This subject has many arguments over weather this has any real evidence! Some would argue that its in your head and the differences are made up! Some would argue that your ability to hear the different sound frequencies have adjusted to your own personal sound setup over time so you notice different sounds! And then some would say that it does work!! Imagine a good quality new bike! The new components like the chain, gears, derailleur etc etc being used for the first time, they would have never of been used together to act as one smooth operation so links in the chain would be slightly loose at first and teeth on the cogs wouldn't of been adapted/worn to the chain to create a perfect fit . But over time these will become balanced and worn with use that all the parts will be tight! If that makes sense? So the same could be said about wires and components in headphones/earphones that when a current passes through a wire for example over time "the burning" it creates less resistance for the electricity current to pass to the dynamic driver or balanced armature to produce the sound to your ears!