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What Should I Do If My Lights Dim to the Bass? Capacitors, Batteries, and More

Previously: How To: Size Your Audio System To Your Electrical System

Last week I showed a method to estimate how many watts your vehicle’s charging system can reliably power for your car audio upgrades. Now, for a variety of reasons we can over tax the charging system, most commonly with a combination of multi-thousand watt amplifiers and bass-heavy music on the factory original alternator and wiring. In this article I will lay out your options and give recommendations as to what to do.

“Stiffening” Capacitors

Massive Audio 4 Farad Capacitor
Massive Audio 4 Farad Capacitor

I want to jump right into the #1 “bandaid” go-to over-hyped product in car audio, the capacitor. This is a hotly debated subject, and there is a place for these products in the industry, but a lot of companies take advantage of misinformation to increase sales. The reference reading material on this subject, which I would argue has become outdated due to changes in music from the Loudness Wars, is:

‘Stiffening Capacitors’ by Richard Clark and David Navone, formerly of Autosound 2000, inc.

When this paper was written in the 1990s, it was more common for the music we purchase to have a wide dynamic range, with big changes in loudness that make music exciting. Albums became louder and louder, with less dynamic range, as producers strove to make recordings more radio friendly. When an entire song sounds loud the work our amplifiers do doesn’t change much. We want a fast discharging capacitor for our amplifier to provide stable voltage when the music reaches a sudden BIG change in loudness.

When our alternator can’t keep up, and the voltage sags(lights dimming), that capacitor needs to recharge. Agreed?

How can the capacitor recharge if the music is always loud?

Bigger Alternator

A big capacitor simply becomes another drain on the alternator, which is the last thing we want when our big audio system isn’t getting powered properly. Upgrading the alternator with a high current model should be a top priority. You want to look at the idle capacity as well as peak capacity. A 250 amp alternator that only puts out 100 amps at idle isn’t much of an upgrade, so pay attention to that idle rating. There are many reputable alternator manufacturers to choose from.

Bigger Battery / Additional Battery

I could write an entire article just about batteries. Please view this excellent video by Maxxsonics, USA. This is packed with a lot of information about batteries and what they do in your car.

The Big 3

Updated 1-29-2013

Previously this section talked about the common “Big 3” upgrade involving the installation of a new, larger, fused cable installed between the alternator and the battery’s positive terminal, and larger ground cables installed between the negative battery terminal and the frame and between the engine and the frame. I’ve learned of a different way to handle this that’s based on more accurate knowledge. The video below, filmed by Matt Borgardt of and the Backyardinstallers YouTube channel, talks about the Big 2.

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Barry Schanz

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