Audio Systems: what alternator do i need to run my system?, quality batteries, farads

Question
I'm trying to install a sound system that will be running about 4000 watts, but I'm afraid I will blow out my alternator. What kind of alternator will I need to get to run that much power, and is a second battery a good idea?

Answer
Well it depends on what kind of car you have.  Upgrading the stock alternator is not always needed.  With 4000 watts I do recommend adding at least 1 if not 2 good quality batteries, such as Optima yellow tops, or a good quality car audio specific battery like Kinetic.  I would also recommend you use at least 5 to 10 farads of capacitor.  Remember a capacitor is going to react more quickly to peak draw than a battery or alterator will.  Having extra capacitors will take load off of the batteries and alternator.