What are we listening for during break in?

Grannyring, you are passionate in your belief. As I've never experienced it, I have a hard time understanding and therefore believing a wire changes its sonic characteristics with a hundred hours or so of use. If it does change after break in, does it always change for the better or have you ever heard one get worse? If they always improve there must be some reason, why would that be?
As stated in original post, I have experienced sonic changes in new speakers after break in. It wasn't subtle. I also believe not all components sound alike and I have heard a difference between speaker cables. Maybe I don't listen close enough to new cables to notice a change. In fact I know I don't listen close enough as I'm not sure what I'm listening for.

Point one- I have long since abandoned A/B testing thanks to the late great Harvey Rosenberg. I tend to know what I want when I hear it. I keep it till I tire of it,it wears out or becomes obsolete.

I assume everyone has a reference that is the sound of thier own system. Some claim thier reference is live music but they are usually deluding themselves. When you install a new component you have to form a new standard.

I have yet to hear any credible explanation of what part of the cable is being burned in. This differs from moving parts, tube or caps,etc. Maybe a power cord generates enough power to burn in. Not interconnects or phono cables. Monster amps get hot but that heat never seems to make it to the speaker cable.

I have no way of disputing what you heard. It certainly differs from my experience. No harm comes from burning in a wire unless you purchase a burn in cd. In case you will be out whatever you paid. Everyone should have some type of frequency spectrum cd or lp to assist you in spea ker placement. That will do just fine.

You may have deduced I am a cable skeptic. I'm definitely fro

I'm a "no cable break in" kind of guy too.

I understand speakers (there are physical changes in the cones & surrounds).

Perhaps, I can understand electronics (manufacturing aids flashing off, cap's fully charging, operating temperature changes...).

Don't understand cable break-in...

although a cable's sonic character may change a little over time, the basic 'sound' or 'signature' remains.

There are two issues here, and they are being conflated.

1. Do cables require break-in?
This is unlikely to be resolved for more than a few who have not yet formed an opinion. Lots of sincerity, mixed with disbelief, bombast and outright belligerence on both sides usually emerge on this. Strength of opinion does not equal truth. This, though, does not seem to be what the initial poster is asking.

2. What "sonic differences" are heard? "Better, worse, different?"
These were the questions here. The answer seems conmplicated and simple.

The complicated part: For those who believe (the operative assumption here) that different cables have distinct sonic signatures that justify auditioning, switching, system matching, and the sometimes surreal cost of some cables compared to standard cheapo rca's, it seems quite likely that different cables will sound one way or another initially. How can you say what you're listening for generically, without reference to a particular cable in a particular set-up (including room)? Do all cables have the same sonic limitations when new? Do they all change at the same rate and in the same way? I don't see how any empirical "proof" could be generated with the extraordinary number of variables that would be present, and this is without the input of cable and break in doubters who will surely step up to the plate.

The easy part: Set it and forget it until some break in mile marker is reached. Establish some sort of input to output set up that can be run non-stop and check it at some time interval that seems acceptable to you. Check it periodically to see how it sounds to you. Ignore it most of the time until it goes into its place in the system or is returned.

I described making a break-in thingy for a phono cable that had a right angle din plug using a tuner and pre-amp in another post on Audiogon. I made this because a protracted break in was claimed for the cable, and I didn't want to go through several hundred album sides deciding if I wanted to keep the cable. Perhaps it made a difference; perhaps I might have heard it and noted it at LP side 1 vs. side 50 vs. side 143, but listening for such nuance in break in just wasn't a worthwhile activity for me.

What listening for in break in over various time intervals might be worth to the original poster or anyone else is up to them. You might or might not be able to hear a difference. If it is of interest to you, fine. I certainly know that it's not worth anything to some.