This completely mirrors research performed at Harman where they tested a new woofer and a "broken-in" one in a real speaker. While physical changes are occurring in the driver, they are at such low level that there is no hope of attaching them to audibility.
These statements are consistent with my experience.Speaker break-in is very real and very measurable, but in most cases will still not be audible.
A really good chassis or loudspeaker shows almost no measurable break-in.
To underline this, here is an example. On 12-2018 I finished and measured a bass compartment (called "Troll-Base") with the Dayton RSS390HF-4.
Today, more than a year later, I measured the bass compartment again (the chassis was definitely broken in over the year, because my 500W power amplifier is clipping regularly ).
First of all we look at the impedance curve with the new chassis/loudspeaker (yellow curve) compared to today (green curve).
It's nice to see that the resonance frequency of the entire loudspeaker has not changed at all. I wouldn't expect anything else from a really high quality driver and the RSS390HF-4 is one.
If you take a closer look you will notice slight changes in the range of 100-300Hz and around 800Hz.
Next we look at the near field frequency response of the new chassis/speaker compared to today.
Since the "Troll-Base" is responsible for the low frequency response in several possible 3-way combinations, a range of use up to 300Hz (maybe even up to 500Hz) is planned. (new chassis/loudspeaker - yellow curve, measured today - red)
If the chassis would be used as pure sub-woofer, there would be no change at all.
In the free field with the influence of the driver cone and the baffle of the loudspeaker, a small change around 220Hz might still occur. Will this change be audible? In this frequency range rather not (in addition, in many living rooms the Schroeder frequency is around 200Hz, so room modes further reduce audibility).
So a speaker that sounds like crap will not mutate into a high-end miracle even after 100 hours of use - send it back.
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