Break-in is an interesting topic I am asked about all the time.
I certainly have had many customers comment that our speakers really "open up" after 100 - 200 hours of "break-in." So obviously something is going on here. But what is it?
From all the research I have done, I think I can safely say the following in regard to the drivers themselves. There are two types of performance changes drivers go through with use. The first is mechanical in nature. From everything I have read and the experience of many designers in measuring drivers, this appears to take place in the first 1/2 hour or so and any performance changes after that are very unlikely due to mechanical break-in.
The second is thermal break-in. It takes a very short while for drivers to reach operating temperature when starting cold. This happens every time you turn your system on and start playing music. But this thermal "break-in" happens very quickly.
Based on the above, I would have to conclude that any changes that occur over 100 hours or so are not due to changes in driver performance. Which leaves only crossover performance as a possible physical explanation.
I have never done testing in this regard and have not run across any valid studies on the matter. But it is certainly possible that capacitors do become more efficient in charging and discharging with an extended break-in period. This is pure speculation on my part, but if they do, the increased speed would most likely be noticeable at the top end of the audio spectrum resulting in more micro detail.
I have had the opportunity to A/B new HT3's (after about a 20-minute driver break-in period) with HT3's that were played extensively and, try as I may, I have never been able to discern any significant performance differences. That only thing I have noticed is that the bass quality seems to improve as the rubber surround on the woofer loosens up a bit. However, this would not account for the reports I have had about the speakers "opening up" over time.
I do not doubt that people are hearing what they are hearing and their experiences are real. But I suspect that as they spend more time listening to new speakers, they become more tuned in to subtle performance characteristics they did not notice at first. To the extent that this theory has any validity, it would certainly apply to a speaker like the HT3 which is quite a bit more detailed than the speakers any given listener was likely to have prior experience with.
As I have written in the past, we all have "reference" standards as to what the ideal speaker should sound like and it is based on prior experience. There are many people who are very impressed with the sound quality of a Bose-type speaker system. But as they are exposed to higher and higher quality systems and spend more time with them, their point of reference changes. Some would say they become spoiled (I know I have with the HT3's). We have all probably experienced this first-hand.
I have always felt that this built-in frame of reference changes over time and that much of what is often described as "break-in" is related to this effect. Whether I am right or wrong about this is certainly debatable.
From my perspective, regardless of what the source of this break-in phenomenon is, it is real as far as the listener is concerned. And as long as they are extremely happy with the turn of events, that is all that really matters. Whatever the source of this phenomena, I know that if someone is happy with the speakers the first time they hear them, as with fine wine, things can only get better with time.