I want to know if setting a crossover above a certain point on a subwoofer amp hurts the low-end response.

I have a 15". I have my Xover set for about 70hz. Does that seem normal for a 15"?

I didn't have much midbass, that's why I set it higher, but I don't think 15's play well high into the midbass. I will soon be getting some 6x9's to help my 6-3/4's with the midbass.

Also, what is the midbass range? 60-110hz?