Has this ever happened to you? You're sitting in a noisy room with plastic water bottles, hot glue guns, and soldering irons EVERYWHERE and you can't hear your music? Fear not! You can use those conveniently placed DIY tools to make your very own really, really ghetto all-acoustic amplifier! Yes, you too can enjoy not just increased amplitude for your portable music player's wimpy headphones but also all the class of holding a plastic bottle to your ear in a public location! This really puts a new meaning to the term ghetto blaster.
Step 1: The Bottle's Labotomy
First, cut off the top of a plastic water bottle. I have no image of me doing this but think you can figure it out on your own. Then use a hot glue gun to put an old headphone you're not particularly fond of in the opening at the top. Make sure there aren't any gaps so no sound waves escape out the back. Also, be very careful not to cover the little holes in the back of the headphone with glue. If you do, it will actually decrease the volume. People who are not aware of the volume buttons on their MP3 players may want to consider this as an option.
P.S. - I am aware of possibility for a pun in the title. If you are too, please smack yourself as I am not capable of doing so.
Step 2: Splice to Mono
If you've got free time, patience, and a soldering iron, you might want to splice the headphone to mono. Ever since the invention of stereo audio in the sixties, everyone from the Beatles to your mother has thought it would be clever to have, say, a jet sound that pans from the left speaker to the right (great song, by the way. Wooh! Beatles!). Unfortunately, that causes problems when you only have a left headphone. That's where your soldering iron and years of sitting under an icy, secluded waterfall every morning come in handy. And honestly, unless you actually are a stereotypical Himalayan monk you will probably lose your patience with this step. Bear in mind that it isn't really necessary, just kind of nice for some songs. First, cut the cord of one headphone off after the point that the two converge. Then cut the main cord before they converge. Simple enough, right? You've basically just eliminated the other headphone. Then strip both cords so the actual wire is exposed. Usually there will be a copper colored wire on both sides, then on the headphone's cord there will be a red, blue, or green wire and on the input jack's cord there should be one of the same color and one of a different color. Use your soldering iron to combine the two copper colored wires and to combine the red, blue, or green wires from both sides. Congratulations, you have successfully undone the work of dozens of audio engineers.
Note: If your wires aren't standard, the two wires in the input jack's cord I call the red, blue, or green ones will be the two unique colors from both headphones. It shouldn't be too hard to figure out.
Step 3: Make an Opening in the Bottle
When you're done, the opening in the top will be sealed off, so you need some way to plug the jack into your MP3 player. Make a hole in the side of the bottle for the jack to come out of. The best way to do this is with a hot paperclip. A knife will ravage your bottle, and you don't want this work of art ruined, do you? Bend out a paperclip as shown so you have a handle, then hold the round side over an open flame until it's red hot. Then burn it. Destroy it. Pretend it's Tom Cruise announcing he's making another movie.
P.S. - There shouldn't be a black ring around the hole, I just drew that with sharpie to outline it for the photo. In fact, if yours is black, you've probably done something wrong.
Step 4: Observe the Unknown Wonders of the Universe at Work
Use your trusty glue gun to reattach the top of the bottle upside down as shown. I have no idea why, but this seems to improve the sound quality and increase amplitude a little bit. Mainly it improves the quality of the bass for projection and makes it a handy small speaker for small impromptu gatherings (like card games between classes or the weekly one-man midnight subfreezing underwear ukulele iPod-style dance contest). You can also use it for your personal listening experience to increase reverb and, if you're not very attached to your hearing, raise the max volume on your MP3 player.
Step 5: ...And You're Done!
Yay! Now you have an awesome Ghetto Blaster. There are a few other things I've been experimenting with you can try, if you want.
Use a red hot paperclip to poke holes in the bottom half of the bottle.
Put a parabolic cone on top.
Use a longer cone than the top of a water bottle.
Enjoy! And remember: one-man midnight subfreezing underwear ukulele iPod-style dance contests are awesome. Try it sometime with your new Ghetto Blaster.