Given the choice between to subs, what would you recommend (I have experience with Infinty but not Rockford Fosgate)

I will be running 4 of these.

Infinity Reference 1062W

Rockford Fosgate P2D410

I did ask myself that:

I am currently running two JL Audio 15W0V3-4 (which I love !) in a ported box for the deep rich base, but am also adding some 10's in a sealed box to give me better punch base, but I need dual 4ohm VC and JL only has single in that series, I like good sound and want to be loud but am not enetering and SPL contests. But I am on a budget so I like the Infinity and have used them before. I also considered Diamong Audio D310D4, but they are a bit more $$$.

also, I alread have the box build to Infinity specs for 4 each and IN the car (waiting for $$$ for the subs)

I would go with the JL if I could get 4 of them to total 2ohms.

well i guess ill start by saying that good sound is in the ear of the listener. now your goal is to use an array of 10's and and 15's to theoretically get the best of both worlds. you want the "deep" bass of the 15 and the "tight" bass from the 10's. first of all, how a sub sounds is pretty much laid out by how it is built and which materials its made of and the design of the box you install the sub into. ive heard plenty of systems with 10's that sound just as deep as any 15, they just usually cant compete volume wise so you end up needing more 10's v.s. only one 15.

you will be using different subs, of different sizes, with different specs and designs, and running on different power, and mounted into boxes that will have different properties. unless you can actively filter the signals going to each set of subs so that the 15's are set to play only the lows and the the 10's set to play only higher frequency bass and then design the boxes so that the output blends at your crossover point then you run the risk of your subs cancelling eachother out, echoing, hiccuping ( because the pressure from the 15's will win the battle with the 10's when they hit causing them to move when they should be doing something else) its already hard enough to propperly set up a multi subwoofer system and you are just making it even harder by missmatching your equipment.

now with that said, will it work? yes. will it be louder than what you have? maybe but theres just as good of a chance that it will actually not be as loud. will it sound good? thats for you to decide but only after you have spent all the money time and effort just to find out everything that ive just told you so go for it cuz you gotta learn somehow... 

My plan was to x-over the 15's at 50hz and the 10's at about 70-75, but what you are saying is to have an active crossover on the 10's also that will keep it above 50 and below 75?

I have decided to go with same same everything, so all subs and amps will be JL, I am just going to use another JX1000.1D for the 10's at 4ohm load total and push only 500watts to them.

If I ran all subs at the same x-over and with the same (but bigger)  amp would that be better or worse than what my plan is above??

or should I scrap the 10's idea and do 2 more 15's?

yea if you wanted to run the 10's then you would have to run a bandpass filter on the 10's and a lowpass on the 15's so that they dont interfere with each other. but really you would have to do this either way you went if you want to run two subs ported and two subs sealed cuz no matter what you wouldnt want them trying to play the same notes.

see below

one question:

we used to do this all the time (back in the late 80's) I had a mini truck with 2-15's downfired behind the front seats, and 2-10's in the back window (had a shell on the bed) and it "seemed" to sound fine back then, my friend had 2-15's and 4-10's in a wall in his car, and it "seemed" to sound fantastic.

So what am I missing?

Anyway, I have re-thought my system based on these finding and I will be going with 4-15's (Diamond Audio D315-4) in sealed a enclosure with 1.75 cuft per sub, all wired to 1 (for now) JL Audio JX1000.1D at 2ohms