Not to discredit Mike in anyway, but most subs do need a bit of EQ'ing to be flat. If a subwoofer can do it without EQ and have high excursion like a SS RL-p, then that is pretty darn amazing but it won’t be flat once you put it in a room. Remember, EQ is not a bad thing, in fact, once a subwoofer is flat, you can pretty much neglect everything else and pass it off as a pretty darn good sounding driver (unless a piece of nasty sounding junk with lots of THD from the get go)
Everyone of our customers who uses our drivers in home theater will EQ them here or there in one way or another and I always recommend to our car audio followers that they invest in some modest measurement equipment like a 50 dollar mic or dB reader to be able to flatted out peaks or valleys in the frequency response in whichever environment they put their subwoofer in. In fact, even a flat sub in free air or IB, will probably be un-flat once you put it in a box, and then after you get that flat, you will again, be faced with problems in whichever room you place the subwoofer in as reflections become the next challenge. It’s always good to have some kind of PEQ if you want the best sounding bass experience regardless of which driver you choose
