What We Learned From Building Australia's Loudest Harley

Custom Build · Lessons Learned

Australia's loudest Harley audio build is not a show bike. It is a 2017 Road Glide Special that Alex still rides, and since we finished it the bike has lived a real life on the road. That is what separates this article from the two before it. Part 1 covered what the system is and Part 2 covered how it was built. This one is the honest version: what building and living with a 159.9 dB Road Glide has actually taught us, the decisions we would make again without hesitation, the ones we would change, and where the bike goes next.

It is worth being clear about what this bike is, because 159.9 dB invites the wrong assumption. A pure SPL machine exists to score a number on a meter, once, in a controlled lane. This one had to do that and then ride home. It runs eight speakers, two subwoofers and a full DSP tune, and it has to play cleanly at conversation volume on a Sunday morning as well as flat out at a bike night. Building for both is a completely different engineering problem to building for one, and almost every lesson below comes out of that tension.

Most build content stops at the finished photo. The useful part starts after it, once the panels are back on and the bike has to earn its place on real roads.

Would We Build the Same System Today?

Very similar, but not identical. The shape stays the same: eight speakers and two subwoofers. What changes is how the system is split and how it is driven. We would separate the front stage further between mid-bass, midrange and highs by moving to component speakers instead of coaxials, and drive the tweeters actively rather than through passive crossovers, for far more control over the top end. That means more amplifier channels and more processing, so the DSP architecture would grow too: either one larger processor or multiple processors, depending on the final channel layout. The amplifier choices would shift as well. And where this bike runs Hertz front to back, the next one would most likely be built around Cicada, with a mix of brands where it earns its place.

What We'd Engineer Differently

One decision stands out, and we already know what it is: we would port and brace the saddlebags from the start. At the time we discussed it and chose not to, because Alex was already planning to move to a set of extended Dirty Bird bags, and it made no sense to do that fabrication twice. The call was reasonable then. But the subs have been asking for more air ever since, so porting and bracing is firmly back on the cards, sooner rather than later.

That regret is worth sitting with, because it is where the serious end of this scene has already moved. Overseas, speaker count alone is no longer enough at the top of the competition classes. The difference increasingly comes down to acoustic loading: enclosure volume, port tuning, panel resonance and how the structure behaves when a subwoofer is trying to flex it. Bolting another pair of drivers into a panel that moves is the easy version of the job. Turning that panel into a proper enclosure first is the version that changes what you actually hear. If you take one lesson from this article, take that one. The enclosure is not the job you do after the speakers; it is the job that decides what the speakers are capable of.

The second change is the processor. This bike runs a Hertz S8, which has served the build well, but the Cicada DSP412PRO did not exist when we built it. It is physically smaller than the S8, which would have made cable management and device placement behind the fairing noticeably easier, and it would have given us more flexibility in the tune. If you are weighing those two processors up for your own build, we compared them directly in Hertz S8 DSP vs DSP412PRO vs HKI Mini DSP.

The third is the front stage, and this one is personal taste. There is nothing wrong with the Hertz SX 165 NEO coaxials in the fairing, and the SV 165.1 SPL midrange in the lower pods does exactly what we asked of it. I simply like my music a little brighter than that front stage delivers, and a set of components up front, separate midrange and tweeters driven actively, would have added the brightness and air I prefer.

What We'd Do With No Budget Ceiling

Ask Alex and me the same question and you'll get two completely different answers. For Alex it is a whole other ballgame. He would go the full competition route, the direction the headline American show baggers have taken: the chassis rebuilt around the audio, speakers filling every panel that will hold one, custom bodywork built to house drivers rather than luggage, and a bike whose job is to win a class. Think The Powerhouse, The Toxic Teal and The Sith Bagger, or the competition Road Glides out of Baggers Audio and Certified Audio. Those bikes are the reason the scene keeps moving forward, and Alex would happily point at any of them.

Mine stays a road bike. Same ambition, different brief: spend everything on output and control, but the result still has to start on a cold morning, ride four hours to a show and carry a bag when you get there. That constraint is the whole difference between the two answers, and it is the one I would keep.

Before the list: this is not a final build sheet or a promise of what Alex's bike will receive. It is simply the system I would design today if packaging and budget were removed from the conversation.

Up front, I would use a Cicada DSP412PRO to run the fairing and lower-front stages fully active. Each position would use separate mid-bass drivers and tweeters, taken from a pair of 14CXK65.2 component kits with the supplied passive crossovers left out of circuit, so the processor does all the filtering. An FLX1400.4 would power the mids and an FLX700.4 would power the tweeters. The tweeter channels would be gain and limiter controlled through the DSP, giving us far more control than a passive crossover while keeping each driver properly protected. The speaker amps and the processor all tuck up under the front fairing, out of sight.

At the rear, the bike would use the 14HDXBAG10LID8 extended bag system, with its 10-inch cutouts in the bag bodies and 8-inch cutouts in the lids. A second FLX1400.4 would run four Cicada CM8.2X 8-inch speakers at 2 ohms, one per amplifier channel: two in the saddlebag lids and two in custom mounts in the Tour-Pak. I would keep the original bags as well, so there is still somewhere to pack for a weekend away, and every bag speaker would run on quick disconnects so it lifts out in seconds.

For bass, an FLX2500.1 mounted in the Tour-Pak would drive a pair of Cicada CMB10.S4 4 ohm drivers, one in each saddlebag and wired as a 2 ohm pair. Although Cicada classifies them as mid-bass drivers rather than true subwoofers, they comfortably reach into subwoofer territory while delivering the punch and efficiency that work exceptionally well in Harley saddlebag enclosures. The DSP would provide the high-pass filtering, output limiting and gain control needed to use the amplifier's headroom without asking the drivers to absorb uncontrolled power. The bags themselves would be glassed, structurally braced, properly ported and sealed against unwanted air leaks. And a Dube Custom bass knob on the amp, because bass you can reach for is bass you actually use.

Power would change too. Instead of one large battery I would run three Braille G30H batteries, two in the Tour-Pak and one in the factory location. They carry the current a system like this demands, but their much smaller size makes them far easier to mount and frees up real space in the build. The trade-off is play time: you give up some of the marathon run time the big LiFePO4 delivers.

What Six Months of Riding Taught Us

This is the part a spec sheet cannot give you. A system is a set of decisions, and only time on the road tells you which ones were right. Here is what the bike has taught us since.

The decision we would never change, and the biggest surprise

Both come back to the same component: the 100Ah LiFePO4 auxiliary battery. It is a monster, in physical size and in capacity, and it earns every bit of the space it takes. Part of the original brief was long demo time, hours of playback with the engine off at shows, bike nights and club events. Music draws power unevenly, so run time is genuinely hard to calculate, and our best estimate was around four and a half hours. The longest single session we sat down and logged was five hours of playback with more than half the battery still showing, which is the figure quoted in Part 1. Across mixed use since then, including periods at demonstration volume and periods at comfortable listening levels, Alex has seen close to seven hours from the auxiliary battery. That is the decision we would never change, and the one that has outperformed every expectation we set for it. If you are working out what your own bike can support, start with whether your charging system can handle an audio upgrade.

What looked good on paper

The trickiest part of the entire build was the remote turn-on. Every amplifier and the DSP run on a dedicated circuit from the LiFePO4, while the SoundStream HDHU.V2 head unit runs off the factory power. The isolator inside the battery charger stopped the remote turn-on signal from getting through, so the amps simply would not wake up. Solving it meant building a relay system to trigger the turn-on properly. On paper it was a single wire. In practice it was the biggest headache of the build.

What real riding has stressed

Across its first six months of regular use, the system has been remarkably solid. And Alex genuinely rides this bike; it has not spent those six months sitting in a workshop or travelling on a trailer. The only failure has been a single XT60 connector on the clutch-side saddlebag speaker, which we repaired. Beyond that there has been no water ingress and no damage. For a system this size, living on a bike that gets ridden hard, that is a strong record.

The maintenance reality

Two things, and both are minor. First, a retune: the system was deliberately tuned down for the first few months while everything bedded in, then brought back up once it had settled. Second, and the one thing Alex has to remember, is charging the LiFePO4 before a big weekend away. When the system is cranked it draws more than the alternator puts back, so a full charge before you leave is the difference between all-day sound and a flat auxiliary battery.

What's Next for Alex's Road Glide

The system above is my blank-cheque thought experiment. Alex's confirmed next stage is different, and it starts with the bike itself.

On the chassis and styling side, the plan is a ground-up stance change. The bike still runs its standard suspension today, and that is the first thing to go: an American Suspension rake kit, then full front and rear air ride with an auto centre stand so the bike can still be stood upright cleanly when the suspension is aired out. An SMT 26 inch front wheel sits behind a wrap-around front guard, with Dirty Bird Concepts Street Sweeper audio bags and rear fender, plus a stretched tank and matching side covers pulling the whole body line long and low. Then a custom paint job as wild as the sound and the lines of the bike.

The audio is not standing still either. The next round is a bass-focused upgrade, and it starts with the porting and bracing we would have done on day one. The saddlebags get ported and braced to let the subs move real air, all unintended gaps sealed, the structure reinforced and appropriate sound treatment applied, and the subwoofers and their amplifier stepped up for more power and deeper extension. The current sealed enclosures did exactly what they were built to do, tight and controlled inside a standard bag volume. The Dirty Bird Street Sweeper rear end opens up airspace those standard bags never had, and that is what finally makes bracing, porting and bigger subs worth doing. Same bike, engineered one stage further.

We will document that build the same way we documented this one, in a Part 4. That one is a way off yet, closer to twelve months out, because a transformation on this scale takes time to do properly. When it is done, you will see it here first.

Our Advice for Anyone Planning a Big Harley Audio Build

Plan the power and the processing before you fall in love with the speakers. Almost everyone starts with drivers and amplifiers, because that is the exciting part. But the two things that decide whether a big system is reliable or a constant headache are the power supply feeding it and the DSP controlling it. This build is the proof: the auxiliary battery is the decision we would never change, and the remote turn-on tied to that power design was the hardest problem to solve. Get the power and the processing designed first, and the speaker choices become the easy part.

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