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

@erik_squires - indeed, once broken in, a speaker should perform how it was designed to perform and no more playing will increase the performance.

I dunno about that 'very quickly' part, though - that's not been my experience with either speakers or headphones, but I guess it depends on how you define 'very quickly'. I give 'em 150 - 200 hours before I judge them, though some need less.

My loudspeakers required about 300 hours of use to fully impart their coherence.  

For some woofers yes, they do loosen up a little. For planar magnetics and ESLs most definitely. Their diaphragms are tensioned with a heat gun they then relax to the right tension. Some ribbon speakers will actually relax to much in time and require ribbon replacement. 

@erik_squires  Exactly. Within minutes. Certainly not the "break-in" that people talk about or need to worry about. Several custom speaker builders and kit makers have run this test on drivers so they could get accurate "broken in" specs. I read the first one about 20 years ago. I believe it might have been a kit maker whose name escapes me, but it began with a 'Z'. I believe they shut down years ago. Another who did the measurements was Bill Fitzmaurice.​​

Part of the myth is so you won't return it immediately and you'll get used to the sound of your new speaker

I can't imagine getting used to a speaker I don't like. I can imagine a speaker growing on me though that I like from the moment I hook them up.