Custom-made Portable Speaker

Hello everyone!! I hope you'll like this project and learn something new!

This instructable is about building an affordable yet loud sounding, stunning look portable speaker. All the parts involved can be easily obtained through internet shops (Aliexpress, ebay, etc)or in your local store. Some can even be salvaged from old/unused electronics. This project is about designing an enclousure in Fusion 360, handcrafting our own panels and laser engraving them, as well as, mounting cool modern led's and switches. All culminating on a relatively small, compact, powerful speaker for its size which also looks awesome and elegant.

This speaker was designed with estethics in mind, not electronics. It may feature some electronic tricks, but nothing more complicated than soldering wires and measuring with a multimeter. Having said so, I really recommend building this speaker, since it is a pretty easy and straightforward proyect, and you end up with a powerful speaker yet stylish and pleasing to the eyes. Here are the overall specifications:

-Class-D Audio Amplifier based on TDA7492P (25w+25w) with integrated bluetooth conectivity

-4s cells lithium battery (14.8v 3400mAh)

- Two 2" speaker drivers capable of 10w nominal each

-Passive radiators to improve bass response

-Long battery run time (over 30h. continous)

-4 Leds indicate the battry left.

Features:

-3D printed case.

-Wood Laser engraved front and back panels for a very customizable appearance.

-Leather glossy finish.

Testing supplies

Here's a list of al the components and tools required. I sourced alll of the electronics through aliexpress, being the only downside having to wait a month for the parts to arrive. Thereofre, all the links are from aliexpress, since is a well known online website, has almost everything and quite cheap.

Tools:

• A 3d printer (optional: with a laser engraving add-on).
• A jigsaw (or a handsaw can get the job done).
• A multimeter (used for measuring voltages and currents).
• Screwdrivers.
• Drill.
• Soldering iron.
• Sandpaper.
• Scissors.
• Clamps.
• Kapton tape

• Silicone glue.

Materials:

• Fake leather PU (aliexpress).
• 6mm plywood.
• Wood Varnish.
• Nails paint.
• M2.5 screws & nuts.
• Hot glue.
• general use wire.

Electronics:

• Amplifier board TDA7492P (aliexpress) (alternatives).
• 2" Speakers rated at least for 10watts (aliexpress).
• Passive radiators (aliexpress) (I reccommend the 40-45mm option).
• Lithium 18650 3.7v 3400mAh. cells (aliexpres).
• Step down charging circuit XL4015 CC CV(aliexpress).
• DC power jack 5,5 * 2,1 mm (aliexpress).
• Battery level indicator (4s) (aliexpress).
• 16mm round latching switch (with light indicator) (aliexpress).
• BMS (aliexpress).

The heart of this portable speaker is the audio power amplifier based around the TDA7492P which is a 25w + 25w power amplifier. The board integrates the input stage being a bluetooth connection and the power stage (amplification) all together in one single board. the only disadvantage is that the board I bought has no AUX input, so the only way to play music is through bluetooth. (Note: You can find in aliexpress the same amplifier+bluetooth board with even the aux port feature at almost the same price).

The speaker is powered by 4 lithium ion cells, resulting in 14.8volts and arround 3.4Ah. of capacity (total power ≈50 Watthours). The cells are protected againts shorts, overcurrents, under-discharge and over discharge using a BMS. The battery is charged using a Constant current Constant voltage charging module (CC CV) Furthermore speaker also features status leds indicating the battery capacity left.

All of this results in a pretty good sound with decent bass and about 30+ hours of playing time, depending on the volume played. This is achieved thanks to the class D amplifier reaching up to 95% efficiency.

By following the attached wiring diagram and having understood it, there should be no problem putting it all together and working.

I decided to go for a pretty common design around bluetooth speakers. Using Fusion360, I modeled the enclousure, as well as the wood panels, just to render it all together and take a glance of how it will look. I uploaded both the stl (ready for printing) and the fusion360 file in case you want to tweak something.

I used RepetierHost to slice the stl generated on Fusion360 and print it. You can always use your preferred slicing software (Cura, etc.)

I recommend printing at 0.1 or 0.2mm layer height at 20-40% infill. Supports are necessary. Can be printed on a 20*20cm bed, but the stl needs to be rotated 45º to fit in. I printed in PLA without problems.

Arranging 4 lithium 18650's cells in series results in a battery pack of (3.7v * 4 = 14.8v) nominal voltage at the same Amp hours (mAh.), so since my cells are 3400mAh this gives a product of (14.8v * 3.4Ah = 50.32Watthours aprox.). I used 18650's cells since they are commonly found in electronics, thus they are easi to find and also relatively cheap but you can use any other li-ion battery, you can ebven use Lipo batteries.

To assemble the cells, as said earlier, we have to connect them all in series. This means cell1 postive to cell2 negative and so on. The physical connection should be done using a spot welder. Those machines are quite expensive and many of us dont own one or have access to, so the other option is to solder them. This is quite ricky and can be harmful to the cells, since soldering requires high temperatures and cells don't like that.

To avoid thermal damage to the cels, use a decent soldering iron (25w or more) and make sure it has reached the maximun temperature before soldering. During soldering, avoid contact with the soldering iron and cell for more than 2 seconds. This process has to be made very quickly to avoid any damage to the cell. You can use some rosin/flux to help the solder flow more evenly and stick better. Also, I always sand down a bit the surface of the cell with a fine grit sandpaper.

To connect each cell, tab wire has been used, but any wire can get the job done. Once thay are all soldered, I used kapton tape to firmly hold them together. Finally, we must add the BMS protection circuit. This circuit will check each cell voltage individually ensuring neither cell exceeds 4.2v (during charging) or drops below 2.9v (during discharging) ,as well as, protecting against short circuits. The connection is shown in the schematic(Note: the bms in the schematic it is not the same as mine, however, they all wire up the same way).

Remember: Lithium ion chemistry based batteries are very delicate. Treat them carefully, they can be very dangerous when mistreated

-Remember-
Lithium batteries are dangerous when misused. Be very conscious about what you are doing and never leave them unattend, especially at charging process.Also be careful not to exceed heat when soldering them together.

Finally, connect an XT30 to the output terminals of the BMS and add heatshrinking tube. This way the conecting and disconecting the battery is very easy and the wiring looks clean. This is optional, you can use any other connector you have.

Charging lithium cells is a very intricate and delicate task. Tipically, a CC CV charging algorithm is used to charge up li ion chemistry cells. The basic algorithm is to charge at constant current (0.2 C to 0.7 C) until the battery reaches 4.2 Vpc (volts per cell), and hold the voltage at 4.2 volts until the charge current has dropped to 10% of the initial charge rate. The termination condition is the drop in charge current to 10%.The charge cannot be terminated on a voltage. The capacity reached at 4.2 Volts per cell is only 40 to 70% of full capacity unless charged very slowly. For this reason you need to continue to charge until the current drops, and to terminate on the low current. This is the main reason we can not only use a CC module (Aka, boost/step up module). CC CV module boards are pretty easy to find on the internet (ebay, aliexpress.) and are quite cheap. For this proyect, I will be using a Buck converter with CCCV module to step down the voltage from 24v to the required voltage. You can identify easily a CCCV module just by looking at the images. If it only features one adjustement potenciometer, it is not a CCCV board, since the require at least 2 pots.

Another thing about these boards is that they claim high amperage (4-5A) but the overheat a lot. In my case, i was drawing about 1,5A and the module got really really high I had to add a heatsink to it. Nevertheless, even with the heatsink installed, it kept getting too hot, so i decided to cut the current in half to 0.6A - 0.7A resulting in a charge ratio of 0.2C (3.4A * 0.2 = 0.68A). This avoids stressing the battery during charging since it charges very slowly. Later, I checked the datasheet and the module has the ability to 4A, however, it is limited to 10watts of power without the need of external heatsink (natural convection) so my experience.

The board does it job. It charges decently the battery, however, once the powersupply is disconnected, a reverse current of 13mA appears. This will take some hours, but will end up draining the battery. In order to prevent current going backwards (from the battery to the charging board) there exist two simple methods. The first method is to add a mechanical 24v. relay (It should work also with a solid state relay, but I havent tested that option). The relay will connect the battery to the charging board when the power supply is connect and accordingly, disconnect the battery from the charging board when the power supply is disconnected. To do this, the coil of the relay is connected to the power supply of 24v. Then, the battery positive is connected to the Normally Open circuit of the relay. This way, only the battery will be electrically connected to the board when there is a power supply connected.

The other option I wanted to try out is simply using a diode at the outut terminal of the charging board. This forces the current to only flow one way (that is, from the charger to the battery). I used two 1N4007 connected in parrallel (although using only one should work, since they are rated for 1A) soldered to the positive output terminal of the charger. Note the polarity of the diode.

To adjust the module, the first thing to do is to set the voltage accordingly to the required charging voltage. I will charge each cell to 4.15v so that means we have to adjust the output voltage of the module to 16.6v (4cells * 4.15v = 16.6v) but we have to take into account the diode forward drop voltage (around 0.7v). Adding up, this makes 17.3v which is the voltage we have to set up using the adjusting potenciometer (the one that iscloser to the input terminal). Next comes the CC adjustment. The battery must be drained in order to procced. One way to do this is to connect any load to it and wait until the voltage reaches 3.0v per cell (11.8v in total). Then connect an amp meter to the battery and conect the charging module. It will start charging inmediatly, so be careful if you are using a beefy power supply. Adjust the current flowing using the potenciometer that is closer to the output terminal until the current is about 600mA-700mA. going higher than this will charge the batteries quickie, but the module muy overheat as I explained before.

You may also notice I desoldered the blue terminals and just soldered wires to the board. This is to reduce the volume slightly and get a cleaner look.

Summary: Desolder the terminal blocks. Adjust the voltage to 17.3v and set the current to 600-700mA. Add a general use diode (1N4007) to the output of the board.

The power button is just a mere switch with a led indicator. The job of the switch is to connect and disconnect the amplifier. The power button has many pins, but the ones we will use are; the common pin (marked with a C), the NO (normally open), and the power +/- for the led. The led is supposed to work with 12v, but our battery voltage is way higher, so we need a resistor to drop down the voltage a little bit. The first thing is to measure the current the led draws at 12v with a current meter. In my case, 8.7mA. Next we have to calculate the voltage drop we need in the resistor. Our supply voltage from the battery is 16.8v minus the working voltage of the led 11.8v means the resitor must create a voltage drop of 5v. Using ohm's law (V = I * R) we can calculate the required resitor value since we know the current that will flow (8.7mA) and we also know the voltage at the resitor (5v.). R= 574 ohms. I used 680 ohm because it was the closest resitor value I could find.

The connections are the following:

- Common: connected to the postive of the XT30 connector

- NO: connected to the amplifier (positive)

- The negative of the led will be conected to ground

- The positive of the led will be connected to the resitor, which willl be connected to the NO aswell(this way, it will light up when the amplifier is connected).

Next, connect the XT30 connector, and leave 8-10cm of wires for the charging board, the amplifier, and the status led board.(Check image)

Remember to use shrinking tube to prevent any shorts at the pins and to make it look cleaner.

Basic woodworking skills. I used the 3d printed enclousure as a template to draw the shape of the front and back panels. Although they should be identical, I recommend you to cut the shape in paper and checking it fits, before cutting the wood. To do all the woodworking cuts, I used a jigsaw. Once the panels were cut, I sanded them down a bit and ensured a nice fit on the 3d printed enclosure

The front panel is very simple and straightforward. Take the front panel and draw a center line where the center's speaker holes will be. Next, measure the diameter(using a calipper) of the speaker where the rubber ends. I used 13cm distance between the center holes, but you can use whatever distance you may like. Using a handsaw cut out the holes. Finally, mount the speaker drivers, mark the position of the mounting holes and drill the necessary holes for the screws. I used 2.5mm* 12mm M2.5 screws and nuts. The same screws were also used for the back panel mounting. To drill the corresponding holes for the back panel, mount it and then use a tool with a sharpy/pointy end (I used a small screwdriver) to punch a small mark. Using the marks as a guide, open the necessary 2mm holes using a drill.

The push button that comes with the level indicator is not very handy, thus we will add our own momentary push button. First this is to desolder the original button and solder 2 wires that will connect the new momentary push button.

To mount the passive radiators, use the same procedure as explained before. Summarized, mark the position of the components and cut out the necessary holes. Do the same for the power jack. For the battery indicator, drill four 1mm holes for the led light to shine through and another hole for the momentary push button.

Once the wood panels are cut and fit smoothly, comes the wood polishing. Since my wood was pretty "whitish" i decided to stain the wood to a darker color. Then I applied wood varnish. To do this step, you should follow the instructions given by the manufacturer of your wood varnish. You should end up with a pretty looking and glossy wood panel. Let it dry for a few hours (depending on your varnish) to proceed to the next steps.

While the wood panels are drying, it is possible to work on the leather that will cover the 3d printed enclosure. Cut 2 pieces of leather just the lenght of the enclosure and leave 2-3 cm working room. This way, one piece of leather must cover half the enclousure (bottom or top) and have about 1-2cm sticking out enough to wrap it between the wood and the 3d printed enclosure. Sew together the 2 leather pieces at one end (I used a sew machine because it was faster, nevertheless, you can always to this by hand) so that, once reversed, the thread can not be seen from the outside. Then place the leather on the enclosure and repeat the process for the remaining end and making sure that the threads end up simetrical at each end. You can go for a pretty snug fit if your leather is strechy.

This step is optional. Having a 3d printer which can be converted into a laser engraver makes a good idea to engrave the wood panels since laser engraving looks awesome and looks profesional and clear. I wont go into detail here, but the main pont is to load the wood into the 3d printer bed (now acting as a laser engraver) and engrave your desired logo, photo, drawing or whatever you like. Always be careful when working with lasers and always wear safety glasses while the machine is powered.

Once the wood panels were engraved succesfully, I coloured some of the details and proceeded to apply some wood stain. Then I also painted the edges of the speaker holes with nail polish (you can use whatever paint you desire, I just wanted to use the nail polish since it was lying around for a long time.). The final step for the panels is to varnish them. Before doing this, make sure all the components fit nicely and everything is correct. The number of layers of varnish depends on your product and how you want the final look.

Having dried the wood varnish, it is time to permanent mount the all the elements to it, starting by using some silicone glue to ensure an airtight seal betwwen the passive radiators and the wood. Also, glue-down the battery level indicator and the push button ensuring air can not get through. While we wait for the silicone/glue to dry, we can proceed to the next step.

Now it is time to place and glue the leather in place. Start by sliding it into the enclouse and glue only the edge, not the full body. Use some clamps to help the leather stay in place while the glue dries.

Now, similarly to the previuos step, seal the front wood panel to the enclousure. I added some more glue to the gap between the leather and the enclousure, and finally mounted the panel. Ensure a perfect airtight seal from the inside by using silicone glue where the wood and the plastic meets. Beware for any excess glue leaking and damaging either the wood or the leather. Once dried, you can mount the speakers using its correpondent screws.

Using a cutter, open a hole for the pwer button to go through. Also, now it is a good idea to glue-down the leather to the enclousure body. This way we avoid any ridges forming.

Ensure the charging board is properly adjusted and then proceed to mount it and permanently glue it to the wood panel. Since it will get hot, I used epoxi resin based glue. Avoid using hot glue here, as it will melt. Next insert the power button and its corresponding wires and secure it in place with its corresponding nut from the inside. Finally, solder the charging wire to the board.

Once the case and panels are done, it is just a matter of conecting everything together. First of all, I added a heatsink to the IC on the amplifier to improve thermals thus reducing temperature. I also desoldered the terminal blocks on the amplifier board. With the help of some scrap 6mm wood and some hot glue, I mounted the amplifier just on top of the battery pack. I had to do this due to the BMS because it was in between. If you follow this instructable, try to hide the bms anywhere else, not on top of the battery like I did.

Before soldering the speakers to the amplifier board which is the next step, it is a good idea to set the amplifier to match the maximum power handling capability of the speaker. In this case, the speakers are rated for 10watts nominal (aka known as RMS or eff). In electronics, power is equal to voltage times current (Power = V*I) and by applying the ohm´s law we end up with this formula; Power equals voltage squared over the load (Power= V^2 / R) where the load is the coil´s resistance of the speaker, and the power is the nominal handling power of the speaker. Therefore in my case (10w and 8 ohm) this results in a voltage requiered of V=√R*P=√8*10= 8.94v. This is the voltage at the output of the amplifier (without the speaker connected) to reach a power output of 10 watts. Using a multimeter, connect the probes to one channel of the amplifier and set it to measure AC voltage. Connect the amplifier through a bluettoth device and set its volume to max. Then gradually increase the amplfier volume using the corresponding on board button until you reach aproximately 8v. Now you can proceed to the next step and connect the speaker.

Note: Exceeding the nominal power handling capability of the speaker may cause severe damage to the speaker by burning its coil. I reccomend going for only 8-9 watts nominal. Also, class D amplifier tend to distort a lot at high volumes, so it is a good idea to stay at relatively medium-high volumes.

Then, the speakers are soldered to the amplifier making sure the polarity marked on the speaker and amplifier board match correctly. Likewise, solder the power wires to the amplifier.

At this point, everything should we working fine, so it is time for a test. Turn it on, and test the amplifier. Look for excesive thermals at the battery/amplifier or any wire. If everything is ok, we can proceed to the next step.

Ultimately, glue down the remaining leather to the enclousure (cut the excess if needed) and clamp it while the glue dries. Use some double sided tape (Or hot glue) to attach the battery to the bottom of the case. Solder the DC power terminal to the charging circuit and solder the battery indicator too. Remeber to use heatshrink tube to prevent shorts from happenning.

To improve accoustics, grab some cotton and place it inside the case. This should help a little bit with the bass extension.

Due to improper design of mine, 2 screws that hold the back panel in place overlap with the battery inside. The solution to this is to cut down those 2 screws to fit the size. Other than that, the build is completed.

Overall, it is a pretty looking build and fully functional portable bluetooth speaker. Sounds very good, wirh a filling bass, plenty of battery life at high volume and has a very nice looking and finish. The dark varnished wood matches ver well with the black leather and the laser engraved letters really gives a stunning look. also, if not taken into account the manufactring process of 3d printing and laser engraving, the electronics are quite cheap (less than 50€) and some components can be salvaged from scrap electronics. The lithium cells can be easily found on laptops and other electronics. The DC port can be salvaged and so the wires. Also, there is no need to implement passive radiators if you are not looking for a punchy bass response.

However, this is my second design in portable speakers, so there is a lot that can be improved. For example, mounting the amplifier close to the batteries is not a good idea, since the amplifier will get hot and thus the batteries too. The dimension of the battery pack should have been taking into account while designid the enclousre, to avoid the screws from overlaping. This can be easily solved just by separating a bit more the screw holes.

Charging by micro usb is a feature I forgot about that is quite important. Being 24v the only way to recharge the is inpractical since finding a 24v power source outdoors is pretty uncommon. Also, having a 5v usb female port is a nice feature, so you could even charge your phone while playing music.

The bluetooth connection works quite well, however, it drains the cell phone battery and sometimes is just convenient to have an auxilary (AUX) input for the sound to avoid connecting via bluetooth. Also, for the bluetooth conectivity, a control panel could have been designed. This control panel is a set of buttons that play/pause the music and control the volume.

Despite the big enclousure, the space is not very well optimized.There is a lot of tangled wires and the wiring looks kida messy. Accessing to the electronics becomes a hard time if you need to tweak anything inside. Also, for the size it has, it could soun louder just by upgrading to a more powerful amplifier. The battery runtime is a bit oversized (however this is never a downside) and the speakers are capable of handling a bit more watts. The problem comes we when want more power. More power translates into more heat and it must be dissipated, otherwise, the temperature will start to rise and things can get dangerous with a lithium battery close.

To sum up, emphasize the excellent quality and sound of the speaker. You won't find any afoordable consumer speaker looking so dope as this one.

It has been a long proyect for me. It took 4 months from idea to reality, but in the end, Im very happy with the result and I've learned a lot and improved my skills down the road.If you have any questions feel free to ask down below in the comment section. Or suggest an improvement, I will try to answer as quickly as possible. :)

-SerS.