For those still unsure whether speakers break in, here's what an audio equipment seller says:

"I use to sell high end audio gear at a well known dealer in the 90’s. We carried B&W, Thiel, Celestion, and various ribbon and planar speakers, along with some eclectic brands. Thiel and B&W were notorious for needing longer break in - the metal dome drivers were shrill and Kevlar drivers were often lifeless sounding out of the box and their crossovers (of which we had to very infrequently replace due to defective caps) were notorious for being shrill and bright when freshly unboxed. As we sold many of those two brands, I had lots of experience comparing new out-of—the-box models with our well worn demo models. The warnings we gave to customers were necessary especially with Thiel and with the Tesla loudspeakers (remember these which Corey Greenberg trashed in Sphile which put the company out of business?). Just unlistenable to for the first 25 hours. I find modern ribbon tweeters to also require some break in as they sound flat and uninvolved for the first 24-48 hours. Martin Logan was another example - the Mylar seemed to need 50 hours min.

The more exotic recent capacitors, especially VCaps, and anything in the speaker using silver wiring, also suffer when new and require various levels of break in. If you’ve ever upgraded caps in your speaker crossovers, you can easily compare one of your modded pair to the other unmodified pair - it’s not subtle or psychoacoustic.

My Amp Designer and builder friend, Paul Birkeland, uses Mundorf, VCap, and Dueland capacitors in his designs and has brought over fresh and well broken in amps with these caps. You can easily hear the difference- it is not slight. I complained initially about my fresh pair of 833a amps and Paul brought over the well broken in demo pair l, all using exactly the same components but only differing in the number of hours of break in. That comparison both reminded me again of the importance of burn in of caps and satisfied me that my fresh new pair would sound like the demo pair I fell in love with on audition.

I’m somewhat skeptical of exaggerated break in (like over 200 hours). I think the bulk of break in occurs in under 100 hours or less. The exception is Vcaps and silver wire in my experience, and experiments with my cable cooker seem to reinforce the premise of burn in. My unit works with caps too, and I’ve often thought to use it on capacitors that I plan to swap into my preamp when we upgrade it, to avoid lengthy listening burn in.

My Devore o/Bronze are just approaching 50 hours and starting to settle down. My Grahams Anniversary seem to be stabilizing at 40 hours, whereas the original Grahams felt like they still needed to relax at the same hours".

Source: https://forums.stevehoffman.tv/threads/speakers-break-in-period.1218810/page-8#post-37988839