Trailer mountable stereo system

Hey yah, so sometimes you want to listen to music with a dozen friends but can’t agree on who gets to haul all the gear. For those times, why not have a sound system that can easily drop into a bike trailer bed?

I started with some plywood and drew circles to mark cutouts for speakers:

01 - plywood

Painted it black, then built up the sides with 2x4s:

02 - side

and made a box:

03 - box framed

Once that was done, the next step was to build a simple base out of plywood. An internal divider was installed to separate the subwoofer enclosure from the midrange speaker enclosure:

04- box platform internal bracing

The subwoofer enclosure is sized for a reasonably flat bass frequency profile. Math!

The midrange speakers installed easily enough:

05 - side speakers

The subwoofer was straightforward to mount as well:

06 - subwoofer mounted

I used a closet flange and a short length of PVC, painted blue, to make a port. The port will give this subwoofer enclosure a louder bass sound in this relatively small enclosure:

07 - port installed

There are two amplifiers in this system. One is a T-class stereo amplifier for the midrange speakers. That’s installed on the inside of the box to keep it away from weather — this drop-in stereo system is designed to work even in rain. The speakers and the second D-class monoblock subwoofer amplifier are all marine grade equipment. Here are both amps installed:

08 - sub amp

The final step was to devise a mounting system for the marine battery. This was easily the most time consuming aspect of this project. I used steel bedframe (sandblasted and painted yellow), flat steel bar, inner tubes, threaded rod and some fasteners:

09 - battery mounting

The inside of the subwoofer enclosure section was packed with polyfill (pillow stuffing), which keeps the size of the enclosure small without compromising the bass frequency response. A simple electrical/audio bus box was added to tie all the electrical components together. Here’s the completed trailer mountable stereo system:

10 - completed radiobox trailer

After the inaugural ride — where it performed admirably — I ended up adding a roll cage around the electrical box to protect it from damage, as well as a tall safety flag for improved visibility.

2 Comments so far

  1. chris on March 5th, 2014

    what kind of battery will last if im making one on a bike with two EVs

  2. h4ckw0r7h on March 5th, 2014

    It depends on the average load of your audio system and how long you want the battery to last. What I would do is power it up using a bench power supply, crank it to the volume you’ll be playing music at, and then measure the current draw with an analog multimeter. Watch the multimeter and make an educated observation about how much current it’s drawing on average. Then size your battery appropriately for how long you want the music to play.

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