Why no “Break in” period?

Certain mechanical devices like cartridges and speakers do indeed have break in periods.

Correct

The manufacturers have to remain politically correct or people won't by their equipment.

Also correct

Audioquest believes there is a break-in period that applies to the AQ Niagara 1200.  From their owner's manual:

Though every attempt has been made to reduce the necessity of so-called “break-in,” “burn-in,” or “run-in” time—including high-power run-in of every critical capacitor in the Linear Noise-Dissipation Circuits—the Niagara 1200 will benefit from continuous use, just like any other audio/video component. This is not to say that you will be made to “suffer” through weeks or months of intolerable performance until that “magic day” when the parts are fully formed and ready. On the contrary, the Niagara 1200 will perform very well from the first moment you use it. It will improve gradually, in small increments, over a period of approximately two weeks. While leaving the Niagara 1200 turned on during this period will aid the process, it is also perfectly acceptable to turn the unit off; doing so will simply increase the time it takes to reach final “break-in.”

@millercarbon gave you the correct and accurate response.  The rest of the thread is superfluous, with people using it to grind various axes.

Duelund capacitors are said to take, what, 600 hours to break-in. O...M...G 😱

For many years my "expectation bias" was rock solid: wire is wire. Digital is perfect. There’s NO difference between CD players, DACs, wire, and most definitely the last thing that would ever make any difference is something as stupid and senseless as putting a cone under it or a weight on top or anything like that. Sheer, utter nonense.

Until I took the time to actually listen and compare.

So yeah people are biased. Duh. But there is expectation, what we imagine we might experience, and then there is the actual experience itself. To put one above the other is to be confused almost beyond belief. Its like saying you’re some kind of robot: mindless, programmed, unable to adapt or change.

Which, come to think of it, all things considered, could well be you are. If that is what you think, and think it long enough, after a while that is what you are.

Now as for how long this takes, well there are things like tone and volume I just seemed to always have been able to hear. If a speaker cab is woody, or the bass is bloated, or the top end tipped up, pretty much everybody is able to notice this right off the bat.

The differences between CD players, cones, amps, things like that, the differences are there, only they tend to be of a different character and usually much more subtle. I’m writing for the guys who want to learn this stuff. Because listening is a skill. Like all skills it can be learned. This is not easy. Does not come naturally. It takes work.

So 6 to 12 months? Yeah. About how long it took me. During that year or so, often times took my wife around to shops and it usually went something like this: Yeah that one WAS better! How? Don’t know. It just sounded richer, more expensive. Which is funny. Wife says it "sounded" more "expensive". (Her words.)

Only much later on was I able to break it down into darker backgrounds, more palpably solid presence, micro-dynamic shadings, sharp but not hard transients, beautiful trailing decay and ambience, depth and layering, air and space, etc.

Now having developed those skills, it don’t take no 6 to 12 months. Six to twelve seconds, maybe.

This past year I’ve been on a tear, adding Herron, Koetsu, CTS, Euphoria, and more. Every single one of those gave immense listening pleasure as they sounded great right out of the box and then proceeded to open up and improve minute by minute, then hour by hour, day by day, until finally stabilizing some weeks later.

Well after all every single night I have to endure listening to the first side, as no matter how well everything else is warmed up the cartridge and phono stage still improve massively the first few minutes. The second track is a lot better than the first, the second side better than the first, and then it slows down a lot but still always continues to improve well into the night. You go to sleep with that wonderful late night sound in there and oh how I wish the "you can’t remember" crowd were right because then I wouldn’t have to endure the first side thing all over again, night after night.

Anyone thinks this is nuts, based on their own inability to hear these things, all I can say is keep at it. You can get there.