Do you think driver “break in” is real?


Do you think “high end” drivers and crossovers typically need a “break in” period before they sound their best?  I ask because, I believe I’ve experienced this first hand in a very significant way. I replaced the tweeters (same exact brand and model as original) in my ACI Sapphire 25 year anniversary edition speakers and for the first week I thought I’d lost my all time favorite speakers. I was depressed!  So I just kept playing them…  finally after a couple weeks, I’m literally stunned and blown away at how incredible these speakers sound. Completely different than the first 30 or 40 hours after I put in the new Scan Speak tweeters. So I say break in period must be real - at least for some drivers. Has anyone else experienced this to a degree that is unmistakeable?  
Crossovers too?  I just rebuilt the crossovers for a pair of ACI Sapphire XL’s (using highest quality components- same values) and so far they sound mediocre. Hoping for the same result as my other Sapphires but after about 20 hours - no noticeable difference - and they do not even sound as good as prior to crossover rebuild. They sound flat, too bright with poor imaging - but for 10 to 15 years they were pretty great sounding speakers. Thoughts on crossover break in?? 
Thanks to anyone who responds!!  

sal1963

Yes unless you bought crap speakers.  With crap speakers the speakers still need to break in but still don’t sound good. 

No. This has been measured many times. Part of the myth is so you won't return it immediately and you'll get used to the sound of your new speaker.

There's a very long post at Audioholics, which I suggest reading the end first.  They don't say driver break in isn't real, but that it happens very quickly and once it occurs there's no need for more:

 

In an electrodynamic driver featuring the usual surround-diaphragm-spider construction, driver suspension mechanical compliance plays a key roll in determining the measured value of various driver parameters. All of these parameters will shift as the mechanical compliance of the driver's suspension shifts in value. The bulk of a driver's compliance shift will occur at the time of initial burn in.

Subsequent shifts in compliance are largely temporary in nature.

https://gr-research.com/driver-burn-in-facts/

Danny Richie includes multiple measurements of drivers at differing states of burn in / use. This article would certainly support that drivers do "burn in" over time.

The manufacturers of some of my gear have indicated on the manual how the gear will change sonically after X amount of hours.

Yes of course speakers need burn in time. One hi fi dealer advised me to use burn in cd from Purist audio design and it really helps to reduce the time.