What strips vocals from audio when a 1/8' audio jack is partially unplugged?
I think everyone knows that there's only one correct answer and that's phase cancellation because the dry vocal track is typically dead center in the mix.<p>Here it happens because when the earphones' ground connection is disconnected from the source, the earpiece drivers remain connected to the L and R hot signals and their former common grounding point floats and leaves them in-series.  This means that any signal present equally on L and R results in no current through the transducers.  You hear only the difference signal in both ears, although to be precise, one is actually opposite in polarity.