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There are a few benefits to using a cap in a daily driver. The cap installed near the amp is able to discharge faster then the battery upfront. This allows for less strain on the alt. due to the fact that there is less resistance compared to pulling the same amount of current all the way from the battery (resulting in a lower voltage at the amplifier). The cap will recharge quicker then any of us can measure so don't worry about it only helping the first hit. One major problem is most people that need a cap are usually maxing out their amplifiers consistently, as opposed to someone that uses them to "critically listen" to music. When the gains are set properly the amp is very dynamic, some beats on the drum are not as loud as others, and you can tell the difference. In that scenario the cap helps on the big swings. When pounding down the street with a bass CD in, the amp is not "swinging" at all, it is constantly using everything it has, and this is using more current then the alt. and battery want to give up. This is why your lights dim on every bass note. The chance of a 1 farad cap helping this are very slim to none. The reason is the alt. can't keep up and charge the battery and the cap. A bigger alt. would be the way to go. Or for a quick fix add a second battery in the trunk. This will help with the lights dimming and put more power in the back (because it stores more energy then a cap). You still have the problem that the alt. cannot put out enough juice to properly charge both batteries (that means charge them and maintain them at 14.4v) The trade off here is the same reason that the caps don't work for SPL-----
The extra battery and the cap both become a load to the alternator.(just like your amp is a load on the battery and the alt.) So the alternator basically "bogs" down and the operating voltage will be lower with more "loaded" on it. Your spl numbers will go down as the voltage goes down (NOT AS NOTICEABLE WITH A TIGHTLY REGULATED POWER SUPPLY). This is why most guys in street class gain almost a dB when they take out their caps. They have raised the operating voltage of their amps.(remember this is only for a short burp).Much in the way that ss and extreme guys "up" their voltage to get more power out of their amps.(remember that an amplifier steps voltage up inside so 1 volt difference can be a lot of power------ 12v in x3=36v+ and 36v- =72v across speaker leads now square that and divide by 4 ohm load= 1296 watts...... now with a 13v supply 13 x3=39+,39-=78v x 78v=6084/4=1521
1521-1296= 225 watts difference by maintaining 1 volt higher)(keep in mind your 4 ohm speaker has an impedance curve that is much higher then 4 ohms at most frequencies so real power is much lower)
The way caps have helped in most cars is that the alternator now has another load. This load now lowers the average operating voltage of the cars electrical system example:
Before system- car running nothing else on 14.4v
Add system- system down 14.2v- when bass CD is pumping- 12.4
Now your electrical system is varying between 12.4 and 14.4v---- a 2 volt swing
Now add in a cap or two and the system now charges at 13.4v
Now your system will still dip close to the same 12.4v, but the high is now only 13.4= a 1 volt swing
Now your headlights dim half as much because there is only half the swing in voltage.
Now if you put a second battery in the back (more storage) the operating voltage will drop even more, lets say 13 volts (now you are barely charging the batteries without upgrading your alternator) By adding the battery in the back, you no longer are loosing voltage along the wire from the front battery. Also you have a lot of storage (2 batteries) so when you bass it up the power is coming mostly from the batteries and the alternators job is just to charge those batteries. So now when the amp hits a big rolling bass note the batteries will only drop to 12.6v
Now your swing is from 12.6-13v and .4 voltage drop on a headlight or dash light is next to nothing especially when compared to a 2v swing.
One other suggestion is to ALWAYS upgrade your ground wire at the battery. This is the least expensive way to make a huge difference in light dimming. There are a lot of cars that use a 8 or 6 gauge ground to the body (remember when you grounded your amp?) This cannot support the current return of the headlights and a 1000watt amp. Remember you may have a dedicated 4 gauge lead to the amp, but when that current returns to the battery it shares that ground with all the other components in the car that are grounded to the body.
All of the numbers in this post were submitted to show a point and do not actually reflect a single test environment. They only are used to help visualize what is happening to your cars electrical system when you go crank your bass up all the way and cruise down the street. Hope this has helped.........
all to do with physics etc... but if your brain can take the strain have a look here for a detailed explanation, its a long post but bear with it and all will be explained: