Brent Walther

Portable Custom Boombox

Sunday, Aug 18, 2019

Tags: project, portable custom boombox, waterproof, bluetooth, marine, radiocooler

(a.k.a. radio cooler v2)

The custom radio cooler (and other prior art) I built in college has been dragged all over the place between tailgates, pool days, the beach, camping, and hunting trips. It is a complete workhorse optimized for battery life and durability at the cost of portability (the 100 Ah battery weighs a ton!). I decided I wanted to build something sleeker and more portable, so that’s what I did.

The first step was choosing some type of case. Coolers are pretty convenient because they’re easy to cut through and they can be fairly water resistant but they are also difficult to seal well. I began looking at electrical junction boxes (and I still think one could work quite well) but many had awkward dimensions and I wasn’t sure if drilling or cutting through them would work well. I finally settled on a latching plastic case meant for electrical components or firearms. It seals well and has a convenient handle already installed. It also was long enough to fit three speakers.

Empty case. The starting point of the portable boombox.
Empty case, all bottom foam removed.
Case with amplifier inside.
Amplifier sizing.

The case is quite spacious inside. I placed the amplifier in first to size it up but I definitely researched the dimensions of everything before purchasing.

Inside of case with speakers, amplifier, battery, and aluminum rails installed.
Installed speakers, aluminum rails cut, and battery mounting bracket is shown.
Outside of case after installing speakers.
Outside of case with speakers installed, along with a bunch of tools and hardware from the job.

I carefully measured and cut out holes for the speakers using a dremel tool. I used a tiny cutting wheel to get a rough shape first and then used one of the sanding heads to round them out. If I were to do it a second time, I would tape templates down from the start to get perfectly round holes. After cutting the holes, I installed the speakers using bolts and wing nuts as well as a bit of silicon sealant around the speaker beds.

The components on the inside are mounted via aluminum C-channel I found at Home Depot. It was inexpensive, reasonably strong, light weight, and shouldn’t rust if any moisture gets inside. The two T brackets ended up getting mounted behind the battery to C-channel two cross members. The battery is 12V/20Ah sealed unit I picked up on Amazon. The entire assembly is mounted to the case at 4 anchor points: 2 to the bottom of the battery and two at the place where the lower amplifier holes are.

Finished portable custom boombox front.
Finished boombox front w/ trickle charger.

The finished boombox looks quite nice from the front and uses a small trickle charger to charge up. It sits easily upright though I would love to have a way to also sit it on its side so the three speakers were stacked. The sound is very directional (somehow to my surprise) so it’s best placed facing the direction you want the sound to go. The volume of the case with all components installed seems close to the right size to get good speaker suspension – bass is loud and even shakes the lid some. I usually connect with bluetooth to my phone, and Spotify has an integrated equalizer (deep in the settings) I’ve used to fine tune.

The inside of the boombox is reasonably organized. The battery is strapped in place with paracord (as not to jar the battery as much if the boombox is knocked in to) and a switch is placed alongside the bluetooth receiver module. I highly recommend the JL Audio unit; I tried multiple cheaper ones and they all had terrible background noise. The little round piece attached to the battery is a small 2-port USB hub with screen that shows the battery voltage to give an approximate idea of charge level. I eventually uninstalled it because it drained the battery, and moved the bluetooth unit’s circuit to go through the switch, so it drawn nothing when off now.

Completed inside of portable custom boombox.
Finished and wired inside.
Finished portable custom boombox rear.
Finished boombox rear w/ trickle charger.

The rear only contains 4 mounting bolts which can be easily sealed with silicon caulking. The boombox is significantly more portable than the previous iteration and can be carried with one hand like a suit case.

Parts List

Here’s a non-exhaustive list of what I used for this build. Including hardware one of these can be built for around $350. It’s way louder than the all-in-one stereo units you can find at Costco or Sams Club.