When you listen to loudspeakers you hear both channels. The opposite channel is very slightly delayed and attenuated, but you still hear them. With headphones you do not. And if the producer was pan-happy, it really screws things up. There have been attempts to feed channel a over to channel b with limited success. The guy who founded HeadRoom tried it with opamps. There is a new component on Foobar2000 a designer in Germany named Jan Meier posted and there is a slider you can adjust for any or every song. Best I've seen so far. I rarely put the slider past 10. All you headphone enthusiasts should give it a try. Hell it's free.