Upper and lower range means that the speaker is capable of producing those frequencies.
-3(some even go -2) is the norm used. 3db is "twice as loud". So...
-3 at 65hz means it is "half as loud" as its mean point(usually somewhere along 1khz).
Unless a manufacturer provides an actual graph(or you create your own with sine sweeps) it isn't of much help, other than setting your crossover in an AVR. Which this speaker could be set at 65 or 70(depending which choice your AVR gives you)...or left at 80.Go to the full post