Capacitor Guide

Guide To Car Audio Capacitors

If you’re a budding car audio aficionado, you’ve probably heard the term 'capacitor' pop up in various car audio forums, and on some sites. If you are wondering whether your car audio setup might be a good candidate for the addition of a car capacitor, it’s important to understand what a capacitor actually is and what it’s used for. 

Such an understanding will be crucial in determining whether your car audio system would benefit from the installation of such a device in your car, at all.

But before we begin, it's important to note that there are numerous types of capacitors that come in varying shapes and sizes, with different features and specifications. To get a deeper comprehension of car audio capacitors, let’s take a deeper look into what a capacitor actually does.

What Is A Capacitor?


​A capacitor is essentially a passive electronic device that stores electrical power. Some people refer to is as a cap, stiffening cap or power cap.  Aside from storing energy, a capacitor admits and discharges this energy whenever necessary. Since it can perform all these processes lightning fast, capacitors are widely used to buffer or filter abrupt changes in the voltage of your car's electrical circuitry, helping to smoothout the resulting signal.

How Does It Work?

​A car audio capacitor stores huge amounts of electrical power that is in turn delivered to other power-demanding components when necessary. The capacitors extremely low internal resistance gives it a huge advantage over your conventional lead-acid battery.

This unique property allows it to deliver vast amounts of power rapidly. It produces current much faster than a car’s ordinary charging system.  Most car audio amplifiers have huge current demands, depending on the music playing through the amplifier.

​Current is typically needed in very short busts that occur during the transient peaks such as the bass.  In case the amplifier tries to fetch this current directly from the vehicle’s electrical system, it may cause a significant drop in voltage. This voltage drop is known as "sag".  The level of the drop largely depends on the wire’s resistance from the battery (the source of electrical energy) to the amplifier.

​In this respect, a car audio capacitor provides a better, more efficient source of energy than the traditional lead acid battery in two ways.  Firstly, caps are usually placed nearer to the operating amplifier than conventional batteries.  Therefore, assuming all other parameters are equal, the voltage drop will consequently be lower in capacitors because of the shorter distance.

Secondly, your amplifier will prefer drawing it's current from the car’s battery and alternator, than drawing it from the charging system. But, the battery has a huge internal resistance that’s much higher than the capacitor’s. This large internal resistance makes the battery an inefficient source for providing vast quantities of immediate current.

​A capacitor can be likened to a small tank with a big hose. On the other hand, a battery can be envisioned as a huge tank with a tiny hose.  Integrating a capacitor to your car audio system ensures that large bursts of current are delivered during the music’s transient period. The capacitor can then recharge during those non-peak segments of the music.

​Can A Capacitor Benefit You?

​A combination of factors will determine the extent to which a capacitor will help you. These include your car make and model, the current draw of your audio amplifiers, the type of music you listen to, and your listening habits.

If your vehicle’s electrical system has a large reserve capacity (for instance, a huge battery and alternator), you’ll enjoy less benefits compared to a car that has an average charging system. If you possess a huge amplifier with a tremendously large current draw, you’ll definitely need to upgrade to a car audio capacitor. However, smaller systems still may not benefit significantly from this kind of upgrade.

Furthermore, if you typically only listen to the radio, you’re rarely going to experience huge transient peaks within your system. On the other hand, if you love listening to bass-heavy music, a car audio cap will greatly benefit you. Music that has extremely large peaks and dynamic ranges, such as classical music, will demand larger current draws.  Here, a stiffening cap can have a significantly positive impact.

Ultimately, if you desire optimum performance from your system, get a car audio capacitor. A good cap will allow you crank up the volume to the maximum without undermining energy supply to other critical components.

How To Know Whether You Need A Car Audio Capacitor

​If you notice your headlights constantly dimming, your system may be experiencing severe power problems - and the solution to dimming headlights is usually straightforward: get an appropriate capacitor.

But, although a capacitor typically helps, it’s not guaranteed to cure your car troubles entirely. There’s only so much that a capacitor can do. If your headlights dim only when your car is idle, a capacitor may help. Stiffening caps supply rapid jolts of power to the amplifier, helping to prevent your vehicle’s lights from dimming whenever heavy bass notes are played.

However, to truly determine whether you need a stiffening cap or not, check whether your car experiences persistent problems such as dimming lights. If not, then the added expense of buying a capacitor isn’t worth it. The only surefire way to know if your car will benefit from a capacitor is to try one and observe the results.

Since most car audio shops won’t allow you to test their stiffening capacitors, if you can, borrow one from a friend.  Ensure you observe all the recommended safety rules when installing and uninstalling capacitors. For instance, the battery’s negative terminal should be disconnected.

capacitor wiring

If your car continues to have dimming lights after installing the capacitor, you may either be suffering from an inadequate charging system or a defective charging system. In this case, it may be worth getting a qualified mechanic to check your car’s electrical system.

​What Capacitor Size Will Fit Me?

​A generally accepted rule is to inject 1 farad of capacitance into each 1000 watt system RMS power. However, there’s no harm in using capacitors with larger values.  More benefits may result from using around 2 or 3 Farads of capacitance per each 1000 watts RMS.