Wireless Bluetooth Speaker in a Bowl

Who needs breakfast anyway? A bowl is perfectly suited as a Bluetooth speaker.

Designing a speaker from scratch can be daunting. Even if you know everything about electronics, the real power of a speaker is in the aesthetics. So why start from scratch? Just grab something that is beautiful by itself and make a bluetooth speaker. In this case we will use a bowl.

This is a list of items I used:

• three 3d prints from: thingiverse
• a 15.5cm wide round bowl with an advised depth of 6cm or more (for acoustic reasons) Blokker if you are in The Netherlands
• 20x20cm of speaker cloth
• two full-range 2 inch (53mm) speakers Aliexpress
• PAM8403 amplifier with volume knob Aliexpress
• 5v bluetooth module Aliexpress
• usb-c charger module Aliexpress
• step-up converter (I used the MT3608 from Aliexpress)
• 18650 3.7v battery (can be from any seller)
• 18650 battery holder Aliexpress

To create this project you need:

• 3d printer (or access to one) with a bed that is at least 155x155mm
• scissors
• spray glue (or other hobby-grade glue)
• hot glue
• soldering iron
• small flat screwdriver
• multimeter
• wires

Print the faceplate, ring and insert from the thingiverse site. I used a black PLA without supports or other help structures. The files are pretty simple. I choose black because my speaker cloth is also black and partly translucent. Keep this in mind when printing yours. The speaker cloth will show the PLA that is below it, so matching the colors is advisable.

To construct the faceplate we need to put the three 3D printed files together with the speaker cloth. To get a nice finish follow this step based guide:

1. make sure you have somebody who can help for one minute to lightly stretch out the cloth on a flat surface
2. glue the front of the faceplate with spray glue. Don't use to much because it can seep through the cloth and leaves ugly marks
3. press the faceplate with glue gently on the cloth (that is still being lightly stretched)
4. wait a minute to let the glue dry
5. put the ring over the cloth and pull the sides of the cloth tight so the sides of the faceplate also look nice
6. Cut the cloth to length around the ring and at the same time hot glue the ring and the cloth to the inner structure of the faceplate. This will ensure everything stays in place.
7. cut open the inner part of the cloth to make space for the insert for power and volume
8. Add some glue to the insert and gently push it in place.
9. Let it all dry a while.

We are going to solder the power stage of the speaker. There are three components needed and we need to dial in the step-up converter. Let's go!

1. Solder the 18650 battery holder, USB-C charger and step-up module like shown in the image above. While doing so, do NOT place the 18650 battery in the holder.
2. After you are done with the soldering, double check your wiring and then place the 18650 battery in the holder. The step-up module can step-up to a wide range of voltages and we need to set it at 5V.
3. place the multimeter at the 'OUT' part of the step-up converter and measure the current voltage (normally somewhere between 10 and 20 volt)
4. While keeping the multimeter on the output, turn the potentiometer on the module with a small flat screwdriver until the meter is between 4.8 and 5.1 volt.
5. To make sure the potentiometer will not change its value, use a dot of hot glue to secure it in its current position.
6. Remove the 18650 battery from the holder to create a safe situation for the next steps.

After we know for sure the powerstage is dialed in correctly we can feed the power to the amplifier and the bluetooth module. If you use the same bluetooth module as I used, there should be a 3mm led and a resistor with the bluetooth module. Using these components you can wire everything according to the diagram.

The power of the Bluetooth module comes from the amplifier. So if the amplifier is turend on by rotating the dial, the Bluetooth module also turns on. If the Bluetooth board was powered from the step-up module directly it would always be on and drain the battery in no-time.

The led has 2 legs. the long one is connected through the resistor to the 'LED' pin on the Bluetooth board. The short leg goes to the - pad on the step-up module.

Now the power connections are done, we need to connect the audio signal wires from the Bluetooth module to the amplifier. We only need 2 wires here and the 'left' or 'right' orientation does not really matter in this speaker. Solder the wires according to the schematics.

The last soldering job is to wire the speakers to the amplifier. On the speaker there are two small pads and next to the pads is a small indentation with a '+' or a '-' marking. Attach the wires to the corresponding pads on the amplifier. Again, the orientation of the left or right speaker is not so important because it is a very small speaker.

Now the wiring is done we can test the electronics before we mount it on the faceplate.

1. Make sure the amplifier is off by turning the knob until it clicks off
2. Place the 18650 battery in the holder
3. If everything looks fine, turn on the amplifier on a low volume.
4. If everything works you should see your led blinking and you should here a voice which tells you "Bluetooth mode" or something else depending on the bluetooth module you use.
5. Try to connect you phone to the speaker by pairing to the new device. My Bluetooth device is called 'WIN-668'
6. Play some music and test if both speakers are producing sound.
7. Don't worry about the quality of the music yet. This will improve drastically when placed in the bowl.

Some parts have a specific place on the faceplate, and some don't. Call it artistic freedom ;) Depending on the length of your wires you can hot glue the parts somewhere safe.

1. Begin by mounting the speakers. The key to a good sounding speaker is to use a lot of hot glue to seal the connection between the speaker and the faceplate. Please be careful not to hot glue the paper part of the speaker. Only glue the iron casket.
2. Mount the usb-c charger, 3mm led and the amplifier through the corresponding holes. Hot glue both in place and attach the screw to the amplifier to secure it even more.
3. The battery holder has its own space drawn out below the speakers. Mount it how you see fit
4. Now you are left with the step-up converter and the bluetooth module. Both have no predefined place on the faceplate. So glue them somewhere you see fit. Do not glue them to other electronics or on the speakers. This could cause electronic shorts between boards.

You can test the speaker again, glue it to the bowl and call it a day. I'm sure the speaker sounds great now and 9 steps is a long way to come, but if you are still reading there is still one more optional step: acoustic treatment.

The inside of the bowl is a hard smooth surface that reflects sound very well. This leads to resonants and can cause the music to sound a little bit weird. To cancel out this effect you can apply acoustic wool. Say what? Yes, but don't worry, we can also use pillow filling, foam or another absorbing material. Placing a small amount of this material in the bowl stops the waves from moving freely through the air and improves the quality of music. I challenge you to experiment with different amounts of filling and test the effect.

When you are satisfied with the sound you apply a generous amount of (hot) glue to the sides of the faceplate and close the speaker. This seals the speaker and it will sound at its best.

Have fun!