Made to go places: lightweight thin-walled enclosure

Made to go places: lightweight thin-walled enclosure

The world of audio technology is the story of hard-won advancements, especially in the realm of loudspeaker design. Over the decades, designs come and go, but one constant remains: the collaborative spirit and the "folk process" fueling innovation. Loudspeaker makers have learned from each other's designs to push the boundaries of what's possible, sometimes building on designs that have entered the public domain, sometimes reinventing solutions independently.

Open Source Boombox Project

MAKEBOOMBOXES Embodies the Spirit of Shared Innovation

Recently, we decided to open-source our latest design, the MOJOFESTO DIY boombox, inviting the global community to join us in redefining the limits of how great a home-made portable speaker kit can be. This decision was not just about transparency but was also a nod to the collaborative efforts that have historically propelled forward the qualities of loudspeakers and musical instruments generally.

The design journey of the MOJOFESTO has been particularly reliant on community -- the feedback of many friends and colleagues, testing in public and asking for a lot of advice from generous inventors who loved the basic idea. And above all we had a lot of fun trying and failing, learning from many fits and starts.

Because boomboxes are portable audio, we needed a thin-walled, lightweight enclosure. But the high pressures kept slapping the back wall of the box making unpleasant thuds and quacks. After exploring many ways of trying to stiffen the back wall, we pivoted, welcoming and tuning thin-walled vibration instead of bracing against it. Having built guitars in college, this "acoustic guitar-body-like" approach was a natural path.

Accidental Re-discovery of a BBC Legendary Sound 

By opening up and controlling free vibration of all surfaces of the box, we unintentionally echoed some of the principles of the legendary BBC LS3/5 speakers (we later came to understand). Although I've only read about these iconic models and their "BBC thinwall" tradition, and I've yet to hear them in person, the similarities in design philosophy are right there.

The BBC LS3/5 speaker utilized very thin-walls as opposed to thick heavy plywood so commonplace in speaker cabinets prior and largely to this day. They originally featured 9mm birch plywood walls, which were later thickened to 12mm to enhance acoustics. The LS3/5s solved the need for more lightweight enclosures much easier to move around the BBC studios for rapid reconfiguration and room sound optimizaton. While their thin walls reduced weight drastically, it also gave them their distinctive midrange clarity. 

Same Goal, Related Design Solutions

Our MOJOFESTO design uses even thinner 3mm hardboard or wood-veneered MDF such as Mahogany and Walnut on the sides and back, and 5mm Cedar plywood for the front soundboard with strategic Birch ply reinforcement stiffening the driver mounts. Embracing these flexible, strong, resonant natural materials creates a rich, immersive sound experience at an even lighter weight.

In contrast to the LS3/5 speakers being heavily damped internally to deepen the bass response frequency, we introduced an innovative bass-enhancing feature: an f-hole-inspired floating relief in the back wall. This design allows the entire rear surface of the speaker to deflect harmonically without unpleasant thumps and peaks -- much like a passive radiator provides a low-pass filtering boundary but instead of pistonic large movement, the small linear displacement spread over the large backboard surface delivers clarity and depth in the bass.

Innovating the Future of Sound -- Openly 

And all this design evolution we want to share with you, music lovers who can hear the difference, and speaker makers who can maybe make use of these inventions. Our open-source offering and venture is not just about sharing a product but about inviting feedback, experimentation, and further innovation. By revealing our design and the thinking it embodies, we hope to inspire both amateur and professional audio enthusiasts to experiment, tweak, and inevitably improve upon our core design.

The potential for collective advancement in speaker technology is what excites us about sharing our designs. With this invitation we hope to set the stage for onoing breakthroughs and democratization in the art of audio technology.

See my Tech Talk on the origins and design of the MOJOFESTO I gave at Circuit Launch in Oakland, where I laser cut the parts for the DIY kits.

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