Most audiophiles agree that there is a certain “break in period” required for audio gear to start sounding right. Most non-audiophiles will agree that this is the case for something like a loudspeaker, where there is a measureable change in the driver parameters after loosening up a bit, but tend to regard break in phenomena in audio electronics with great skepticism. Most audiophiles point to the usual suspects: resistors, capacitors, and magnetics. This is a good start, but there is a bit more to it.
There is a great exhibit at the Exploratorium in San Francisco. It consists of a basketball, a hoop, and a pair of funky glasses that skew your vision to one side. You start by making a few shots without the glasses – no big deal, the hoop is fairly close. Next you put on the glasses and every shot now goes off to one side – a very strange sensation! However, after several shots you notice that each shot gets a little better as your brain starts to slowly adapt to this new “reality”.
Much like the illusion given by the funky glasses in the basketball exhibit, every piece of audio equipment is nothing more than part of an “illusion engine”. Since the musical reproduction we are creating is an illusion, our brain must learn how to perceive it correctly for the illusion to work at all. This is a significant part of the break in period for audio gear – we are breaking in, right along with the equipment!
Every piece of audio gear has errors, regardless of typical “perfect sound forever” claims. Some errors are easier for your brain to adapt to than others. A longer break in period may in part be the result of errors that require a bit more “training”. Note that the amount of training needed is also a function of the individual. Some listeners may readily forgive certain types of error (e.g. dynamic compression), while being hypersensitive to other types of error (e.g. poor imaging).