What is "break in" and what difference does it make? In amps? Preamps? Speakers? More?

Sorry to ask a question that’s been asked so many times. If it were possible, I’d just delete this question and try to come up with something more novel. But I suppose people can just skip answering it. Or give 

You’ll get as many opinions as comments on this, my personal experience is most break in is between the ears, you get accustomed to the sound. President and designer of a speaker company told me that would be the case with his speakers as they are played for a couple of hours before shipping so I wouldn’t notice any mechanical changes. My opinion is it might take a few seconds to perhaps an hour for all the electronics in a component to " break in" of course it takes tubes a while to heat up but other than that I never think of or worry about break in but some say they can hear a fuse or a mains cable break in, I never have.

+1 djones51!

Have you tried candling your ears recently? 🕯

Is there a difference in what one hears when it comes to speaker break-in vs. component break-in?

Not really. All start out with whatever fundamental character they have, but thin and etched or grainy, and then over time fill in and round out becoming more palpably real. To whatever extent they are capable of doing this. The differences are only in the details. The over-arching fact of improving with use is the same regardless of whether we are talking about a speaker or cable or component, or even a part like a fuse, cap, diode, or transformer. They are all the same.

Are there levels (quality) where break-in makes no difference?

No.

There are levels where some are run in before shipping. But no one is going to run anything 24/7 for 30 days- and even if they did it would still go through a mini break-in when first hooked up after being banged around in a cold shipping container for who knows how long. Just like every night the gear you had turned off during the day takes a while to warm up and sound its best, so everything brand new goes through the same process, only more so.

Hard to believe after all these years there are still people questioning this. I’m not talking about the OP, who we can excuse for being new. I’m talking about these others still pretending what is staring them right in the face is not really there. What is wrong with audiophiles???