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!!  


Put on a new pair of jeans, or shoes.


not so comfortable. After a couple of days of use, they get better. 


Break in is very real. As an avid DIY builder of audio gear, it’s obvious to me how much benefit a driver will have from  break in over time.

As a similar analogy, consider a new automobile engine: There’s a reason you’re not supposed to over-rev the thing until so many hours have passed.

i agree that break-in periods are difficult to empirically evaluate due to our familiarization with the sound over hundreds of hours.

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However, you can rev new speakers as much as you wish without damage. Just change the oil regularly.