Does Equipment Break In, or Does Our Hearing Adjust?

Some equipment clearly "burns in".  Tubes are the best example.  They are metal glowing red hot so it makes sense they need time to reach equilibrium.  Electronics are very small circuit paths in semiconductors and so I can see them rearranging some atoms along the way.  But the time needed to burn it is greatly exaggerated.

It is very convenient for a manufacturer when a customer calls up and says "I don't like the sound, I want to return" and the manufacturere can respond "How long have you listened.  This ___________needs 300-400 hours to burn in."  So the customer hangs up, keeps listening, gets used to it, and figures out 400 hours will take 6 months and after 6 months it is much less likely he will return...oops, lost the box if nothing else.

And I'm skeptical about many things burning in--copper wires for one.  speaker wires, interconnects, and power cords.  The atomic structure of copper doesn't change with low level signals running through it.  Some of these same manufacturers try to tell us they have found directional copper. 

 OTOH, sometimes "burn in" can include the consumption of some alcoholic beverages and on that 10th night of listening with just the right blood alcohol level, this _____________ is now starting to really burn in and sound great.

Jerry

Both, yes. Though for my part, I’ll say I’ve previously underestimated the effect of phycological / hearing adjustment. Over the years now I’ve had two of the same item (one old, one new) several times, which sometimes shows perceived "large" burn-in changes as illusory. Of course this is greatly complicated by the fact that some manufacturers DON’T produce the exact same quality item from unit to unit - even when they’re supposed to be the same version. And then there are products where the maker silently works in minor changes over time (no explicit version change). And then some products - like headphone pads - really do change their acoustics from wear & conditioning.

So I’ll just be satisfied with the fact that BOTH apply, but that actual large changes from burn-in are exceedingly rare.

I once had a guy install new output caps in a custom tube headphone amp. When I listened, it sounded like complete sh*t with no bass and most of the midrange missing. He said: `don’t worry, these caps just take a long time to break in! Get a few hundred hours on them.` Well I got fed up with that quickly, because it was truly unlistenable. So I cracked the amp open and see that he’d put the 0.47uF "bypass" cap in SERIES with the main cap. So even with 300 ohm headphones the high-pass rolloff effect was starting at something like 1 kHz. That’s my best example of "burn in mythos run wild".

I’ve heard interconnects break in.  I had a pair that started out with very tizzy high frequencies and they slowly changed to a more acceptable natural sound over 100 hours.  They didn’t get entirely to where I wanted them but I heard the change, there is no doubt.  I was playing the same song for a week. I knew what to listen for. 

@mward so if you move them around do you have to wait for them to break in again?