What You Need Before Adding a Subwoofer to Your Harley

When you step up to adding a real subwoofer to a Harley Davidson audio system you need to have a few things in place so that the subwoofer system will perform properly. If you are not already familiar with what you should expect and how to get the most out of your Harley subwoofer system, please read this article.

Harley Sound Systems Are Different Than Other Sound Systems.

Subwoofers in a Harley sound system are at a distinct disadvantage. They have to play louder than the surrounding environment (wind, pipes, helmet, traffic), and they do not have a big steel structure to reflect the bass back at the listener like a car has. Therefore the output is dramatically reduced as compared to a car, home, or boat. But we have several tricks up our sleeve that allow us to get higher volume levels and puts some protection in place for the subwoofers as well.   

Don't Miss a Step!

When setting up a subwoofer in a Harley system you can not afford to skip any steps or cut any corners. Or chances are that you will be left with disappointing result. 

Most Common Mistakes

  • Not having a good DSP
  • Not understanding how to align phase using a DSP
  • Setting the crossovers up like a car, home, or boat
  • Not selecting the proper lid speakers
  • Not setting gains correctly
  • Adding bass boost


A subwoofer is a link in an audio system. That link is only as strong as the weakest link in the audio chain. We do not recommend ever adding a subwoofer to a motorcycle without first adding a digital sound processor. Once you get to the level of adding a subwoofer to a motorcycle sound system you need to have other components in the sound system that are conducive to that high level of performance. And a DSP is definitely one of those components. 

A DSP is an equalizer, crossover, and phase alignment device all wrapped up in one. With today's amazingly powerful and capable digital devices it no longer makes any sense to make just an EQ like car audio systems used to have back in the 80's. It costs nothing extra to include crossovers and phase alignment settings. And in Harley systems we need those extra tools.  

Why Do I Need a DSP?

A Digital Sound Processor is the only reasonable way to control the final outcome of a large scale Harley audio system. Once you add a subwoofer to a Harley audio system you officially have a large scale audio system regardless of how many other speaker you do or don't have. If you do not make all of the critical amplifier, DSP, and crossover settings properly, you can not expect to have a great outcome. 

These settings include phase relationship of the subwoofer properly in relation to the other speakers in the system. This can only be properly done using a DSP and is not the same thing as wiring the subwoofers in proper phase. That is a different thing entirely. 

There Is a Bad Side Effect of Dsp and Amplifier Crossovers

And here is how you get around it. Most people are unaware that crossovers and equalizers can invert the audio signal as it passes through them. This goes for crossovers and equalizers that are built into the radio, DSP, and your amplifiers. By the time the signal gets to your speakers there is no telling how many times the signal has been flip flopped. And each set of speakers will be potentially different. 

So now you probably have multiple speakers that are working out of sync with other speakers in your system. If you could slow down time and look at the speaker cone movements you would see that while some speakers are moving outwards other speakers are moving inwards. So they defeat each other. And it's devastating to bass reproduction. 

Even though this signal flip flopping happens, the benefits of crossovers and equalizers are so great that it wouldn't make any sense not to use them. They are an very necessary evil.  

A Quick and Easy Work Around

Good DSP units like the Rockford Fosgate DSR1 have a speaker channel inverting feature built into them. So at a tap of an icon on your smartphone you can invert or re-invert any single speaker in your system. 

The result in sound for better or worse will be evident right away. So you don't need any special test equipment and you don't need to take anything on your bike apart. 

Always Make Changes in Pairs

If the audio signal going to your right speaker is inverted by the crossovers and EQ the same inversion is also happening on your left speaker. This is because the signal path is exactly the same. So we are not looking for speaker signal that is inverted left when compared to right. We are looking for speaker signal that is inverted when comparing the front speakers to the rear speakers or the lid speakers compared the subwoofers. So Always make your changes in pairs. Flip the signal going to both left and right speakers one pair at a time and then listen for a better or worse sound. You will hear it right away. 

Subwoofer Testing

The subwoofer channels on a DSR1 have left and right sides tied together. So you can not invert just the left or just the right sub. But that's okay, because you want to invert left and right at the same time anyway. If you do need to invert just a left or right sub you will need to physically flip the positive and negative connections around directly at the speaker. You should not need to do this unless you accidently wired one of the subs wrong. If you are experiencing poor bass response even after trying multiple combinations of inverting speaker signal to all of the other speakers, then you should assume that you did get one of the subs wired backwards and try reversing one sub. If you have 4 subs you should be mindful of the possibility that you may or may not have wired more than one sub backwards. So you are better off just disconnecting the subs from the connection point at the amplifier and visually testing direction using a 9 volt battery.   

The Quick and Dirty Explanation of Phase Alignment

Speakers move their cones back and forth in order to create sound waves. When you have multiple speakers, all speakers have to be wired the same so that they all collectively create one sound wave at the same time. If one or more speakers are not wired correctly, that speaker will be working in opposition to all of the other speakers and devastate the sound. Particularly the bass portion of the sound.   

What You Probably Already Know & What You Probably Don't Know

If you have ever worked with speakers before you are probably already familiar with wiring the speakers correctly as described above. But what you probably don't know is that even with all of the speakers wired properly there is still a very good chance that some of those speakers are moving in the opposite direction as what you wired them for.  

Well How the Hell Does That Happen?

It gets messed up at the signal level. Usually at the amplifier. Often times at the DSP as well. When audio signal is passed through a device like an amplifier with on board crossovers or a DSP, the audio signal often times gets inverted. It's impossible to predict where and when in the audio chain this will happen. 

Why It Happens

The audio signal gets delayed as it passes through crossovers and equalizers. This is an unwanted side effect of crossovers and equalizers.