Don't bother even trying: It makes no sense from a physics standpoint. The electrical impulses need to be turned back into vibrations in order to move air, which is the way a speaker works. Putting the two wires on the back of a penny is a lie.
Here is Myth Busters taking this myth on (it's pretty funny):
There are some examples of homemade speakers that will work and will teach us about the necessary laws of physics that we all must follow. Here is one that makes sense:
There are others out there with variations of a theme ussing plastic cups, etc. Will they sound as good as your Yamaha's, JBL's or M-Audio monitors? I can pretty much tell you for a fact, no. But it will be a good learning experience even if it's not a good listening experience.
