ever heard of a phenomenon called resonance? two subs tuned at different frequencies with their slopes overlapping each other will give peak to some frequencies and will cancel out others. now u can equalize the hell out of them and get into more trouble or simply use one sub.
let me explain it in simple words to you. you have two different type of subs. you are using em to produce two different frequency ranges. at a point in time sub A is at its full xmax and sub B is at its tuning frequency which means that the movement of the cone is minimum. you will have two subs that are out of phase with each other. your sound quality will drop and u will have certain peaks and certain drops in sound. not a good thing
in ur screen shot u have boosted up 50hz and 100hz freqs... but do tell me.. have you managed to somehow a signal of up to 50hz to one amp and another signal of 100 amp to the second amp? and if you have, do you notice the dip in the 75 hz region? so now are you going to add a third subwoofer tuned at 75 hz? and even then, having such peaks in the sound is not exactly musical is it? be it for one's own listening pleasure or for people on the street's.
even put in simpler words... wiring the polarity of one of your speakers in reverse takes away all the bass and gives you a hollow sound. you are talking abou two different subs here which in many ways is same.
