Originally Posted by cptomes
...Not to mention the fact that in a lot of decent audio equipment the power supplies are actually the most costly subassemblies. Which are specifically designed to deal with issues on the mains.
Ten internets for this post!
Anyone that builds their own gear knows that step one is to build a proper power supply to provide a clean signal to the rest of the rig. Anything a properly-built power supply cannot rectify needs to be rectified through power conditioning, and that would have to be quite severe.
My advice for those that want fancy looking power cables is to buy some nice looking terminals, some braided wire sleeve, some heat shrink, and go to town. My advice for speaker cables is only slightly more advanced. Neither will burn in. The electrons will happily travel from the very first second.
As for the OP's question, I can't add any measurements, unfortunately. My measuring tools are old-school and low-tech. I always break in speakers because I feel that the surround is stiffer out of the factory, and needs to be worked in a bit. To me, the bigger drivers do seem to sound different after the surround softens up, but I've never measured.
I also like to burn in new tubes for a number of hours before I give them any critical listening. I believe
that there can be some seem to change in dynamics after being warmed the first time for a handful of hours, more notably for me with some of the NOS Russian and Yugoslavian produced tubes I've tried. But again I've never measured. And my ears aren't acute enough to detect any changes after that initial heating cycle (other than when they're not warmed properly). These changes are subtle enough that they could
Certain components, such as some ceramic disc capacitors, are known to "age" over time, gradually changing in property. This isn't a "burn-in" phenomenon, just gradual aging: a continual decay. Sometime such components can be included in builds that are initially over-spec, so that over time they age into a more appropriate range. This would be a very slow process - occurring over potentially many hundreds of hours. Not what I would call "burn-in", but I suppose one could argue that point.
Some of these same components also suffer from measurable changes due to operating temperature, so would measure different when first turned on versus when warmed up to "working" temperature, but again this is not a "burn-in" issue.
Others argue that it's possible for a freshly-soldered board (or component) to need a good heat cycle to "re-flow", which is said to improve the connections hence potentially change measurements. I'm curious how much heat would be required for such a change...