Introduction: Monobox 4" Amplified Speaker 15W.

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About: Hello everyone! I Ser S. 19 Y/o. I'm a college student in electronics. I spend most of my time working on my projects, and when not, I'm always in good company with friends that help me!. Always loved to tear …

Heeeello everyone!!

Back! Back again with a new desing for a portable speaker. This time, I will be showing how to build a very crude portable speaker (there goes bluetooth... sorry! ) However I will try to guide you step by step through the making and in the end, I will explain some downsides of the build (which many other portable speaker have) and In the end we get in our hands a very powerful speaker for a price that may seem a bit too low (Costed me less than 10€, but the fact I re-used some stuff)

Here are the main specifications:

  • 4" 2-way speaker driver.
  • Long run time, thus it is easily expandable.
  • Universal charge port. Charges with the same cable you use to charge your phone (micro usb), no need for an external adaptor.
  • Rather good looking finish.
  • 15w output power.
  • AUX input.

Any question, please don't hesistate posting it down below and also please feel free to comment our ideas and thoughts. Now let's dive right into to the build!

Step 1: Gathering the Needed Materials

The things needed for this build should not exceed 20€ but it will depend on the quality you want and wether or not you can recycle some stuff.

The materials can all be obtained online, however I encourage you to look around and try reuse what you already have. (For example, the aux input can be easily salvaged from other electronics and If you are lucky, you can even salvage lithium batteries). Finding some wood panels (mine is 6mm.) shouldn't be that hard and Im sure you have some unwanted piece of cloth lying around (Make sure sound can break through the cloth).

(All the links are from aliexpress)

  • Lithium battery charger with bluit in protection (TP4056)

For the most important part, the speaker, I got mine from a car related shop. There they always sell car audio equipment and where I live is the easiest way to obtain speakers. Refuse using those "full range" claimed speakers even if they are exaggeratedly cheap. My driver is a 2-way speaker, meaning that it has a woofer (for the lows) and a tweeter (for the highs) both in the same speaker. It is rated to 40w Máx, but we wont be able to use all of its power because it will be powered by a 15w amplifier.

And for the Tools needed, hare are the main ones used;

  • Table saw
  • sandpaper
  • wood glue
  • compass
  • some tape
  • some wires
  • screwdriver
  • some short screws
  • hot glue gun
  • soldering iron
  • clamps
  • knife cutter
  • stapler gun
  • dremel may come in handy
  • multimeter

I used EVA foam for the finish but there are many other options depending on your likes.

Step 2: Mounting the Speaker

The project is started by making a hole in the center of a piece of wood, which will be used to secure the speaker tight in place.

My dimensions are: 12,2 cm width x 12,2cm length (perfect square) with a thickness of 1cm. The internal circle has 4.7 cm radius.

The whole project is going to be built around this piece of wood, so make sure you take your time to make straight cuts. However, no need to care about the looking, as later on a piece of cloth will be covering the front.

I started by laying down those dimension onto the wood board. The exact center is given at the point where the two diagonals intersect. The material left inside the circle drawn will need to be taken out. With the marking work done, I proceeded to make some holes to be able to use the jigsaw. Use some sandpaper if necessary. Finally, 4 screws are used to ensure the speaker driver doesn't go anywhere.

Step 3: The Enclosure

The enclosure is made of 6mm. wood panels.

My dimensions are: 12,2cm x 7,5cm. each side of the box (Note that this is supposed to fit the previous step, so you may have to adapt the dimensions.)

Then we need to cut at a 45º angle degree on each side of each panel to be able to match the dimensions to the previous step.

Note: I recommend to make the holes for the on/off switch, the aux input and the charging input in this step because later on it will be a lot more difficult. (Yes, happened to me, you will notice on step5 ).

Step 4: Glueing the Enclosure

This step is pretty straightforward, as the only thing to do is to glue the 4 previously made panels to make the box. Put some tape on the back of the panel where it will fold over. Then apply glue on the 45º angle joints and secure firmingly the whole with 2 clamps (or more if necessary) while it dries.

Once done, we end with a box of 12,2cm by 12,2cm outter perimeter.(It should fit onto the speaker, if not, you can use some sandpaper)

Step 5: Audio Source & Inputs

If you followed my recomendation previously, now you may skip this step. If not, this will be the most complicating and time consuming step. Here is about making accesible the inputs(On/off switch, AUX in and charging port), to do it, lay where you want them to be and work your way up to make it happen. Don't be surprised if this gives you some headache... It certainly does. So I hope you used my experience and avoid this trouble :D

Step 6: The Class D Amplifier

squeezing POWAH POWAH POWAH!

This amplifier is a PAM8610, a dual amplifier capable of 15 watts per channel in a very small form factor which runs at 12v DC. As we are only going to use one output, we dont have to care about overheating issues (Anyways, the chip has high temperature detection, so even better).

In this step we only are going to solder the aux port to the board with two wires. The middle lead of the aux port is usually GND, so connect it where it says GND on the amplifier board (should be very close to the left and right channel inputs on board). Then conect either lead of the aux input to either channel input on the board. If you feel, you can solder some wires to the power in on the board (where it says +12v and gnd)

Note: Depending on which channel you connect the signal from the AUX input, you will have to ensure later on when connecting the speaker you wire it accordingly to the channel you have connected the AUX input signal (In a nutshell, If you connect left channel, make sure you also wire the speaker on the left channel)

Step 7: Getting Powah! (Batterries)

To power up the amplifier, we need some sort of energy storage. Lithium ion cells are the best idea nowadays, but you can always look for other options like lipo's but they are a bit more expensive.

In this case, with only one cell we are ready to go. However I decided to implement another cell (in parallel) to increase the overall capacity which means more run time. To connect them, solder wires to the positive and negative and respectively solder them to the charging module where it says B+ and B-.

Once done, we can check everything is properly soldered when conecting a micro usb to the charging module. Either a red or blue led must light up.

Finally, secure the batteries inside the box with some hot glue.

Warning: Li-ion cells are very dangerous. Handle them with care when using them as they are very sensitive to overheat, overvoltage, short circuits, physical damage, etc... To solder them, use some sandpaper on the edges first and then apply the solder. If you need more information about soldering them, you can check my previous instructables.

Step 8: Getting Powah! (Boosting)

The remaining conection are quite easy to finish. Start by conecting the step up module input to the output of the charging board. Always take care about the polarity. Using a multimeter on voltage, read the voltage output of the step up module, while slowly adjusting the potenciometer until it reaches 12 volts. Then connect it to the input of the amplifier (where it says 12v and GND accordingly).

Step 9: Mount & Secure the Hardware

Finally wire up the speaker ensuring the polarity is correct to the corresponding output of the amplifier.

Now you may proceed to a sound test. Conect it to a source of audio (your mobile phone for example) turn it on and it slowly increase the volume. It should sound clear proving the success of the build. The electronics part is completed, what's left is mainly final touches.

Now, hot glue everything and make sure it stays in place forever.

Step 10: Speaker Cloth

To make this step easier, you may desolder the speaker to work on it more easily. Grab some unwanted, but in good state cloth and cut it down to approximately 2cm larger than the front of the speaker from each side. Place it in the middle and start by applying some glue on the back of the panel (The wood glue I used before worked out fine). Then stretch the cloth over and secure it in place with some staples. Repeat this until all the sides are done and leave it to dry a couple of hours, before pulling out the staples.

Note: Choose carefuly the cloth you use, as some arent sound transparent. (Doesnt let the sound come out)

Step 11: Sealing Up

When all the neccesary test has been done, It is time to finally seal up the enclosure. First, cut a piece of wood with roughly the same dimension of the back of the box. Open two holes to show the status of the leds on the charging. In order to achieve the seal, apply abundant glue and spread it. Next place the piece of wood previously cut and move it a little bit up and down to avoid any air leakage later. Clamp it and leave to dry for a couple of hours.

Step 12: Sanding and Finish

When everything has dried, there may has been some imperfections, so go ahead and sand them down. Then we can proceed to the finish. I came with EVA foam for the sides and also for the back but feel free to use any other finishing idea/technique. In my case, it was just a matter of cutting the foam to size and glueing it. Allowing some time to let it dry we are approaching the end of the build.

Another good option is to paint or vanish the wood or even use wood polisher.

Step 13: The Result

In the end, the build turned out better than what I expected, mainly due to the use of cloth to "hide" the speaker. Another point is the power output, I was expecting a lot less from a single 10w speaker. And I also would like to point out that using a 2-way speaker is well worth it (Instead of using one full range driver). However, using separated drivers (woofer, tweeter) will always have the best sound quality and also sound pressure.

And well, we end up with a quite loud, long lasting, portable speaker which will surely outperform those cheap little brandless from china. And for the price of roughly 15€ (A bit more, a bit less depending on where you buy the parts)

Step 14: Conclusion, Final Ideas, Upgrades & Closing.

To enhance the build, having a bluetooth connection is a very good idea. Nevertheless, it raises the cost a bit and using bluetooth technology will drain the battery quite fast, so we go old school, a simple AUX cable and we are ready to rock!

To improve the build, we may use more 18650 lithium cells in parallel , this means greater a battery, more runtime. But it also increases costs, weight and overall size.

One of the main downsides of this project is the step up module, just beacuse it is not 100% efficient. That means some energy will be lost due to the conversion, and will drain the battery faster. Usually the efficiency is quite high. (greater than 80% in most cases). For example if we had a 1000mAh. battery, we would only be able to use 800mAh (1000mah * 0.80 = 800mah) which is, well, improvable. To solve this little problem we could either lower the output wattage so we can use a single cell powered amplifier (which means that runs at around 4 volts) or we use series cells battery combinations (3cells gives us around 12v and with 4cells we archieve 16v.). The problem comes when charging is needed, as we need a higher voltage source and the 5v of a usb wont satisfy us. The answer is quite simple, we just use the booster right before the battery, not after (this build). This still keeps a powerloss across, but we end up not wasting the energy stored on the battery. In a future build I will switch to this kind of circuitry so stay tuned.

Finally, I would really like to thank all of the people that in some way helped and supported me And also a big thank you to all the community out there ;)

"...the idea is to try to give all of the information to help others to judge the value of your contribution; not just the information that leads to judgment in one particular direction or another."
- Richard Feynman.