It's the first resonance frequency your port will make noise on other than what it's tuned to more or less. You want to cross over well below this region to make sure it's not audible. Unless you tune very low so that your port tuning and it's first resonace are in the woofers bandpass then it's a non-issue. As far as your graph, I have no idea what kind of output or sound your looking for so it's hard to say. Looks like alot of bloated low end to me, so if that's what you wanted then it looks fine. you should go get winisd alpha, much better program even with it's bugs.