I post here a comment that I found below a YouTube video. I am not the author of it. I found it very relevant to explain the break-in period that many audiophiles consider as a reality...
Guys, there’s no such thing as a break-in period for the speakers. That’s just a period our brain needs to adjust to the sound of any given pair of speakers (or headphones, receivers, preamps, etc.) It’s our brain’s ability (reflex) to adjust to the environment. That’s the purpose of the central nervous system, to interact with the world outside.
We listen to the music through our brains, our ears are just the receptors. Brain does interpretation of the information which comes in from these receptors. It’s been a complex way the musical image has been created. So, with any new pair of speakers, since they have different sonics from speakers that brain has used to listen, it needs time to adjust the way that music should sound (ignoring any unnecessary information in order to assemble the musical image). Literally, our brain learns how to listen to these particular pair of speakers.
An example of what I’m trying to say: Maybe you have friend who listens to his music on a laptop through cheap plastic speakers. Probably he has listened to them for a couple of months. That ‘breaking-in’ has already happened. If you have a decent stereo system at your home, then the first time you hear your friend’s speakers will be awful experience. They will sound like crap, because cheap speakers can’t reproduce the same way your system can. In other words you don’t get the same sonic experience out of these speakers that you’ve been used to with your own stereo. But wait for a while, sit down and listen for a couple of hours, hear some of your favourite albums. At some point you will notice these plastic boxes sound better than in the first minutes you’ve heard them. I’m sure most of you have had such experience with some speakers or headphones. That was an example I’ve experienced on my own. And I gave it because cheap speakers would always sound worse than any good stereo set. With expensive speakers it depends. Initially, some may sound bad, some may sound good. But after some time, they will definitely sound better in our mind. And that’s due to the brain adjustment, not because of breaking-in.
There is interesting episode about breaking-in from Andrew Robinson’s channel here on Youtube. He thinks break-in doesn’t exist, too. How he came to this conclusion? One day a friend of him just asked, ‘Why after some period of time speakers always sound better? Why they never sound worse?’ Watch the episode, it suggests the idea of taking notes during initial and subsecuent listening sessions to justify is there really any difference in presentation.