Open source software is all the rage; open collaboration with every software developer on the planet has led to more secure and innovative code. But what about on the hardware side? Traditionally, hardware has been more proprietary and closed off, but now with the proliferation of 3D printers and affordable single-board computers (SBCs) like the Raspberry Pi, we now have the ability to build and modify our own gadgets and devices.
Figure 1: 3D printed Ploopy Headphone components
That’s exactly what brothers Colin and Phil Lam were thinking when they designed the Ploopy open source Headphones. Every single piece of the Headphones is customizable. Hardware parts are 3D printed, and with an active community creating new designs, the possibilities are endless. Examples include tweaking the design of the Helmholtz resonators for different frequency responses or modifying the firmware to enable additional functionality.
The brains of the Headphones are based on the Raspberry Pi Pico with the RP2040 processor. The RP2040 takes care of USB interfacing duties as well as EQ functionality. Naturally, all source code is available on Ploopy’s GitHub, enabling users to experiment with modifications. The digital to analog converter (DAC) is the TI PCM3050, which converts the incoming I2S signal to analog and sends it to the drivers.
Figure 2: Raspberry Pi RP2040
The most important question is: how does it sound? Ploopy tested the frequency response of the Headphones against the well regarded Sennheiser HD6XX and found that they compared very favorably. Of course, the Ploopy’s open source nature means that if any improvements are made in either hardware or software, they can be easily incorporated.
Figure 3: Frequency response comparison: Ploopy Headphones vs. Sennheiser HD6XX
We sat down with Colin to get a little more background on the Headphones, the company, and working with the Pi Pico and RP2040.
Give our readers a quick overview of the Headphones, and its advantages.
Colin Lam: The Headphones are completely open source; the mechanicals, electronics, and firmware are all freely available. The big advantage here is customizability. The hardware shape makes a big difference in acoustic properties; it can be freely modified and quickly made using any 3D printer. The firmware can be used to shape custom DSP profiles, and it's free to modify. To sum up, the biggest advantage is that these aren't Ploopy's headphones; the design can be tweaked and changed by anybody.
How did you come up with the idea?
CL: It was the sort of thing that we wanted for ourselves. Locking up audio devices behind barriers of intellectual property rights and obfuscated manufacturing methods doesn't really provide benefits to listeners. Putting the design into the hands of the listeners just makes the designs better and more accessible.
Can you give us a quick look into your development process?
CL: It was highly iterative, which is largely thanks to the fact that the design is 3D-printed. We went through dozens of revisions, always looping in feedback from the audiophile community as we did so. We made quite a few posts on Reddit as we developed the headphones, and the amazing feedback that we got had a massive impact on the final kit.
What are your backgrounds?
CL: Both of us (Colin and Phil) have university degrees in computer and electrical engineering. We also have a wide array of industry experience in engineering, from medical devices to automotive to financial services and more. We've also been running our current company for about four years, focusing on open-source computer mice and trackballs.
Figure 4: Raspberry Pi Pico
How are you using the Pi Pico and RP2040 in the project?
CL: A small board sits between the Headphones and the computer. It's powered with an RP2040. It does the heavy lifting of the digital signal processing to shape the audio output. This requires a lot of floating point math computation, which is problematic because the RP2040 doesn't have a floating point unit. We got around this by utilizing the RP2040's other features, such as its dual-core design, the DMA (Direct Memory Access) unit, and the PIO (Programmable Input/Output). It might not seem like it, but the RP2040 punches way above its weight in the math computation area, even though it doesn't natively compute floating point numbers. We exceeded a DSP data rate of 4.6Mbps, which is impressive for a chip with no FPU.
Figure 5: Raspberry Pi RP2040
What made you go with the Pi Pico?
CL: The biggest reason we went with the Pico was because of the non-proprietary development environment surrounding the Pico. Many other chips require buying in to costly development toolchains, but the Pico doesn't. That's enabled all sorts of great things, such as CircuitPython and MicroPython, but also projects like ours. It's very easy - and free - to jump right in.
What additional features are you planning to add?
CL: We'll eventually add a microphone, closed backs for better sound isolation, noise-cancellation features, and self-calibration, to name just a few. It's an evolving process.
For more information on the Ploopy Headphones, head over to Ploopy’s website.
