speaker – BlockWorker

BlockBox v2: The Actual Conclusion

After the completion of the BlockBox v1, I really thought for a while that I’d be done with this idea. And it only took a few months for me to prove myself wrong, with the BlockBox v2 project.

But this time it felt different – I really was done, at least for now. The BlockBox v2 has its flaws, there are certainly ways to improve it further, but overall… I’m just really happy with it, and very proud of the results of my work – especially if I look at both speakers next to each other.

Let’s look at the features of the final product:

Two-way cross-over speaker system with digital audio path
100W 10″ low-frequency driver
50W hi-fi tweeter
-3dB bass roll-off frequency around 38Hz
Theoretical maximum sound pressure level around 110-113dB (@ 1m)
Bluetooth audio playback (SBC or AAC), effective range ~10-15m
Touchscreen interface with lots of audio settings and playback control
EQ-optimised sound profile (to the best of my abilities)
(Roughly) music-synchronised LEDs
166Wh battery (in practice, lasts for more than 10 hours of continuous playback)
Battery protection and fast charging
2x External USB (5V 1.5A) for phone charging
Optional analog AUX input (not implemented due to lack of practical need)

Looking back at this huge project of building two speakers, I can only say one thing: It was absolutely worth it.

Now, are the speakers by themselves worth it? No, not really. Because I had to buy everything in single-piece quantities, restrict myself quite heavily in terms of what I could work with using the tools I had, and over-engineered many things “just to be safe”, they ended up being wayyyy too expensive to compete with commercially available speakers – and that’s if I ignore the cost of the months of work that went into them.

But the main value of this project, for me, was not in the speakers themselves, but the incredible amount of learning and experience that I gained throughout this project, including audio engineering, mechanical design, CAD and manufacturing, electronics design and soldering of course, and microcontroller firmware development.

This is where my speaker-building journey would end for now, but I had a feeling I would be back to it sooner rather than later, in another project.

BlockBox v2: The Build, feat. CNC machining

Just like before, the build process started with the electronics. So it was time to order new circuit boards and components.

Building the electronics for this second speaker followed the exact same procedure as I described for the BlockBox v1, so I won’t repeat it here. In the end, I had another nice circuit board that looks just slightly different from the first version (shown without the amplifier heat sink here).

Then, it was time for firmware development. This would be a much bigger task than it was for the BlockBox v1, again, because I had to implement a central system controller, as well as touch display communication.
I was able to find a community-made library/driver for the FT81X graphics processor in the display module, which certainly made the job easier, though I had to make quite a few modifications to make it work on the PIC32MZ microcontroller. Aside from that, I implemented my own serial communication drivers for controlling the digital audio processor, Bluetooth module, LEDs, and other peripherals, as well as some central system management logic connecting them together, and of course a user interface for the touchscreen. The firmware source code is available in the same GitHub repository as the electronics design files, though I cannot guarantee anything about its correctness, completeness, and especially code quality (I was quite careless sometimes back then).

When it came to building the enclosure, however, I knew that my methods from the BlockBox v1 would not be viable any more. Making smaller and simpler shapes using my hand saws may have been possible (even if tedious), but the more complex and much bigger pieces needed for this project would just be too much to ask for. Especially considering the idea I had for LED-lit logos on the sides, which require quite significant precision.
The translucent parts for the LEDs, as well as some black decoration and cover plates, were laser cut out of acrylic plastic, which I was able to order relatively inexpensively.

As for the main enclosure walls, I decided to use CNC milling – thankfully, though a personal connection to a machine shop at my university, I was able to do so for free, as long as I brought the materials and my own CNC programs.
Materials were easy, I just ordered some plain 12mm plywood panels, already cut to the sizes I needed, and got a small piece of aluminium plate stock for the connector panel.
The CNC programs were more complicated – Fusion 360 has some great tools for CNC programming based on my CAD design, but as I’d never done anything like that before, it took me a while to research, understand, and learn the basics of machining and CNC programming.
In the end, it was time for some machining.

This could be milled much more quickly with a higher tool RPM, but this machine can’t do more, as it was mostly designed for hard materials. Anyway, I was not in a rush.

With that, I had some rough-looking side panels, which would need quite a bit of post-processing to remove extra tabs and pieces, sand down sharp/rough edges, file away unwanted internal corner radii, and so on.

After post-processing, they looked much better, and also fit the acrylic pieces nicely.

Now it was time to assemble the speaker. I built the main wooden box by screwing the walls together using metal corner pieces, then hand-cut some extra plates with LED strips to go behind the acrylic inserts, installed the drivers, port resonator, display, circuit board, connector plate, battery, and some plastic wool for acoustic damping inside the enclosure.

With everything connected and closed up, the BlockBox v2 was complete.

However, since my circuit had a nice digital audio processor that I could control, I decided to improve the sound a little more, using some EQ optimisation.

BlockBox v2: New Speakers and Enclosure

Since the main source of my “disappointment” with the first BlockBox was the lacking low bass frequency range, that exact point became the springboard for the design of the second version.

Knowing that I wanted a lot more bass, I started looking into better speaker drivers for it. I found quite a few options that would offer me a complete bass extension down to ~20Hz, but nearly all of them meant sacrificing quite a bit of efficiency. That would mean either increasing the maximum power, which is difficult on battery-powered systems and makes the circuit design harder, or making the speaker quieter.
But come on, there’s no way I would allow the second version to be quieter than the first version – that would just make it feel inferior from the start.

So high efficiency remained a very important consideration in my driver selection, and eventually I found a new low-frequency driver that looked great for my needs: The Beyma 10BR60V2.
Since it had a lower effective frequency range than the BlockBox v1 driver, I also needed a new tweeter with the ability to pick up higher midrange frequencies. I ended up choosing the Monacor DT-28N, which was also just a higher-quality driver compared to the ones I used for the first version.

There was, however, a very significant difference from the BlockBox v1, with this driver choice: Size.
While the first speaker used a 6.5″ driver that could achieve good performance with an 8-9 litre enclosure, this new low-range driver was quite a lot larger at 10″, and according to SpeakerBoxLite, its optimal enclosure volume was somewhere around 61 litres. Yikes.

This prompted me to take a step back and think about it for a moment. Would such a huge speaker even make sense for what I wanted? It’d certainly be much more difficult to carry around.
However, I realised that with the right form factor, it may be possible to attach some straps to the speaker and carry it around like a giant backpack itself. The idea was certainly cool enough to make me want to try, so I continued with this choice of drivers.

The enclosure size I ended up deciding on was 55 x 40 x 35 cm, with a 10 cm vent port (Monacor BR-100HP), and walls made of 12mm plywood:

According to the SpeakerBoxLite calculations, with this design, I should be able to achieve a -3dB bass roll-off frequency of 38Hz – certainly a lot better than the first version. It wouldn’t be quite as “precise”, with a slight over-emphasis around 57Hz (+3dB), but I was willing to accept that, especially since audio pre-processing could fix that if it annoyed me later.

Based on this, I once again created a CAD design in Fusion 360, allowing myself to be a bit more ambitious with the features this time. The BlockBox v2 would have some protective rubber corners, much better LED lighting (including lit logos on the sides), a nice aluminium connector panel on the side, and even a touchscreen display for user interaction (instead of the basic buttons of the first version).

Of course, the electronics would need some changes to go along with these new features, as well as some upgrades to address some of the shortcomings I noticed with the first version. So, naturally, that was the next step of the design.

BlockBox v1: The Conclusion?

With the end of the BlockBox v1 build, I had finally accomplished my long-time ambition of building my own Bluetooth speaker – it really felt like I had reached a new level in my electronics projects, with the ability to build more complex systems.

Let’s summarise the features of the completed speaker:

Two-way cross-over speaker system
100W 6.5″ bass/midrange driver
Two 15W tweeters
-3dB bass roll-off frequency around 72Hz
Theoretical maximum sound pressure level around 110-113dB (@ 1m)
Bluetooth audio playback (SBC or AAC), effective range ~10-15m
(Roughly) music-synchronised LEDs
166Wh battery (in practice, lasts for more than 10 hours of continuous playback)
Battery protection and fast charging
External USB (5V 1.5A) for phone charging
Optional analog AUX input (not implemented due to lack of practical need)
Diagnostics LCD for showing battery and Bluetooth status

Sure, there are many imperfections and mistakes in the design, as is expected for my level of experience at the time, and I tend to focus on these imperfections too much myself when looking back at it.

But taking a step back, looking at the bigger picture of what I built in the BlockBox v1 – I’m very proud of it overall. It’s a powerful, functional, portable speaker, and while its audio quality isn’t “hi-fi” by any means, I would also never call it bad, it’s certainly good enough for most use cases.

However, just being proud of it was apparently not quite enough for me. Yes, it was a good achievement for me, but I wasn’t quite satisfied. The bass roll-off was too high for my taste, the button control scheme was too basic, and the low-volume audio output was too noisy.

And thus, just a few months later, the BlockBox v2 project was born.

BlockBox v1: The Build

The first part of the BlockBox build process was the circuit board. Once my custom boards arrived, along with the components for them, I decided it would be best to build and test the power supply circuits first.
Because battery management is not trivial in itself, I would start with external adapter power – which I needed to get from somewhere. So, it was time to modify my laptop power supply, adding a compatible connector.

With that done, I could solder the necessary components for basic power path.
This was followed by constructing the main switching power supplies (52V, 12V, and 5V), allowing me to test that they work and produce the desired voltages.

Next, I added the Bluetooth module and auxiliary controller, as well as the corresponding connectors and support components.
I also soldered the power amplifier chip, since its small pin pitch would make it annoying to solder with more components in the way later.

To do any real testing, I would also need the user buttons mentioned in the previous post. They were soldered on a separate little board, to be inserted into the enclosure later.
I chose some nice tactile buttons with LED backlights. They also support custom labels to be inserted into them, for which I took some printable transparent foil, resulting in presentable, self-explanatory buttons.

After adding the rest of the analog audio path and amplifier output stage, the circuit was ready for testing and firmware development.
And yes, some of the power amplifier output components (especially the inductors) were severely undersized in hindsight, leading to more distortion at high power.
As you can see, the amplifier also got a heat sink, along with a temperature sensor and a temperature-controlled fan, which worked quite well.

During firmware development, I also realised that my initial idea for LED music synchronisation didn’t work – so I had to work around it, and the results were quite mediocre, but still did work somewhat.

Finally, all that was left was the battery protection and charging circuit, as well as some transistor heat sinks, and we have a complete and working circuit board!

Speaking of the battery – that needed some assembly as well. I ordered 16 Li-ion cells (in the standard 18650 size) with pre-installed spot-welded nickel tabs. To keep them arranged nicely and safely, I also got some plastic cell spacers.

These cells were then arranged into four groups of four, creating the desired 4s4p (four series, four parallel) configuration.
I soldered the four parallel groups together, before using some solder wick to connect them in series.
Soldering isn’t ideal, as it could overheat the cells – spot welding is the way to go, but needs tools I don’t have, so I just had to carefully solder the nickel strips – it ended up working out quite well.

Now I could get to the last piece of the puzzle: The enclosure.
I didn’t have access to the ideal tools for such a build (CNC mill, or at least woodworking power tools) – so I made everything by hand out of plywood stock, using a drill, various hand saws, files, and sandpaper. The resulting cuts were far from perfect, but good enough for this project.

For the RGB lighting, I glued RGB LED strips to some acrylic rods, before gluing everything (except for the back wall) together to create the enclosure (just missing the side compartment in this image).

The only thing left to do now was to install all of the components inside it, and I had a complete BlockBox!

This would be the time to say something along the lines of, “That concludes the BlockBox project, thank you for reading”.
But… let’s not rush it.

BlockBox v1: Speakers and Enclosure

As I started my research into designing the BlockBox, I realised one thing: Speakers are really complicated.
So many speaker drivers to choose from, priced anywhere between affordable and astronomically expensive, with different sound profiles, efficiencies, features, and drawbacks.
And what the hell are “Thiele/Small Parameters”?!

Hours of research later, I figured out what most of these things mean, and found out that the final size (volume) of the speaker would play a major role in the low-frequency sound design. Since most commercial Bluetooth speakers are very small, I always imagined making one of a manageable size too – so that is what I decided on. It’d still be larger than the typical “handheld” mini-speakers, but small enough to fit in a backpack.

Finally, I decided on a set of speaker drivers to use for this project. I wanted my speaker to be loud, so driver efficiency was very important, and my budget was quite limited, of course.
Therefore, I went for a two-way crossover speaker, using the 6.5″ Monacor SP-6/108PRO as a bass/midrange driver, and the Monacor DT-74/8 tweeter (or, in fact, two of them – mostly for the sake of symmetry, as you will see later).

In order to get the most out of these drivers, the design of the enclosure was quite important. Using SpeakerBoxLite, an incredibly useful free tool for speaker design, I determined that a vented enclosure with a volume of 8.7 litres would be perfect given these drivers and my size requirements.
Combined with a port resonator of the correct size (Monacor BR-50HP), this results in a 33 x 26 x 13 cm speaker enclosure with 10mm plywood walls.

According to the SpeakerBoxLite calculations, this should result in a flat frequency response down to 90Hz and a -3dB roll-off point of 72Hz. Not great, especially for fans of music with lots of bass (including myself), but not terrible either.
I’m sure it’s possible to do better within the constraints of this project, but all better options I found back then were too expensive, too inefficient, or just too complicated for me, as a beginner.

Based on this rough sketch, I created a more detailed enclosure design in Autodesk Fusion 360 – featuring all drivers, some translucent bars for LED lighting, a cutout for buttons to control the speaker, a side compartment to house a diagnostic display, the main power switch, and connectors for charging etc., and of course, enough space in the back for the battery and electronics.

With that out of the way, it was time to move on to the electronics design.

The BlockBox Project

Before I even started my first electronics project ever around 2017 (at age 16-17), I already had an idea on my mind: I wanted to build my own Bluetooth speaker someday.
Why? I’m not sure myself. Maybe it was just a naive ambition of a curious teenager, maybe I just wanted to look cool at parties as “the guy who built his own speaker”, or maybe there was something else that interested me about them.

As I was starting out with no real electronics experience and very limited knowledge, the idea of building an entire speaker by myself seemed nearly unattainable.
I would have probably been able to make something by buying and chaining together pre-built modules (battery management, Bluetooth receiver, amplifier, etc.) – but this approach, while quite popular in beginner DIY/maker spaces, has never felt appealing to me. It just felt like it wouldn’t really be my project, but just an amalgamation of others’ (commercial) projects.
Therefore, I put the idea aside, though it never left my head entirely.

Eventually, in 2019, I felt ready to try my luck at actually building such a speaker, from the ground up. And thus, the BlockBox project was born.
Looking back, I was still naive and clueless about a lot of the intricacies involved, but despite that, I feel it would be wrong to call the project anything but successful.

Start here to read the full story of the BlockBox project.

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