Drastically different. Headphones use your ears, or a closed design. Plug in a set of headphones, then pull them off your head 2 inches....Also do you drive with your head against the head rest?Most people dont. Its been done, and again, its usually not well received. As said, you could do some sugnal processing to delay the high frequencies a bit so they all arrive to the ears at the same time, or close, but that will change depending on the volume...the louder you go, the more out of wack it will be....Now if you listen to talk radio then it wont matter....use them. I prefer a bit of distance between me and the speakers to create the proper staging....but again thats just me.