New member
Username: Brett2387

Burlington, WI United States

Post Number: 6
Registered: Dec-04
Will I need to buy a capacitor for an Audiobahn HCT amplifier powering a ALUM12Q sub? If so, how many farads?

The sub has 1000 watt RMS and the amp will fully power the sub.

Bronze Member
Username: Terminatermule


Post Number: 32
Registered: Nov-04
Hi Brett

Its probably a good idea unless you have an awsome battery and cabling just as good. Remember, the cap can't magically make you charging system work better, so if you install the sub and amp and get dimming lights and a battery that is flat after heaps of time pounding the sub, you need a better alternator and battery and all cabling that goes with them pair. If your cool with the rest of the setup and only need a cap for short hits of heavy bass, then a 1 - 1.5 should do you. The rule of thumb AFAIK is 1 Farad cap per 1000 watts RMS.

Cheers Glenn

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 6042
Registered: Dec-03
Well let's see. First, I'll define what a capacitor is, how it works, and what it does. This is best done by the following webpage:

Now with that out of the way, I'll give my take on what a capacitor will or will not do for you.

A capacitor WILL:
-Stiffen voltage rails. If you experience very brief, momentary periods of high current demand that cause the electrical system to falter only at these rare, peak draw times, then a capacitor will supply the additional current needed (when bass hits) to keep your voltage rails stiff, and prevent damage to the car or audio equipment.
-Increase response times for musical accuracy by reducing delay caused by transient response times between current demands from the amplifier, and response to this by the electrical system. In other words, your subs will respond more quickly, because they don't have to wait for the alternator to supply additional current at the moment of demand. Amplifiers have to provide a very dynamic and quick response many times. A capacitor can assist in this if the rest of the charging system is up to par.

A capacitor will NOT:
-replace the need for a larger, high-output alternator and/or a deep-cycle battery or batteries.
If your electrical system is inadequate, the ONLY way to fix this, and again I repeat, the ONLY WAY to fix this, is to replace the alternator. This is the SOLE source of electrical current for your car when the motor is running.
When the motor is turned off, the battery then becomes your source of electricity.
When the battery is run down, and when the capacitor(s) is/are depleted, the alternator has to work even harder in order to supply current to the car, the audio system, and also to recharge the capacitor(s) (which deplete very quickly) as well as recharge the car's battery(ies).
So by adding a capacitor to try taking the place of a high-output alternator, you are actually causing more work for your alternator, and causing even more damage to that stock alternator.
-make your system magically sound 10 times better.

Many people believe that a capacitor adds NO real benefit to an audio system, and this is why you never see before and after demonstrations, or factory capacitor company vehicles at competition events.
A capacitor does have it's uses, but it is not a magical fix for a lacking electrical system.

To calculate the capacitance needed for your system, you will need to find the peak or max power ratings of your amplifiers, and add those together. This is the only time peak amplifier power ratings are even remotely useful, since a capacitor is only used to cover very brief peak demands, and not cover for the continuous amplifier demands.
Take the peak power total and figure 1 farad of capacitance for every 1000 watts of power.
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