Reverse Listening Device

Yes. First thing that popped into my head, too. Although, there is one twist here. We do not process all frequencies with both ears. So, at least the volume of certain sounds would always be off. This would akin to seeing red with one eye, and blue wth the other. everything would flip upright once your brain got trained to it, but I have no idea what all happens when your freq sensors get flip-flopped like that.