OK, I'm curious. Why would the negative be an output. Negative should be an input from whatever electrical user, for a path back to ground, no?
The speaker doesn't just push out, it pulls in too. The audio signal is alternating current. For parts of the signal which are above 0, the P output device is active, for parts of the signal below 0, the N output device is active.
Actually, the P device is run slightly into the negative (even though it is very inefficient to do so), and the opposite for the N. This minimizes zero-cross distortion.
