I will try and answer it Ben - not because I know the answer, but because my experience of break in and different people's opinions on it seem to converge on a particular conclusion, in my mind.
First, I believe that both component and psychological break-in occur. But I cannot prove either.
I have experienced the phenomena of a CD sounding odd on first listen and then sounding more 'right' after a few more listens. I believe that this is not due to anything else changing than my brain getting accustomed to decoding the particular distortions on that CD. I believe that this is essentially what the brain does when it processes sound information it receives from the ear. It tries to correlate it with sounds it is more familiar with and then decides to 'hear' the sound in a way that the brain has determined is the sound of the true event.
This is a little like the way when you record music you have to keep the sound of the recording acoustic low in the mix. I believe the brain finds it easy to keep the sound of reflections out of the way of the sound of the source of that sound when it is in the same acoustic environment, but when listening in one environment, to an event recorded in another, the reflections in the recorded acoustic are difficult to put aside at the same time as putting aside the acoustics in the current environment. This is why you hear lots of sound reflection when you listen to a simple recording of your voice.
So when I hear a new CD - I am not saying the issue is reflections, that was just an analogy - my brain takes a while to get used to hearing past the distortions that are unique to that particular disc.
I have no doubt that this happens when we hear a new stereo system or just a component change to a new stereo system.
But I do not accept that this phenomena explains the changes I hear while a component breaks in. The following observations are what I base this on.
- I don't hear CDs change their sound from thin brittle and bassless, then thick and murky, then hard and edgy, suddenly soft and mushy and then finally sharpen up to sound about right, in the way that some new components do. The alternative explanation is that the distortions of a component are manifold and my brain learns to decode them one at a time and so the sound moves around each time it deals to a particular type of distortion. Maybe.
- I take much less time to decode the sound of a friend's system than I do to decode the sound of a new system I put together. The alternative explanation is that I am either less critical of my friend's system than when my money and future musical enjoyment is at stake, or I am just atrocious at putting systems together such that my brain needs way longer to deal with it. Hmm, unlikly Ben, and fairly conclusive evidence for component break in - in my mind.
- Whereas when taking a CD out of the system for a month or two my brain has no trouble finding it to sound like the last time I heard it, taking a cable out of the system and curling it up in the cupboard for a month results in me hearing a break-in occurring for anything between two days and two weeks. The alternative explanation is that the distortions of a cable are more complex for my brain to decode than the distortions of a CD. The measurement freaks will have trouble with that one.
- I also respect the validity of other peoples' conclusions from their experiences, not just my own. I observe that many who claim that there is no component break in also state they hear little or no change during break in, and that many who claim that component break in exists, also state that they hear significant differences during break in. This is explained if you accept some people are more irritated by the distortions that go away as a component breaks in. The alternative explanation is that some people have brains that immediately decode the distortions in a new system and others are handicapped in this ability and take 300 hours. Being biased I don't like the thought of being handicapped in the brain department, so you can guess which one I prefer.
- The 300 hours burn in is the most persuasive point for me. How come the burn in appears to occur whether we listen to it while it is burning in or not. The alternative explanation is... we are deluded by our prevailing belief in burn in, or I guess we are just lying to prove our point. I can imagine how you could make that assumption. But you can imagine why I don't.
The interesting thing is there seems to be a correlation between those that deny burn in and those that believe the component that makes the most difference in a stereo system is the speakers. In fact I find this very interesting. I suspect we listen for different things, have different musical values or simply are irritated by different distortions. You see I find most speakers that survive commercially today in the high end are capable of sounding musical. Whereas I cannot say that of amplifiers - the very opposite of what the measurements would lead you to believe. Therefore I strongly suspect that there are distortions that irritate me, and many like me, that do not pop up as significant in conventional measurement (which pro-rates distortion issues rather liberally), are endemic in electronics and less measurable than speaker mechanical distortions, and that reduce dramatically during burn in.
Finally, I have experienced components sounding more pleasing in tonal characteristics during burn in than after burn in - but there is nevertheless something else wrong during burn in. Perhaps it is a form of phase distortion that upsets my brain (and others like me).
