PLEASE: Post your ideas to add on to this in the comments section, for everybody else, and me, to do. There's never too much music or speakers to blast while biking!
Step 1: THE INFAMOUS PARTS LIST
A cheap mp3 player, it will be alot easier if it takes a disposable battery...
A ton of duct tape
An old speaker... I used a speaker from a broken amp
Some batteries, the bigger (D) the better
A speaker cable
NOTE: You're mp3 player might break, thats why the cheaper the better...
Step 2: WHAT TO DO
Now, take your speaker and connect the stripped wire to it, and plug the other end of the cable into a computer headphone jack. Switch the wires around to the opposite sides and see which sounds better. Once you have decided the better sounding way, solder or just tape them together.
Step 3: HACKIFY ME, CAP'N!
Let's say you have something like my mp3 player. It can take a AAA, AA, C, D, two of each, anything works as long as it takes that battery. If you have a rechargeable battery, I can't really help you, but maybe you got lucky and it takes an even voltage that you can make from a few batteries. Now, take the largest battery(s) you can find, as long as they are 1.5 volts, and depending on how many batteries your mp3 player takes, hook them up in parallel, or if you have one, just tape two wires to it, one on each side. I used a C battery because I had nothing bigger. Now, either solder or tape the other ends of the wire into the corrects part of the battery holder. (Positive on the battery goes where it normally would, only with wires) Make sure they are secure...
Step 4: TAPING
Step 5: GOOD LUCK!
Like I said before, PLEASE POST IDEAS OR INSTRUCTIONS! I know there are better ideas out there, this is just a starter. Hopefully it will get people thinking about better ideas, and then those people can post their ideas here. If you make an instructable like this, post a link, or if you just have a cool idea please post it! Post some pics of my idea, or better yet your idea to give people ideas. Here is a list of other ideas that may inspire you:
better ways of mounting it
powered by the moving wheels
or better yet: