well... i have a 500/1 mono JL amp with 2 12W3s 4ohm

well im wodering if you all would recomend a capasitor...
my light dim slightly when loud... and... the rear light goes crazy, not sure if from low power to it....or is its just rattleing like hell and is just going in and out of connection well... just wondering... thx cory

EDIT: i have 4gauge wire on it...

 

Dimming lights are a sign that your alternator isn't producing enough current durring loud bass notes in the stereo. A capacitor is a band-aid for the real problem. It may or may not help in your situation. Go ahead and try at least a 1 farad capacitor and see if it helps. If not, your next step would be to get a high output alternator.

 

For most average, read: non SPL competition, individuals a capacitor will help the stereo perform better. It takes a lot of power to create the low frequency boom that so many people enjoy. I don't mean lots of watts, I mean lots of amps. Granted, during normal music play this current draw is only momentarily, but it happens frequently. Basically the amp has to reach all the way to the batter for the extra amperage that it needs. While the car is running, the alternator is what actually supplies this amperage and in some cases it cannot handle the additional load that the amp is placing on it during those short bursts. This is why your headlights dim during bass hits.

The capacitor acts as a go between for the amplifier. It sits in the power stream between the amp and the battery and when the amp needs a little extra juice, the capacitor feeds it to the amp. The cap the recharges itself from the battery. This charge/drain/recharge cycle typically happens EXTREMELY fast, so fast that you never realize that it's happening. The capacitor can be thought of as a mini-battery, that is designed to give all it's juice REALLY quickly so the amp doesn't have to get the extra juice from the battery.

The rule of thumb for capacitors is 1 farad per 1000 watts RMS of power in the car. I generally double that amount, so for your 500w amp, I would get a 1 farad cap. The 1 farad isn't twice the cost of a 1/2 farad, and it will leave you a little room for growth.

If you are competing in SPL competition, the capacitor can actually HURT you, because in most SPL comps you run a sine wave to make the amp push all the signal possible out to the subs, this will instantly drain the cap and because of the constant drain of the sine wave during measurement, the cap won't have time to recharge itself. This causes the amp AND the cap to BOTH place a drain on the battery.

LS1 RULZ is correct that a high output alternator will help and in the SPL competitor's case, it's almost always a requirement. But for most average people who don't compete, and just listen to music, the cap is an awesome first step. Even with an upgraded alternator, you'll still possibly get headlight drain, because it is harder for the amp to get all the power it needs from the battery in the front of the car, so it has to draw even more power. Getting the cap and placing it near the battery will assist more in the long run in my opinion.

You will likely notice an improvement in sound quality as well as loudness after installing a cap. This would be my first step, then an alternator.

Hope the info helps!

 

I agree with everything stated above except for this. It is common knowledge that the cap MUST go as close to the sub amp as possible to realize the benefits of the cap. Otherwise the long run of power cable to the back of the car and it's associated resistance will negate any benefit that the cap will provide. In a perfect world, an ideal power supply would have zero output impedance. Since this isn't possible in the real world it is critical to have the cap as close to the sub amp as possible to keep the power supply's output impedance as low as possible.

 

Ummm, aren't watts, amps and volts all interlocked, you know something like power (watts)=amps x volts....

 

Actually I meant to say that the cap should go closer to the amp and tripped over my own fingers...

And yes amps, watts, and volts are all interdependant on one another. I wanted to make sure that he didn't think I was trying to tell him to go buy a more powerful amp.

Sorry for the confusion.

 

The capacitor near the battery has got me thinking...

I don't think he would make a great deal and don't know if it would help that much, but. Would having a cap at both ends (amp, battery) would the help "flow" the current better?

Would it also give you less clipping distortion?

...LS1 RULZ?

 

There's no point in having a cap near the battery. Like I said above the resistance of the power cable will negate any benefit it might provide.

Using a cap has no effect on clipping. Once the amplifier has reached the limits of it's power rails thats all it can do. All the caps in the world won't change that. A cap is just there to provide an extra burst of current on loud bass notes. It doesn't raise the voltage on the rails.