It really depends on the driver and how it is used, I would anticipate at least 200 hours before it really sounds "normal". With some drivers its not uncommon for it to take 400+ hours for break in, but typically the first 200 is the real rollercoaster- ups and downs and huge changes in sonic signature.
Replacement Driver Burn-in Time???
I just replaced a woofer driver in a pair of Alon Model 1's (the pair is 8 years old). Does the replacement driver need time to break in? If so, how long does just one driver take to come into it's own?