is in action: