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How to Get loud Bass from Your Harley

 

The Quest for Harley Bass

Quick Overview

  • Choose the right woofers
  • Choose the best mounting configuration
  • Use the correct crossover settings
  • Use the correct equalization settings
  • Get the phase correct 

 Once you choose the right woofers and get them properly mounted in the bags, there are some EQ and crossover tricks that will allow you squeeze out a ton of acoustic power and bass response while at the same time protect your woofers from melting down. In fact, you can get them to play so loud that they can be heard loud and clear on the highway and will blow people away in the parking lot. Attempting to get a lot of bass without a good sound processor though is not recommended at all. 

Some of this is a long read. So I have broken this article up into sections. You can read the first part of each section if you want and then go back over what you didn't get if you need to. The important part is that you know the basics. I go into length on some points for those who are interested. 

The Quest for Bass - Know What You Don't Know.

There are some things that must be understood about bass in a Harley application before you even start thinking about what equipment you are going to use. In this article I will explain several tricks and tips that will allow you to select the proper equipment for spectacular results. I will also cover how to properly set the system up. You can have all of the best equipment, but without proper setup you really can not expect your system to be very impressive. There are very good options for big bass on a Harley but none of them are anything like what you will see in a car or boat system.

Before you go down the path of bass you have two choices. Get to know and understand all of the information in this article or buy all of your parts from a shop that already knows this stuff. 

About Your Installer

You should know going into this that your typical bike shop or car audio shop will not likely be educated about Harley bass, so don't be surprised. 

 

Rule #1 

Subwoofers... Don't do it!

Subwoofer

Know what you are looking at and don't listen to anyone who has not successfully built a system that you have heard in person. It's a fact; many, many people have tried to get bass from a Harley and most all of them have failed. Doing what worked in your car will not work here!

Subwoofers are generally a bad idea for a lot of reasons. A traditional car or marine subwoofer is designed to only work within a very limited band of frequencies. This small range of frequencies is also the same range as your pipes, the wind, and traffic. Unless your bass is substantially louder than all of this, you will not be able to hear it muchless be impressed by the volume. Too often we see someone fall in love with a car audio subwoofer and in turn endup on a doomed quest to make that subwoofer perform in their bike system. There is a lot more to why a traditional subwoofer is a very bad idea that will be covered throughout this article but the point here is, a huge iron magnet and a heavy moving mass (cone) will not perform well on a bike. 

But Don't You Want a Subwoofer for Bass?

Diamond HXM Marine Subwoofers Harley Road Glide

Not really. A much better way of going about it in the Harley application is to use a wade band pro audio type woofer. Actually I should say "woofers". A single large diameter woofer is not a good idea here. 

In the above pic I used two 10" Diamond Audio HXM free air marine subwoofers. This turned out to be an impressive parking lot system and the best sounding Harley subwoofer system I have ever heard. In retrospect though, four 8" woofers put out a lot more volume, play as low, requires only one amp, weighs a small fraction, and leaves a lot more bag room. 

Why Pro Audio and What Does Pro Audio Mean Anyway?

Pro Audio Woofers

Pro audio refers to a speaker design typically found in professional musician applications like guitar amps and live concert speakers. These speaker systems are not designed anything like your home audio speakers or your car audio speaker systems. These types of speakers are much more efficient than other types of speakers. They simply put out a lot more sound for every watt that they are fed. This is done by keeping the moving mass (cone & suspension) weight to a minimum and by keeping the cone movement much more tightly regulated mechanically. This is why pro audio speakers a lot of times have a paper cone and a progressive suspension surround (accordion looking surround). Additionally these speakers have a much higher thermal limit. This means that these speakers are designed to run at full boogie for 8 hours without thermal failure. Car and home speakers are not designed like this because you are so much closer to the speakers than in a concert situation. On a Harley we need all of the output possible. So even though we are right on top of the speakers we still need them to endure extreme volume levels for extended periods of time. 

Not all pro audio woofers are the same. A lot of people refer to pro audio woofers as "mids". This can be true but for the most part this has become common because people are selecting the wrong speaker. 

The Wrong Pro Audio Mid If You Want Bass.

  • Resonant frequency is too high (Fs). Should be close to 50 hz. 
  • Resonant magnitude is too low (Qts)  Should be .4 or higher. 

The Fs is the resonant frequency point where the woofer starts to ring and lose control. The higher the Qts the lower that the woofer will be able to effectively play at or below the Fs but the more it will ring. Fact of the matter is that in a Harley application we want the woofer to ring a bit on the bottom end.  

Magnets!

Neo Magnet

This part throws most people. We have all been taught over the years and the generations that bigger iron magnets are always better. This is the equivalent of shopping for a fast car based on the tire size. There is such a thing as an under sized magnet but what is important to know is that there is also more than one type of magnet out there. The big heavy iron magnets that are so prevalent in the speaker market are popular for two reasons. 

  1. Iron magnets are cheap. Low cost is real good for manufacturers 
  2. Iron magnets look more impressive. 

A much more premium magnet type is neodymium. Neo magnets are made of a refined metal that oxidises rapidly in open air. Consequently it is typically coated in chrome or some other type of coating to keep it from oxidizing. This makes it quite a bit more expensive compared to an iron magnet. 

In a Harley application neo magnet speakers have a few other advantages over iron magnet speakers. 

  1. Keeps the center of gravity on the bike lower by not adding a bunch of weight up high. For lid speakers you won't need a forklift to open your bags. 
  2. Leaves more storage space due to the small size.
  3. Packs a much bigger punch due to better magnetic flux density.

Focused magnetic flux is common in high end speakers even with iron magnets, and not really a factor that engineers can do much about in low cost speakers. It kind of is, what it is. The small physical size of neo magnets make them inherently easier to arrange in such a way that the magnetic energy is better focused on the voice coil. 

Wider range of frequencies

As I stated earlier, traditional subwoofers are very limited to a small range of frequencies. In a Harley application it is very important to cover as wide of a range of frequencies as possible. Its not just the low bass that gets sucked up and dissipated by the wind, traffic, and your pipes. All of the sound gets gobbled up. So the more speaker cone area you have contributing to output, the better your system will be at overcoming these acoustic obstacles. 

Speaker Size

I often get the question, " are 10' speakers better or 8". The answer is, the more cone surface area you have the better. a 10 has more cone area than an 8 but two 8s have quite a bit more cone surface area than one 10. 

My favorite setup is two 8" speakers in each bag for a total of 4 woofers. 

Way outside the Scope of This Article!

Then there are other factors of speaker design that simply fall way outside the scope of this particular article that involve how various electromechanical characteristics of a particular speaker design interact with each other and the application. 

What We Know Now

  • Traditional Subwoofers Are a Real Bad Idea
  • Neo Magnets Are Best
  • Lightweight Cones Get Us More Output

Setup Crossover, EQ, & Phase

In order to explain how to set up I am going to use my favorite woofers as an example with very specific parameters. These setting will not work for all speakers. 

My Speaker Choice - Diamond Audio HXM8 / Cerwin Vega SM8

Harley Woofers for Big Bass

These two speakers are both based on the same design, come from the same factory, and are nearly identical in performance. Although these speakers are not truly pro audio speakers (they are motor sports/marine) they do have all of the important characteristics of a pro audio speaker. 

  • Neo magnet
  • Very high efficiency
  • Wide frequency band
  • Wide dispersion 
  • High Qts
  • Low (enough) resonant frequency

Crossover

High pass at 50 hz with a 48 db per octave crossover slope. We want to cut off all information below 50 hz so that all energy can be focused on the speakers playable range and nothing is wasted on excessive cone movement. Settings on a Rockford Fosgate DSR1 processor should look like this. 

High pass

EQ

In the advanced EQ section the EQ is a parametric type. This means that I can not only select a frequency band to increase or decrease, but I can also change how much effect that adjustment will have on surrounding frequency bands by lowering the Q value attached to that band. See below.  

 EQ1

Above you can see that I set band #7 to a frequency of 83hz with a Q of .970 and boosted it by 6 db. This creates a huge bump across a lot of the bass frequency range with a focus on 83 hz. 

EQ2

Next I selected band # 16 and set it for 630 hz with a Q of .620 (even wider), and I cut by 7.5 db. This is because the boost I put at 83 hz also affects the lower midrange too much, making the vocals sound a bit overbearing. The net result is a rollercoaster looking EQ curve. But i am not done yet. 

In the next pic I overlayed the high pass crossover plot with the EQ plot so that we can see what the net result of both will get us. 

High Pass and EQ Overlay

 Notice that the audio information on the vary low end of the frequency spectrum is cut off sharply. This does two things for us. 

  1. Saves our speaker from self destruction. 
  2. Allows more energy to be focused on the bass region that we can hear.

It is very important to cut out all low frequency information that falls below the speakers abilities. 

The end result here is a system that will play very aggressively down to 40 hz. This is low enough to cover 90% of all the low frequency information in most any recording.  

 

 

 

 

 

 

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