Factory Break In, What Is It?
FBI is a process of exercising the speaker with a variac set to a particular voltage to match the speaker's ohm and power handling.
It puts a 60 cycle tone through it that moves the cone about 1/4" up and down. Cycles are 2 hours on, 1 hour off to cool. I do that for 8-9 cycles, or 24 hours total (18 hours on). Since it breaks the speaker in three times faster than you can do it by playing, it replicates being played at 30-40w on stage for 40-50 hours.
At the end of it, the speaker responds with better bass and low mids, a slight reduction in treble to offset sharp tones, and fills out the midrange.
About 80% of my sales are combined with FBI, including repeat clients, so it works great! If you're not going to get to play at 30w for 40-50 hours in less than two months, I highly recommend it.