Today we'll try and build a Bluetooth speaker! Visually it looks aesthetically pleasing with a lovely wooden front and a concrete outer shell. This concrete is not only for the looks, but it also helps with the audio quality, as the sound produced by the speaker is very solid due to the lack of resonance. It’s all powered by power cells on the top, these can just pop out and get recharged whenever required. A variety of fantastic techniques will be used for this project, so sit back and enjoy!
- Things you need:
Dayton Audio ND65 speaker drivers
30w Mini Amplifier
DC-DC Isolating Converter
Step down voltage converter
Battery Bank Tubes
The most effort required for this project will go into building the frame for moulding the concrete. So we will make our frame by using a set of wooden pieces, a link is provided for the templates of the pieces.
Then print the template onto paper and stick them to a board and cut around carefully using a coping saw, pieces can be glued together and sealed with a mix of PVA and water. With that down, we need a sheet of acetate and wrap it around the inside of the larger frame with double-sided tape and the outside of the smaller frame. This will allow the concrete to slide off it once it's set.
The smaller frame can now have a piece of acetate stuck to the top after which you can screw it to the remaining cut out, sliding this inside the larger frame, leave a hole on the side to make a gap in the concrete for the power cells. It should look something like this:
Time for the concreting, for every 2 spoons of sand add one spoon of cement. Add some water bit by bit until it reaches a nice and thick consistency. After this, you can spoon this into the mould we made and let it dry up to 48 hours.
Time to work on the electronics. Pop off the case of the Bluetooth receiver, to wire up the audio output we need a short length of screen audio cable which can be soldered to the audio output pads and the other end can go to a dual-gang potentiometer which will act as volume control and can be wired up like so:
The additional wire from the potentiometer can be hooked up to the amplifier’s input tabs, now we can add the power wires to the tabs vcc/gnd. We want the Bluetooth module to power up by these same wires so simple expose a section and solder them to the input tabs of a voltage step down the board. Fit a dc to dc isolating converters between voltage step down the board and the Bluetooth module as shown here:
We need a front panel to mount everything, I made mine from 2 layers out of which one included a fibreboard that included some cutouts for the wires. It also matches the internal dimensions of the concrete.
Start mounting the components on the panel, thread the potentiometer into the wood and the other components can sensibly be grouped around it and glued down in place.
Now it’s time to mount the speaker drivers by screwing them onto the panel and solder them to the amplifier’s speaker outputs.
Add a volume knob to finish everything up, now you can test this by hooking up the power wires to a power source of anywhere between 12-24 volts.
Now it’s time to carefully de-mould our concrete structure, and sand down any imperfections. Paint the structure with some acrylic paint.
Now that the concrete shell is all done, we can use a piece of cut fibreboard with some ribs on the inside to mount the front panel.
We need to work on the battery system, for this, you need a set of 5 to 6 lithium-ion batteries with protection circuits and put these inside some empty battery bank tubes. Don’t forget to remove the electronics and replace them with xt60 connectors instead. Now some short pieces of pipe can be inserted and glued into a fibreboard for the batteries to slide into. Wire all the batteries in series, for this you’ll need some xt60 sockets and solder them together and glue them in the bottom
of the tubes.
Securely glue this unit inside the concrete, last thing on the list is to solder the battery pack wires to the amplifier circuit after which you can stick a piece of sponge around the inner edge to seal things when the front panel is pushed in, screw the panel tightly down and insert the batteries in the power cell.
And your speaker is ready to jam music!
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