The rule of thumb for pickin caps is about .5 Farad for every 500W rms. So for 1200W you would need about 1.25 F for each amp. You could probably get away with 1F as long as you dont crank it all the time. If you do crank it all the time - It wont matter what you pick 'coz at 2400W goin' to 2 fifteens you'll be stone deaf in about 2 months so save your money for the new phone your gonna need.

-ToK