You need a large capacitor for the subwoofer, higher output alternator won't help for that symptom.
A capacitor is like a quick discharge battery, it stores "volts/amps".
Here is what is happening in your vehicle.
After starting the engine the alternator will re-charge the battery with 14.8volts, after a few minutes voltage will drop to maintenance voltage and the system should be 13.6volts, running system above 14volts will damage battery over time.
This change in voltage is done by the voltage regulator in the alternator, when you turn on the lights the voltage will drop to 13.3volts then quickly come back up to 13.6volts, that is the voltage regulator reacting to more power being needed so it sends more amps/volts.
If you turn the Fan to high, same thing will happen, voltage drops, regulator gives more volts to system.
With a subwoofer the power draw on a heavy bass note is not constant, voltage regulator can not react fast enough, it does react, just not fast enough.
So even a bigger alternator would suffer the same fate, the quick voltage drop and lights dimming.
A capacitor at the subwoofer stores voltage/amps when there is plenty in the system, and when there is a sudden drop it releases some of it's energy so voltage drop is never seen on the vehicles electric system.
If your lights were dim all the time and car wouldn't start any more because of the sound system power draw, then yes a bigger alternator would help.
A 1 farad would be all you need for 750watt, $20-$30, 2 farad is $30-$40
They are very easy to hook up,
The closer to the amp the better, but it isn't that important
Last edited by RonD; 06-26-2014 at 09:24 PM.