To put this into context, I took my first Loopy’s tubing trip long before waterproof Bluetooth speakers were something you could just go pick up at your local Circuit City. For the average rivergoer, a tranquil float down the serene Chippewa River on a beautiful sunny day is already pretty hard to beat. But what kind of engineer would I be if I didn’t seize the opportunity to enhance such a natural experience with a piece of cobbled together tech designed for the sole purpose of blasting out the fattest bangers of 2005?
What started out as a dumpster dived boombox implanted into a chest cooler blaring out distorted audio from a burned “River Mix” CD has evolved over the years into the latest incarnation seen above. Affectionately known as “DJ Big Gulp”, the name was inspired by an off-the-shelf solution for a watertight chassis, the Igloo 1/2 Gallon Sport Jug With Hooks – better known to some as a “Big Gulp.”
Big Gulps, huh?
A Big Gulp may not seem like an obvious first choice for a river-floating speaker enclosure, but it actually works great for a couple reasons. The first one should be obvious – it’s watertight. Less obvious but arguably more valuable, the main opening just so happens to perfectly fit a standard 5-1/4″ car speaker. A bit of foam weather stripping is all that’s needed to hold the woofer in snugly. Devoid of thirst quenching electrolytes, the empty reservoir serves as a resonance cavity, providing a much needed bass boost. Finally, the handle comes in, well, handy for lugging the rig around on dry land.
The Guts
DJ Big Gulp is powered by a 12V SLA Battery Definitely not the most energy dense option out there, but it fits neatly inside (just barely) and provides more than enough runtime for an entire 2 – 3 hour river float. I considered upgrading to lithium ion a few times over the years, but abandoned it for one reason or another.
The audio system consists of a single Pioneer 5-1/4″ Speaker driven by a Bluetooth Amplifier Board. There are a ton of these fairly cheap amplifier boards out there. I’ve had success with a few of them and chose this particular one because it can run directly off 12V, packs a decent punch in terms of output power, and its terminal strip makes for a more compact wiring configuration than barrel connectors.
The beats are streamed from a phone that hangs around my neck in a waterproof bag. As phones have become water resistant over the years, protecting the phone itself has become less necessary. But until they make floatable phones, the bag is still a handy way of keeping it from doing any unsanctioned diving. And if you’re extra clumsy or paranoid, slapping big chuck of leftover pool noodle on the lanyard isn’t a bad idea either.
Tubular Tetris
Creating an amplifier board enclosure that would fit inside the Big Gulp alongside the bulky battery and speaker turned out to be trickier than I expected. I started with a nice boxy-shaped box but ended up needing to hug those tall caps in the middle to make it fit, resulting in the camel-humped monstrosity you see here. Making a crude model of the entire assembly helped me figure out the right fit without burning through too many spools of filament in the process.
Of course, you could just chuck the amplifier board in there bare and pray for the best. But historically, DJ Big Gulp’s reputation for remaining vertical throughout the float has been spotty at best. The ghosts of fried amplifiers past would strongly discourage this approach. Surprisingly however, the woofer itself has survived numerous dunks without any trouble, despite lacking any level of marine rating.
Inverted pendulum
A stock Big Gulp will float just fine on its own – the problem is the orientation. It naturally wants to lay on its side. Hang a heavy speaker magnet on top and it’s propensity for self sabotage rises exponentially. My first answer to this was to use a wheelbarrow innertube for floatation. This worked well while the Big Gulp was more or less unperturbed, but any significant disturbance usually resulted in an (often fatal) capsize.
To increase stability, I devised this “pool noodle pontoon” approach. The noodles are wrapped around a PVC pipe frame, which is connected to a 3D-printed harness that the Big Gulp slides into. Although still not perfect, it has had a much better track record on the open seas. The fact that it doesn’t require inflation or make my whole car reek like a sleezy discount tire store during transport are also pluses. The only real downside is the added bulkiness of the frame.
Cheat code
Don’t have the time or desire to mess around building the guts? In a pinch, you can just chuck an off-the-shelf bluetooth speaker inside and no one will be the wiser. My JBL Charge 5 fits nicely and has come in handy when I forgot to charge the SLA battery.
Materials
- All of the files for the 3D printed parts can be downloaded from Printables or Thingiverse
- Main body
- Igloo Sport 1/2 Gallon Jug With Hooks
- Pioneer 5-1/4″ Speaker
- 12V SLA Battery
- Marine weather stripping
- Amplifier Enclosure
- Bluetooth Amplifier Board
- 4 Pan head screw 8-32 3/8″
- 4 Pan head screw M3 x 0.5 mm Thread, 5 mm Long
- 4 Heat-Set Inserts for Plastic, Brass, 8-32 Thread Size, 1/4″ Installed Length
- 4 Heat-Set Inserts for Plastic, Brass, M3 x 0.5 mm, 4.3 mm Installed Length
- 3D-printed “DAMGOO Enclosure Cover”
- 3D-printed “DAMGOO Enclosure Base”
- Wire
- Spade connectors
- Velcro strips (to hold battery)
- 3D-printed “DJ Big Gulp Lid”
- Flotation
- Roughly 10′ of 1/2″ Schedule 40 CPVC pipe (0.62″ OD to fit into bracket)
- 8 45° elbows
- 4 Tee fittings
- Pool noodle
- 3D-printed “DJ Big Gulp 4 Leg Bracket”
Printing Tips
- 0.2 mm layer height and 15% infill should be fine
- No supports needed except for “DAMGOO Enclosure Cover” – print it with the hump touching the build plate
Assembly Tips
- Cut the mounting tabs off the speaker – I used a Dremel
- Attach the marine weather stripping about ¾” from the top of the opening, just above where the contour of the inside changes
- The PVC legs connect to the bracket at a 35° angle – only one combination of leg length and base perimeter will satisfy this requirement. I’d suggest dry fitting first and trimming if necessary. My legs are about 10″ long.
- The main body isn’t permanently attached to the flotation frame. You might need to apply a little duct tape to the main body so that there’s enough friction to keep it from slipping out when you pick it up by the handle
For vids of the build process, audio tests, and previous dead ends, head over to Instagram.
