when i bump my single 12" kicker with the headlights on, all lights dim when the bass hits. will a optima battery or a cap relieve this ?
Yeah, I have both a yellow-top Optima, and a 1-farad power cap, and a 700-watt 12"… it doesn’t COMPLETELY eliminate the problem, but it’s so much better now…
what amp do you have and which sub? youre driving your amp too hard. turn down the gain. want more power? get a better amp =/
learn about gains http://www.eatel.net/~amptech/elecdisc/gaincon2.htm
basically, turn all bass/treble/loudness controls to zero. turn deck up to 85% volume. slowly turn up amp gain until sub distorts, then back down slightly. done.
caps/batteries are only for when the car is off. A stronger (rewound) alternator will actually heal (not bandage) the problem. You can get your alt. rewound for less than the price of the Optima, in most cases. Also, do a search on here for what wires under the hood to upgrade to larger guage (I recommend 2 or 4 guage).
→ battery ground.
→ alternator ground.
→ alternator-to-battery
→ engine block ground (like 8 guage or something).
This will allow every bit of juice to get to your amps. I have a DEI 1100D and a Premier 450 watt amp (GM-X822) running in my car and NO light dimming unless it’s at about 90% volume (that’s over 1400 watts of power). No deep-cycle battery, no caps, no upgraded alternator. Just big fat wires under the hood. 
~Eric
another q. how bad is headlight dimming? is my car like gona just die or something ?