Introduction: DIY Portable Bluetooth Speaker 30W, BT4.0, Passive Radiators

Hey everybody! So in this tutorial I'm going to show you exactly how I built this (true) 30W RMS portable bluetooth speaker! Parts for this speaker can be obtained pretty easily and cheaply, and there will be links provided to everything needed. Everything in this project was built using only hand tools, meaning that anyone can build this project from home with ease. First off, here are some specs and features:

  • Bluetooth 4.0 with function keys
  • Real 30W RMS
  • 20 hour battery life
  • 18v power supply
  • 4 48mm Bose drivers
  • 1 5" Passive Radiator
  • Notifications LED

In this tutorial I won't go into a lot of detail about explaining how different parts work. I have already published a tutorial over here that explains different parts' functions in greater detail. I'd recommend reading both tutorials to really get the hang of it all :)

Step 1: Parts List

Step 2: Tools Needed:

You don't need any complicated tools for this build.

Useful Hand Tools:

  • Hacksaw
  • Files
  • Sandpaper
  • Snips
  • Scissors
  • Knives

Useful Power Tools/Electric Tools:

  • Drill
  • Soldering Iron
  • Hot Glue Gun
  • Multimeter

Step 3: Making the Enclosure

In this build we will reusing an old lunch box or other container. It's important to measure the dimensions of all your parts and make sure that they'll all comfortably fit in your container. It's also important to use a material thick enough so that the enclosure doesn't flex from the air pressure from the speakers. If you're using plastic, I would recommend you use plastic at least 2.5 mm thick. It's good to choose a box that will comfortably fit in your hand, and will also be able to stand independently.

In my case, I used a lunchbox. I had to cut the top down 5 cm. If you need to cut down your box, make sure you leave a few mm of extra space at the front so that your front panel wont be flush with the box. You need the extra space for adding a front speaker cloth (more on that later on). I cut the box down using a hacksaw blade. After you get your box down to the right size, we then need to drill holes for buttons, LED, charging and power switch. Use a needle file and a small drill bit to get the holes perfectly neat.

Next up, we need to sand down the outer and inner surfaces of the box. This makes the box a little more rough so that paint and glue will stick to it easier. Make sure to sand down all branding on the back of the box too to give it a more authentic look. Now that our box is ready, its time to work on the front panel.

Step 4: Making the Front Panel

On my speaker, the front panel is built out of 3 mm perspex. Perspex is great as its easy to work with and can be cut with a table saw. If you plan on cutting it with power tools, bare in mind that a tool with a rougher blade is better than tool with a finer blade. Finer blades may melt through the plastic rather than cut through it.

Mark out the size of your panel by laying it underneath your box, and trace a line around it. Then remove 2-3 mm depending on the thickness of your box.

Before cutting out the panel lay out all your parts and double check that everything fits. Next up mark it out and cut! I used a hole saw to drill out the driver holes, and then I cut out the passive radiator hole by drilling loads of small holes around the perimeter, and then filing them out to remove the centre piece. Be careful with your drill bit while drilling the holes, it can get quite hot!

Step 5: Preparing the Bluetooth Module and Amp

To fit everything into the enclosure, we're going to do a small bit of editing to the amp which will allow us to mount our Bluetooth module directly on to free PCB space on the amp. To do so we're going to unsolder the 2 rca inputs for the amp. We will solder cables directly on to the board instead. This frees up some space. In its place, we're going to put a small square of breadboard (copper side faced down), slightly raised off the board using hot glue, to prevent shorts.

Before mounting the Bluetooth module, we will solder on all the cables we need first. I have labelled all the connections in one of the photos above^. If your bluetooth module is in quite a cramped place where there won't be a good connection, you can add some length to the antenna by soldering a wire on to it (see the images for where to solder it^). To keep all the cables neatly together, I used little rings of heat shrink tubing around several cables.

Step 6: Building the 4S Battery Pack

This is the most dangerous part of the build. Lithium Ion batteries can be dangerous when mistreated, especially when you are dealing with multiple batteries. If you're new to DIY battery powered projects, I would recommend familiarising yourself with them first before undertaking projects like these.

First we need to connect all the batteries in series (ie. positive connected to negative). We'll connect them together by soldering a wire from one battery terminal to the other. You will also need another wire branching off from that wire to leave loose for connecting to the battery protection circuit board later on. Solder doesn't directly stick to the metal on 18650 batteries, so to make it stick, we will scratch the surface of the battery using a scribe and some sandpaper. Use a cloth to remove the metal dust afterwards instead of your fingers. The oils on your fingers can make the it more difficult to get a good contact to the metal. Now that its rougher, you should be able to solder on to the batteries more easily. Check out this guy's tutorial on it, he goes into the procedure a little bit more in depth.

Now that our batteries are all connected, we will tape them together into one handy compact battery pack. After that it's time to add the battery protection circuit. It will require battery positive and negative, as well as a wire coming from each of the cells. Battery protection circuits are important in order to keep the battery healthy and safe. After soldering up the protection circuit, you can also tape it in with the battery pack.

Lastly we will connect the switch and the charging port. Make sure not to connect the wires the wrong way around on the charging jack!! Always do tests with a multimeter first!

Step 7: Adding in the Voltage Step Up/Step Down Conveters

Now that our battery is all connected and protected, its time to add our voltage converters. We need a higher voltage for the amp, and a lower voltage for the Bluetooth Module. For the Amp, we will use a boost step up module, and for the Bluetooth module we will use a buck step down module. Be sure to set the voltages before connecting the amp/bluetooth module! Connect the inputs, and then use a small screwdriver to adjust the metal screw to change to voltage (see photo above for screw location^). You can monitor the voltage using a multimeter. For the Bluetooth module 5v is ideal, and for the amp 18v is ideal.

Your Bluetooth module should come with a 10V 470uF capacitor. Once you have set the voltage, add the capacitor across the positive and negative output of the step down converter. You don't need to add any capacitors to the step up module, as the amp already has capacitors built on to the board.

Now that we have the converters sorted, we will connect up the wires and mount them on a piece of breadboard, along with the amp and Bluetooth module. This keeps everything nicely together and adds a little bit of structural rigidity.

Now everything should be working! Try plugging in the charger, turning it on/off etc. Connect up the wires from the amp to the speakers and give it a listen to make sure everything's working OK. If it is, then we will continue on to by painting the box and front panel, and install our electronics.

Step 8: Finishing the Box

We're going to now spray paint the box and front panel. I decided to go with grey for the box, as I could then liven it up with a brightly coloured grille on the front. I used Montana Gold spray paint as well as a clear coat spray paint on top. Spray thin light layers in 5 minute intervals (depending on your type of paint) and wipe the surface in between sprays, until you have a solid coloured box. Then finish it off with several clear coats.

For the front I decided to use red paint. The colour of this panel really doesn't matter because there will be speaker cloth on top of it, but I wanted to paint it in some colour so that it would no longer be transparent. That way light leaks from the LEDs inside won't be visible.

Don't paint the inside of the enclosure! I did this first time round, and it just peals off when you have parts glued to it. You're best off leaving the surface unfinished.

Step 9: Adding the Electronics

Now that the box and front panel are complete, its time to add the components! Rest the box on a soft material so it doesn't get scratched, and add in all the parts. When adding in the buttons and switches, make sure you glue it very well so that no air can leave or enter the enclosure through the holes. Hot glue is great for sealing holes. I went quite a bit overboard with hot glue on this project as you can probably see, you don't have to go to such extremes as I did :)

You may also want to add some extra glue bridging sides together to add some structural rigidity to the enclosure. You want it to be as solid and stiff as possible.

When mounting the speakers and passive radiators, I used 2 piece epoxy, followed by hot glue to make sure that it's 100% sealed. As you've probably noticed, there are 4 drivers but only 2 channels, that's because each channel gets 2 drivers in series. Each driver is 4 Ohms, which means that each channel is 8 ohms.

When everything is all glued in place, solder wires from the speakers to the amp, and the slot the front panel into the enclosure. Test the speaker on final time before glueing on the front. To glue on the front, run a line of hot glue around the gap created between the front panel and the rest of the enclosure. Make sure that the glue doesn't reach above 1.5mm from the top of the enclosure, as we need that space clear for mounting the speaker cloth/grille.

Step 10: Adding the Speaker Cloth

To finish things off, we're going to add speaker cloth to the front. The 'speaker cloth' is actually just a piece of fabric from an old t-shirt. To keep it in place we're going to need some metal mesh glued in behind it. It needs to be clear enough for plenty of sound to pass through, but the holes shouldn't be too big either or else the pattern of the holes will come through the cloth. Add a small line of glue along the inner side of the metal and fold the fabric over it. Repeat for all 4 sides.

Now lastly to glue the panel on, we'll just add a few dabs of hot glue to the speaker panel and slot on the cloth panel and we're done!

Step 11: Final Thoughts

Overall I think this is a great speaker. By using a pre made enclosure (lunch box) you save time and internal space. The shape also looks very professionally done and people often ask me about how on earth I made those perfect curves! It's also a very practical speaker. It fits great in the hand and can resist water quite well compared to some of my other creations.

In terms of sound quality, I think its quite good. It has an insane power output of 30 watts, and the passive radiator really helps extend the lower frequencies. On the other hand, the bass often isn't boomy enough for my liking. An equaliser on your phone helps greatly with this issue. Playing around with different sized lunch boxes would change the sound significantly, so I may have a few more shots at it at a later stage.

If you have any questions, or would like to see some of my more recent designs and keep up to date on the latest Instructable tutorials, you can follow me here on my Facebook design page:

I'm selling lots of exotic speaker parts and passive radiators over on Etsy if you're interested:

If you've made anything else similar, I'd love to see it, post below! :D

Step 12: What I'm Working on Now

Just finishing off this speaker at the moment. Making a clear perspex cover for the front with holes in it as well as finishing off the clear coat on top of the wood. Don't be fooled by the crazy amount of speakers on it, its actually just as small as the blue speaker in this Instructable!

If you'd like to see more of this speaker, and be informed when the Instructable goes up, be sure to visit the Facebook page,

Thanks for reading, see you shortly! :D