I ordered a 15'' BL dual 2 ohm. I have upgraded 4 gauge from the alt. to my duralast gold battery and i have a 120 amp alt. I also ordered an AQ-1200D. My boy is doing all the installation but he told me to get the dual 2 and wire it at .7 ohms. Will my voltage drop too low?

First and foremost, he is confusing impedance and resistance. The impedance of each coil is 2 ohms, but the resistance is about 1.4 ohms. That's why when you wire in parallel you'll get 1 ohm impedance, 0.7 ohms resistance (aka DCR).

You should probably find somebody who knows the difference between the two before you let them work on installing the equipment.

As for voltage dropping too low, can't really tell before it goes into the car and you monitor it firsthand. But with a 120 amp alternator I think you'll be ok unless you play it for extended periods with the car off or at idle.

thanks bra but i messed it up. i dont know much i always thought it was impedance but trust me he knows what he is doing. thanks for the advice bro

You should be good on the alternator. I run the BL and all my highs on a stock 110 amp alt.

what should i tune it to to hit lows and highs good?

My first box was tuned to 32 and it was great. I started competing and now I have a box that has aero ports tuned to 34 for daily and I change them out to 42 for comp. The 42 doesn't hit the lows like the lower tuning. 32-34 is really great on the lows.