In this article: We unbox and review Infinity's Kappa Perfect Harley Davidson speakers and walk through all of their key features that make them a premium, high performance choice for your Harley.

The Kappa and Kappa Perfect series speakers are among Infinity’s highest performing speakers. We’ve seen them used in competition automotive systems for some time now, so I was excited about the Kappa Perfect motorcycle series when I first saw them. In this review, I’m going to unbox a set of Infinity's 600X motorcycle speakers, give you a closeup of them and walk you through some of their key features.

Unbox & First Impressions

The Kappa Perfect motorcycle speakers are designed specifically for the motorcycle application and even more specifically, they’re designed to be a replacement or upgrade for the factory speakers that are on 2014 and newer Harleys. There’s two sizes in this lineup right now:

  1. The 600X, which is a 6 ½ inch 2-way setup. These are a good choice for your Tour Pack and lowers. They also come with multiple sets of grilles that are great for adapting/replacing your Road Glide and Street Glide fronts. I'll show you these further in the review.
  2. Then there's the 900X, which is the 6×9 inch version. I did not have one of these in person, but they're great for your Tour Pack as well, and come with a cut-kit and templates that will allow you to modify your factory speaker lids with ease. It'll also save you a chunk of money that you would otherwise spend to buy one-off lids, custom paint them, etc. The 900X model shares almost all of the same technology that I’m going to talk through with this 6 ½ model though so this review is still very relevant for those interested in the 900X model.

When you pull the speakers our of the box for the first time and take a close look, you'll really get a sense of their beautiful design. Their suspended tweeters are stunning, and use an infinity symbol as the suspension arms. The woven cone material sort of glimmers in the light, which I’ll get into a little more further in the review. Just a gorgeous set of speakers. They pass the eyeball test!

What's in the Box

Infinity Kappa Perfect 600X all of the components that are in the box
A look at all of the components, grilles and hardware that comes in the box of the 600X

There's a lot in the box, so I pulled everything from the packaging and lined it up on my bench to show the variety of components that the 600X comes with. Here's a list of everything you see in the picture above.

  • (2) 2-way speakers
  • (2) 16″ Lengths of wire with in-line crossovers
  • (2) Surface mount tweeter housings
  • (2) Tweeter opening covers
  • (2) Street Glide grilles
  • (2) Road Glide grilles
  • (2) Tour-Pak grilles
  • (1) Tweeter removal tool
  • (8) 5/8″ Screws
  • (4) 5/8″ Flat head screws
  • Installation instructions
  • Template on box
  • (3) Infinity logo badges

Sound & Performance Features

Let's dig into some of the individual components of these speakers and detail out the key features that Infinity incorporated to make them great for your Harley or motorcycle.

Woofer Cone & Surround

Infinity Kappa Perfect 600X basalt cone
Closeup of the 600X Basalt woven cone

Starting with the speaker cone – they're beautiful but their design isn't just for show. I’ve seen manufacturers adhere a woven material onto the cones just to make them look like they have a carbon fiber or other expensive woven material. But when I flipped them around, the cone was actually a standard polypropylene material. This isn't the case with the 600X and 900X.

The Kappa Perfect series use a woven basalt fiber for the cone. Basalt is a volcanic rock, and somehow or another engineers discovered that it has properties that make it a great material for speaker cones when mixed with other materials and woven. Focal's PS 165 FXE uses Flax, while other manufacturers use carbon fiber, pressed paper and so on. Infinity uses basalt, which must have better rigidity, durability, dampening and weight properties than traditional paper or polypropylene cones. It's good to see proprietary, woven materials like this in most cases because 1) it's more expensive to manufacture which indicates it has better performance properties and 2) these types of materials typically go through extensive testing prior to use and in most cases result in a superior performing speaker because of it.

The 600X cone also uses another proprietary Infinity feature called Plus One technology. When combined with a high roll rubber surround, it helps these speakers have a greater surface area and response which is good for lower, bassy frequencies. 6 1/2″ speakers aren't exactly designed for bass, so by incorporating features like Plus One and this high-roll rubber surround, Infinity was clearly prioritizing lower frequencies. These features are relevant on a motorcycle because when you install a speaker out in the open, bass doesn't carry as well as it would inside an enclosed vehicle. So the speaker has to either work harder to produce those lower frequencies or the design must improve how efficiently it produces those lower frequencies in order for you to hear them well outdoors.

Here's a few other images of the cone and surround.

Neodymium Magnet

When you pickup these speakers and turn it to it's back you'll notice two things:

  1. It's pretty light
  2. The magnet is pretty small

Traditionally you’d like to see bigger, heavier magnets. Large magnets indicated (in most cases) a more powerful and better performing speaker. But technology is improving, and by using more modern (and expensive) materials like Neodymium you can really get a significant amount of efficiency and power with a smaller, lighter design. And that’s what you see here. Weight is a characteristic that's more important for a motorcycle than it is in the door panel of a car. These speakers are light weight for that reason, but don't necessarily sacrifice performance and size to shave ounces.

Removable, Suspended Tweeter Design

The 600X and 900X speakers have a suspended tweeter design. This means there's no pole that comes out of the center of the cone to fix the tweeter to. Suspended tweeters give the speaker cone a larger surface area like a traditional component speaker. A larger cone is good for lower frequencies and carrying a little more bass. I mentioned this earlier, but this is especially important for the motorcycle application where bass doesn't carry as well outdoors as it does inside a car.

As for the tweeter, Infinity uses a polyphenylene sulfide material for the dome. If you feel it, it’s a soft(er) material. Not necessarily a hard-dome like aluminum or titanium but not necessarily a soft dome either. Harder tweeter dome materials give you a brighter sounding speaker. The highs are brighter and carry further, which is good for an outdoor use case like this. So by using a polyphenylene sulfide material, it's kind of in-between a metal hard dome tweeter and a softer fabric dome tweeter and gives you a good blend between bright and soft high frequencies.

But what's even more unique about the tweeter design on the 600X and 900X is that they're removable. Infinity designed a tweeter housing that you can untwist the tweeter from the speaker itself, and mount it separately. It's a really cool design. They provide you with a tool to uninstall and re-install the tweeter, along with a tweeter kit that will allow you to mount and wire the tweeter independently from the larger speaker. Here's some picture of how it works.

I think for 90% of use cases, especially if you're looking for a simple speaker swap on your Harley, you'll probably keep the tweeters as they come – installed on the speaker. But for the 10% of you who would like to do some custom work and mount the tweeter separate, Infinity thought of it and provide you with the tools to make it happen.

Bi-Amping & Crossovers

One of the cool features worth calling out when looking at the back side of the speaker, specifically the terminals is their ability to bi-amp the speakers with ease. If you're a more advanced audiophile and are interested in getting the most out of these speakers, bi-amping will allow you to use dedicated channels from your amplifier(s) for both the tweeter and the woofer separately. Then, you can manage the frequencies directly from your amp or DSP instead of using the active passovers provided by Infinity. This requires a bit of knowledge and work and I wouldn't recommend it unless you're familiar with the process and tuning.

Alternatively, if you're a weekend DIYer and would prefer simplicity, you can simply plug in the provided passovers to your Harley's existing speaker wire and let the crossovers handle the frequency ranges.

Motorcycle & Harley Specific Features

Performance features aside, I think there's two other key things to point out about this series of speakers that make it ideal for a Harley Davidson (and other motorcycles).


Starting with the grilles, Infinity provides three pairs of grilles that are designed specifically for Harleys. Road Glides, Street Glides and Tour Pack owners will benefit greatly from these grilles. They're designed to simplify the installation but will also add a little personalized touch to your Harley with the Infinity logo and grilles.

The 600X comes with a pair of standard round 6 ½” grilles which are good for your lowers or your Tour Pack. But they also provide Road Glide and Street Glide specific grilles that will fit in the factory front locations. They come with everything you need to just push or screw into the factory location – they’re sealed and have the clips as well.

IPX Rating

Choosing a speaker that will withstand the conditions on the road is important and shouldn't be overlooked. I wouldn't recommend using just any standard automotive speaker for your motorcycle. Rain, UV, moisture, heat, cold – these are all things that motorcycle speakers have to withstand.

Infinity's Kappa Perfect Motorcycle speakers are IPX5 rated. What that means is Infinity spent some additional time weather proofing them, and put them through a series of water tests done by an independent certifier. It might not sound like a big deal, but if you went through a rain storm with speakers that have a pressed paper cone, they wouldn't last the day. So knowing that the speaker materials will hold up to the weather on the road is really important.

Speaker Specs

Now that I've walked through some of the core features of the PS 165 FXE, here's a quick overview of the PS 165 FXE's performance specifications.

  • Size/Type: 6.5″ Coaxial Speaker
  • Impedance: 3-ohm
  • Power Handling: 75 watts RMS (225 watts peak)
  • Frequency response: 60-20,000 Hz
  • Sensitivity: 93 dB


I was impressed by the 600X from the moment I pulled them out of the box. Infinity blends a ton of their traditional high performance technology like Plus One with other technologies like basalt woven cones, Neodymium magnets and high-roll surrounds to produce a high performing speaker. And most importantly, it's suitable for the motorcycle application with its IPX5 rating.

The speaker looks phenomenal – I really love how Infinity incorporated the ‘infinity' sign into the speaker to suspend the tweeter. And they were also thinking very specifically about the Harley Davidson owners with the variety of custom grilles to help simplify your installation.

All in all, very satisfied with these speakers upon inspection and first look and can't wait to get them tested in a Harley. Stay tuned for that installation!