Dave,
This is a subject I've avoided for the most part, primarily because I buy used drivers to
save on taxes and duties down here that essentially double the cost of new drivers. Also,
I always want stuff to sound it's best right off the bat, so I loosen up woofers with LF tones
and stick tweeters in a heavily dampened box to play HF through them at silly SPL's overnight.
These efforts should be enough to loosen up surrounds and spiders, so T/S parameters should
be stable afterward. This addresses the short-term "fresh out of the box" break-in that almost
no one argues about.
Then there's the subject of long-term break-in. Anyone who's modified the cone of a driver in
any way can tell you that anything you do to the cone makes a sonic difference. The best
explanation I've seen for long-term cone break-in is that, especially with paper cone drivers,
the fibers in the cone rub against each other as it flexes and bends (they only operate like a
piston in the lower frequencies). The sonics of this rubbing changes over time, like a new pair
of jeans which become softer over time. This explanation seems to make sense. For a comparison
take a new piece of paper. If you bend and flex it, it makes noise, but if you do it for long enough
the sound greatly diminishes.
With my Fostex FE206's that I used daily for about 9 months, I thought they did become smoother
over time, however, now when I occasionally put them in my system, after the first few minutes
they sound just as obnoxious to me as I remember right out of the box. Those first few minutes,
though, the sound does appreciably change as they warm up, which didn't happen when they were
new. I don't know what changes when drivers go unused for a significant period, but it's definitely
audible. It's similar to a tube amp that is used infrequently. Sometimes when you turn it on it can
sound absolutely terrible, and even warmup doesn't help, but a few on/off cycles with warmup does.
On the other end of the spectrum are my Hawthorne SI coax's. I'm more confident that their sound
changed over time than I am for the 206's. Also, when I don't use them for a while, they don't go
through the same few minutes of change as the 206's. The cone structures of the 2 are very different.
The 206 has a very thin rigid cone, and the SI coax woofer has a much larger and thicker fully ribbed cone.
The flex in the 206 cone is determined by it's rigidity, while the SI cone flex is determined, at least in part,
by the geometry of the ribbed structure. Neither can change very much with use, otherwise they would
just quickly fall apart.
An analogy of why break-in affects one more than the other is a pair of jeans vs a starched 300 thread
count cotton shirt. Blue jeans definitely break-in with wear and washing, but the starched shirt feels
virtually the same every time you wear it.
That's my 2 cents on the subject. Yes, I think break-in over time occurs with drivers, although I'm up in
the air about it's audibility, and if it does occur, then it varies with different drivers and cone materials.
