I have hunted around and no-one has posted this yet as far as I can tell.

I was playing with those "Sound Quietner Headphones" used for plane travel today (on the plane too...) and thought that this would be cool.

We already have the microphone input on the unit, and we put out a negative image of that to counteract the sound waves coming in the car.

This would abviously put out a negative sound image but calculate the sound that should actually come out of the car, that way we would not sit in silence

This can also spread to other ideas too, like the signal delay I have seen posted here recently, you could just use a good quality mic in the position that you want to hear the sound focused, and then the software can do the rest (Just like my PXA-600!)

Just some thoughts, that would make the sound output amazing if it could cancel the road noise we hear whilst driving.

DAMN that is a funky idea. Shame I don't know my programming