Introduction: Portable Bluetooth 2.1 Boombox

About: Nice to meet you! I'm Donny from Lithuania and I have a passion for designing aesthetic, yet durable and practical projects. Check my YouTube channel for more! ▶

Hi everyone!

In this build I decided to come up with a portable Bluetooth boombox that would have a rechargeable battery and great performance. This speaker is based on Paul Carmody's Isetta speaker build which I have slightly remodeled to accommodate a hefty battery and all the electronics inside to make it portable.

Make sure to check my YouTube video of this build first!

Full build plans, wiring diagram, parts list and much more included down below, so let's get moving with the build!

Step 1: Parts, Plans, Materials and Tools

As I always I am trying my best to make this build simple for you by providing free plans, wiring diagram, crossover diagram by Paul Carmody and the parts and tools list. Feel free to download the plans (available metric and imperial) and the wiring diagrams and make sure to zoom in for a better view!

I have simplified the build plans to reduce the number of parts used in the build. It also makes the speaker look much cleaner!


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Step 2: Let the Build Begin!

To begin the speaker build I bought a few square meters of 12mm (1/2") MDF board which I cut up according to the plans. I used a table saw for best results but you could also use a jig saw or a circular saw with a guide to cut out the panels. Whichever tool you use make sure to use it with your own caution.

Working with MDF makes a lot of dust which is not healthy to breathe in so make sure you not only wear eye protection, but a breathing mask as well.

Once I got the panels cut out exactly to the dimensions on the plans, I marked the centers for each speaker hole.

Step 3: Cutting Out the Speaker Holes

I then took a 127mm (5") and a 76mm (3") hole saw with a drill bit attached to drill out the holes for the woofer and the full range speakers making sure to drill halfway through on each side to avoid tearout.

I also used a 38mm (1.5") hole saw to drill out the hole for the subwoofer port. It may still be too small for the port that you will be using but a bit of sanding will make sure that the port stays firmly in place.

Step 4: Glue Up

(Avoid my mistake! - Predrill the holes from the inside of the top panel for the speaker handle threaded inserts. I forgot to do it so once I glued the enclosure it was too late and difficult to have the threaded inserts installed from the inside of the speaker.)

A truly rewarding step of the build when you can finally see the speaker taking shape! To glue the enclosure I used simple wood glue, making sure to scrape the excess glue off the edges until it has fully dried. Keep in mind that you will have to use a square to make sure the edges are square to each other before the glue cures. Once I got the front panel glued in and gave the glue some time to cure, I glued the long and thin panel support pieces, simply cut straight from the MDF sheet. I made sure to glue them in approximately 10mm from the edge to make it easier to align them with the back panel. More on that in the next step.

Step 5: Inserting the Back Panel

To insert the back panel correctly, I made sure to glue in the panel support pieces a little closer to the edge than they should be. Before the glue dries I inserted the back panel resting it on the support pieces and gave it a few knocks with a hammer to align it with the corners making it sit flush to the support pieces and the outer edge. Once you have the back panel aligned, make sure to remove it clean off any excess glue that may have spread out by moving them when using the hammer.

Step 6: The Control Panel

To make the control panel for the amplifier controls download and print the last page in the plans I have uploaded in the second step. Double check the dimensions on the printed sheet and adjust the scale if neede. Then cut out a piece of thin plywood or a sheet of plastic according to the size of the drawing and glue the template on. After that I used a center punch to make marks for the holes that will have to be drilled out. Start with a small drill and move your way up through the sizes to avoid tearout of the panel. A step drill bit is a great tool for this purpose to quickly enlarge the hole.

Once the holes have been drilled out, remove the template and give the panel a light sanding. I also used a sander to give the edges a smoother feel. After that a few layers of matte spray lacquer gave it the protection it needed.

Step 7: More Drilling

To make the square cut out of the control panel I drilled four holes in each corner using a forstner bit and used a jig saw to cut along the line. A few strokes with a file will make the edges straight and even.

I also drilled the mounting holes for the speaker handle (which was my mistake not to install the threaded inserts before gluing the enclosure).

Step 8: Smooth!

Next I followed up with a random orbital sander to knock down any rough edges and dried up glue to make the surface nice and smooth for painting later.

I also marked the corners for the rubber feet and drilled them out.

Step 9: Rounding the Edges

To round off the edges I used a router with a round over bit to give the edges a nice radius all around. Make sure to use a dust collection system because this process will generate a lot of nasty dust!

Step 10: The Back Panel

Firstly I marked the holes for the screws in the back panel 6mm (1/4") from the edge. Using a center punch I marked the holes and drilled them out. I also cut out a rectangle for the battery capacity indicator and two more holes for the charging jack and the push button.

I then placed the back panel in place and while holding it firmly I marked the holes with a center punch for the screws that will hold the back panel in place. I then took the panel out and drilled the holes all the way through the support pieces using a smaller drill bit than the one for the back panel.

Step 11: Preparing for Paint

For this step I lightly roughened the surfaces with a sanding sponge. I then used long screws and screwed them in place of the rubber feet to use them as stands when painting.

To seal the MDF for painting I mixed a 50/50 batch of Titebond III wood glue and water to make a sealer which I have applied to all the surfaces that will be painted.

Step 12: Subwoofer Port

This was a first-timer for me. Making my own subwoofer port out of PVC tubing! I thought I would fail badly at this but it turned out to be quite simple. Since the subwoofer port for the speaker needs to around 250mm (10") in length, I decided to make the port flared on both ends so I used a 38mm (1.5") PVC pipe and a connector and made flares on both of them. Always start with a longer pipe in order to trim it to size once it is flared.

To begin the flaring process I quickly built a port template using the MDF cutouts from the subwoofer port. I glued them on top of another making a cylinder which I later covered with some putty to make sure the pipe fits in with no wobble. I also contoured a radius around the bottom of the template to make the flare.

I then took a heat gun and placed it on the bottom of template and turned on the hot air. Turning the pipe and slightly pushing down ensures that the pipe heats up evenly and starts to soften allowing us to push it around the radius creating a flare. Once the desired flare has been reached, the heat can be turned off and a few seconds allowed for the pipe to cool down and solidify again leaving us with a nice custom port!

Step 13: Time for Some Paint!

Now that the sealant has fully dried I used a sanding sponge once again to rough up the surfaces for better paint adhesion. Before painting I wiped down the enclosure with a solvent to remove any oils, residue and dust from the surface.

A light layer of primer was applied at first following up with a mist of black paint, resulting in a "smoky" finish.

Step 14: Electronics

Make sure to check my wiring diagram and the crossover diagram in the plans above!

For the battery I used a 6 battery pack from 18650 cells using a BMS board to make sure they stay balanced. To assemble the battery pack I used 12 cell holders and then soldered the batteries to the BMS board. I know that soldering 18650 cells is not the safest option, but making sure to apply the heat for a few seconds to melt the solder will keep them safe and usable. I used a piece of adhesive foam on top of the cells to insulate it from the BMS board. A few strips of Kapton tape will make sure the contacts are insulated as well.

To build the crossovers I made small 'table' for each of them in order to make it look cleaner even though no one will probably ever see it, haha! Follow the crossover diagram posted above to assemble the crossover.

As you can see I also glued the panels to enclose the full range speakers.

Step 15: Last Steps!

Now follows the final assembly of the speaker! These small steps include some straight-forward procedures as seen in the video, such as:

  • Placing the woofer and marking the screw holes
  • Predrilling the screw holes
  • Placing adhesive foam tape around edges to make the speaker airtight
  • Installing the amplifier to the control panel
  • Gluing in the subwoofer port
  • Installing the battery capacity indicator, push button and the charging jack
  • Screwing down the control panel
  • Screwing in the back panel
  • Installing the drivers
  • Mounting the rubber feet
  • Installing the handle and amplifier knobs

Once these assembly steps have been completed, we have a functional Bluetooth 2.1 boombox ready to blast some tunes!

Step 16: Final Thoughts

Charging time of the speaker depends on the capacity of the cells that you will be using. It takes around 4 hours to fully charge this speaker using some second hand 18650 cells with a decreased capacity. As you can also see, by the press of the button we can see the capacity of the battery left.

Personally I am very happy how this speaker turned out. It has loads of power and sounds really nice and clean.

I hope you learned something new following me through this tutorial and perhaps I inspired you to build one yourself!

See you on the next build!

- Donny

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