amp lights dim

i have a 90 celica with 2 12" l5 kicker solobarics 4ohm dvc(sealed box) on a volfenhag amp (2400 max/800 rms) wired to 2 ohms i have a 70 amp alt wired with 4ga(big3) (+)5ga from battery in front to battery in back 4ga from batt. to amp with a 100 amp fuse. ground for amp and 2nd bat. are factory batt. cables im planning on adding another batt. changing 2nd batt., 3rd batt, and amp ground and most hots to 0/1 ga. also i have a sony 300 something head unit i dont remember. problem is the lights on the amp dim around 10-15/34(vol) and it seams not to hit as hard at higher volums. it used to dim everything(at high vol with a good hit would shut off the car) till i added the 2nd batt. now head lights and radio face dont dim till about 30/34 do i need another batt. or just the bigger wires? also i have a 2f cap which hurt more than it helped with just 1 batt. should i try it again? even if its just as a volt meter or will it just suck power. and most of the time the car is off when the radio is on thanks mike

Well..adding another battery won't do anything if your alternator cannot keep them charged...batteries only help with power below around 12.5-8 volts depending on the battery...anything above that the alternator is providing ALL of the power. I would say start looking for a new alternator if you can. What is your voltage though during harding playing??

voltage when i had the cap on it went from about 14 to 9.50 at times but i haven't checked it in a while and the batteries are both factory spec batteries wired in parallel i think + to +      but now i got a vibration in one of the speakers is that a blown voice coil?