I'm going to really stir the pot with this post.
My Dali Megalines required 450 to 600 hours before they performed to their maximum. The bass was non existent until after 300 hours and deep bass not until nearly 600.
A good friend and member of my audio group experienced similar frustration with his Kharma Exquisite 1De. He waited beyond 650 hours before his speakers produced best performance.
In both cases, I have ten or so associates that heard the long progress and final results. Believe it or not, it's absolutely true.
Maybe it's the ceramic drivers in the Kharma, maybe the 24 woofers in my Dali's move so little that break in is tardy in arriving. Whatever the reason, it's audible and frustrating to wait through.
My new tube crossover made a break through in performance this last Tuesday evening. Burn in was 605 hours at the end of the evening and a huge change from the week before when there was only 437 hours on the parts.
In the case of the crossover I know the slow break in is due to Teflon Caps, 14 in the main unit and more in the power supply. I called the manufacturer who designed and built the caps (the same guy that builds Cardas, V-Cap, DynamiCap and most of the other big names).
He was not surprised, said it would continue to about 1000 hours or beyond, same answer I got from several other engineers in the business.
My previous custom crossover was identical in design, hand built by the same guy and was working well at 50 hours, reaching maximum performance at about 350 hours.
The difference? It had traditional caps from Wima, F-Dyne and Illinois capacitor and half the chokes and power supply. Everything makes a difference when all the parts are pushed to the limit.