DIY Speakers

Learning CAD, 3D-printing tolerances, and fitting.

6 min readNov 1, 2021

I build software, and I’m not an electronics wizard. For me, the best user interface is the command prompt. Why do I say this? Because if I can do this, you can too.

Every once in a while, I like to build things. Things that are a bit more tangible. Inspiration this time came in the form of Arvind Sanjeev and watching him assemble a custom speaker set. What caught my radar was the entire process of making it and the multiple degrees of freedom, albeit a bit time-consuming. You could always buy a good set of speakers off of the internet. But where’ the fun in that.

This was more like the grownup version of Legos.

But why would anyone want to assemble their own speaker set? Why won’t you buy a good, factory-made set off the shelf? For me, there are a few reasons.

I recently set up my work desk at home. I love some background music while I work. Up until recently, I was using my headphones. But after a day of online meetings, I no longer wanted to put on the headphones. I was on the lookout for a good set of speakers when I stumbled upon this option. So for me, the reason was customizability.

The side-mission in this quest was for me to spend time and pick up CAD skills. Something which I have been planning to learn but couldn’t find a good enough reason to. Now I do.

Components and equipment

2 x Peerless by Tymphany TC Series TC8FD00 3″ Full Range Speaker 4 Ohm
2 x Peerless by Tymphany 830878 3–1/2″ Passive Radiator
Diycart TPA3110 Dual ic 30w+30W Digital Stereo Audio Power Amplifier Board with Inbuilt Bluetooth 12V-24V car for USB Speaker, Portable Speaker (As of writing this post, this is out of stock)
3.5mm stereo audio jack socket. 5 nos.

Additional equipment and software,

A borrowed 3D printer — A Prusa i3 MK2, thanks to Arvind.
Autodesk Fusion 360
Ultimaker Cura

I had a few AUX cables lying around at home, so I’m not including those.

Designing

I use the middle monitor as my main work screen, the laptop to the left, and the secondary display to the right with the current work setup. I wanted speakers to the left and right with a control box in the middle. I’m right-handed, and I prefer the speaker control box to be a bit offset to the right from the center.

I wanted a control box. It offers a bit more freedom while setting up the speakers. I can move the speakers closer or farther, and all I would need would be a long aux cable. The speakers would be to the left and right of this setup and the cables concealed under the table. Hopefully, the only cable that would be visible would be the audio output from the laptop.

Control box

Now that we had finalized the layout of my desk and where I would be placing the control box, I had to make provision for the following.

AUX IN on the left
L and R AUX OUT on the right
Power on the right

This is how the control case ended up looking in Fusion 360

Input on the right, 2x output + power on the right

Speaker box

The speaker boxes were pretty straightforward. I had to account for a speaker, a passive radiator, and a 3.5mm audio socket per box.

Printing

Once the design was finalized on Fusion 360, the plans were exported as STL files and were brought into Ultimaker Cura.

In Ultimaker Cura, once the optimal placement and orientation for the best way to print with minimal wastage was decided, the estimates were like this,

Control box: approx.10hrs
Speaker boxes: approx. 1 day and 8hrs per box.

So the speaker boxes were going to take a bit too long to print. This was primarily due to the size. Each box was 130mm X 130mm in dimension with 2 large holes in the faces. That’s a lot of support structure. I was beginning to think of an alternate way to make the speaker boxes.

Around this time, we ordered Starbucks coffee. The coffee came packaged in a card box. The box itself was pretty strong and was a clean fit for the speakers. So I decided to give these boxes a try.

We ended up ordering coffee again as the first few boxes were sacrificed for testing the right speaker fit.

Sacrificing these boxes revealed a few issues with my 3D design. The holes for the speaker and radiator cannot be on adjacent walls. The backsides of them would touch. I could make the box a bit longer or make the holes on opposite walls. But that would take time in printing.

So I ended printing the control case and using the Starbucks boxes for the speakers.

Tolerances and Fitting

Walter Lewin, in his famous lectures and in his book For the Love of Physics (For the Love of Physics: From the End of the Rainbow to the Edge of Time — A Journey Through the Wonders of Physics by Walter Lewin, Warren Goldstein), talks about the uncertainties involved in measurements. I got a crash course and an excellent practical lesson to always factor in uncertainties in measurements.

While printing using the 3D printer, I had to factor intolerance of 0.02mm. This means that for every hole, I had to add 0.02mm for a comfortable fit. Take, for example, the 3.5mm audio jack socket.

Measurements for 3.5mm stereo audio socket

The outside diameter of the socket is 6mm. In the 3D model, the bore was also set to have a 6mm diameter. Once printed, I had a tough time trying to fit the socket from the inside.

The same applied to the fitting. Each wall was given a thickness of 3mm. The length of the 3.5mm audio socket was around 4mm. A 1.5mm recess was made inside the walls to fit the socket with the screw it came with. This made a world of difference and gave the socket a solid fit.

Notice the recess in the inside wall for the 6mm socket.

Final assembly

Before soldering and assembling the whole thing, I wired up everything and ensured that the amplifier and speakers worked. Using this opportunity, I confirmed and labeled the pins on the amplifier. The amplifier, by default, works only via Bluetooth. I had to spend a few minutes figuring out the reset option or if there was one. Luckily it was there, and I shorted it to enable AUX input.

Trying to assemble things in the control box revealed a few drawbacks with my design. The first one was with the tolerances I mentioned above. The second one had to do with the small spaces in the design. This led to a tough time in getting things assembled. After spending a few minutes getting my fingers scratched and cursing, it was all done.