It was designed to be a as small as possible(so I could use it in school, shh...), and it's fairly simple.
-PVC pipe that roughly matches the size of the speaker
-a pair of headphones that you are willing to destroy
-more super glue
Sorry, I already made it, but you can still see inside of it.
Step 1: Cut Headphones and Solder
Cut around 5 inches from the end of the cord. Strip an inch off and you'll notice 3 wires inside. Usually two are insulated. Just twist those two together, making the positive wire. The other one will be negative. Burn or melt(with soldering iron) the insulation off of the positive(the two you twisted). Then plug in your music player and touch it to the speaker thingyz to make sure it works before you solder. If it works you can solder 'em up, but make sure you grab the handle. Unfortunately, I missed.
Step 2: Cut PVC
I am going to warn you, shit gets EVERYWHERE when you cut PVC. I used the Dremel and cut it a bit longer than the speaker, then I sanded it and smoothed it out. I used the "male PVC" so the bottom was nice and curved since I cut the part with the threads off. This is the case.
Step 3: Make a Lil' Hole
Now it's time to drill the hole that the cord goes through. It needs to be big enough for the jack to fit through. Because of my shitty soldering, I wrapped the cord around the back of the speaker and super glued it down, in case someone wants to yank the cord and whatnot. Now, I don't have huge drill bits either so I just drilled a hole and then used the sander bit and smashed it through.