When I have friends over for a BBQ or go camping, I like to have some music playing. In the past, I've used a Small Portable Speaker that I attached to a cooler. These small transducers work by transferring the sound waves into whatever surface they are connected to, essentially turning them into a speaker. Although it sounded decent, the battery life and volume was lacking. Recently, Gearbest.com contacted me and graciously sent me out an Audio Amplifier and Bluetooth adapter module -- perfect for this project. The Bluetooth adapter is completely optional, I just liked the idea of having the extra capability. I stopped at harbor freight and picked up a cheap enclosure and utilized my quadcopter batteries and charger for the power source. This was a super simple project and the outcome was exactly what I was looking for in a durable portable speaker option. Here's the final BOM:

LiPo Battery $16.70
Hard Case Enclosure $14.99
Marine Speakers $11.75
Audio Amplifier $14.55
Bluetooth Adapter Module $28.17 (OPTIONAL)

Step 1: Layout and Cutting Holes

The first step of the layout is to take off the potentiometer knobs, nuts, and screws of the front. I used the faceplate to trace an outline for the mounting hole. The hole should be smaller than the faceplate to allow the electronics to fit through but also leave enough material around the edges to drill the 4 mounting screw holes. Next I used calipers to measure the diameter of the speakers to figure out the size of hole I needed. I traced these onto a piece of cardboard using a compass. I traced both the faceplate and speaker holes using a pencil, removed the foam from the lid, drilled a small pilot hole, and used a coping saw to cut them out. This was by far the most time consuming part of the whole build. An electric jig saw may have made things go faster but I was concerned with how thin the material was. After the holes were cut I used some hand files to smooth out the cuts.

Step 2: Electronics

The Bluetooth Adapter needs a 5V supply. The amp uses a 12V supply but I suspected there was a 5V line in there somewhere. I removed the four corner screws, pulled out the circuit board, powered it up, and probed around until I found a 5V supply. Next, a hole was drilled in the amplifier's PCB and metal housing, the Bluetooth adapters power connector was trimmed, and the wires were soldered up and fished through the PCB/housing. This step can be skipped if Bluetooth functionality is not desired. To run the amp off of an audio cable, I close the enclosure with only one latch and route the audio cable through the other side with the unlocked latch. This closes the enclosure but does not pinch the cable.

The amp was reassembled and mounted into the enclosure along with the speakers. I soldered up a power adapter using a X60 connector and a barrel plug I had one hand. If a power adapter connector is not available, a cable like this 2.1mmx5.5mm Splitter would be suitable. The battery was connected to the Amplifier, the Bluetooth Adapter was connected to the Amplifier input and power cord, and the two speakers were wired up.

This thing is surprisingly loud for its size and each battery lasts around 4 hours at high volume. The treble and bass adjustments on the front make it easy to tune and the mini remote is pretty handy as well.