I thought I would just leave it at that, but in the interest of good karma and science:
A speaker (and just about every other electronic) needs a positive and a negative to make use of electricity; The wire's sheilding may be the negative conductor.
They don't just work on positive current, it needs a path back to the source via a seperate conductor.
And no, you shouldn't wrap the red and black around that same wire.
In fact, I would suggest you don't wire anything to anything, flip any switches, use any toasters, or put batteries in anything at all until you understand why that won't work.
In fact, I would suggest you don't wire anything to anything, flip any switches, use any toasters, or put batteries in anything at all until you understand why that won't work.