Dayton AMT tweeters change sensitivity over time?

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I built a new crossover for my Dayton B652 Air bookshelf speakers. At the time it was well known that the treble was hot and it was common to increase the tweeter resistor to compensate.

I used one speaker constantly and the other was used a bit but not much.

Now I measured the frequency response again and the treble is down 5db. The DC resistance has not changed. I measured the unused speaker and it is the same way! I tested my microphone, as far as I can tell it works the same as it did when I made the crossover.

What this means is that either both woofers have increased in sensitivity by 5db (unlikely as sensitivity is set by the mass of the cone, strength of the magnet and number of turns in the coil), or the tweeters have lost 5db of sensitivity.

Now when I change the tweeter resistor back to the original 4ohm value, the sensitivities are matched.

This suggests to me that Dayton already knew these tweeters would lose sensitivity over time and that is why the treble is hot out of the box. Furthermore I don't think they ever explained this to anyone, although they presumably easily could have.

Has anyone who purchased a Dayton mini-8 AMT measured an initial sensitivity higher than what is in the specsheet?
 
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