Chartoni: my corrugated cardboard hifi speakers

A while ago Jan Wessel Hovingh gave me a Raspberry Pi Zero as a thank you gift for a talk I gave at the University of Applied Sciences in Leeuwarden. I decided to create my own streaming audio speakers with this Pi. After quite a bit of DuckDuckGoing, quite some help from many wonderful people and some work it’s done: two hifi speakers made out of layers of corrugated card board, powered by a Raspberry Pi.

The speakers

The design of the speakers is a mashup of two designs by Tony Gee of Humble Home Made Hifi. The choice of drivers and the dimensions of the box are based on the DD8-MkII. Inspired by the design of the Otello I moved the bass reflex port to the front. I like this asymmetrical layout better. I ordered the crossover filters from Humble Home Made Hifi.

The box

The box is made out of about 80 layers of 4.5mm thick high quality corrugated cardboard, glued together with common wood glue. Yes, there is such a thing as high quality card board. I ordered mine at the wonderful and very helpful Jansen-Wijsmuller & Beuns, Wholesale of bookbinders, restoration and conservation materials. The insides of the speakers are covered with CTK Vibrodamping. I used one of the lasercutters we have at our university to cut everything into its exact shape. If you need it, you can download all the EPS files right here. I created these by hand. Later on I learned that there’s software that can do this for you …

The amp

There are a few sounds cards for the Raspberry Pi Zero that convert digital stuff to analog sound, like the Allo Miniboss. Instead of buying this Miniboss and sticking to the plan I bought a new Raspberry Pi 3 with a Dion Audio LOCO DAC-AMP.

I tried a few different software distributions to run on the Pi. I really liked Moode Audio. Lots of features in an easy enough web interface. But in the end I couldn’t get it to work for my set up. So now everything runs on a simple Raspbian Stretch Lite with only the incredible Shairport-Sync installed, since Airplay is the only way we stream music. I tweaked the Shairport-Sync settings a little bit. For higher quality sound I turned on interpolation = "soxr", I set output_rate = 44100 and output_format = "S32". I tried higher numbers for the output_rate but the Pi couldn’t handle these, and I can’t hear the difference anyway. I also set allow_session_interruption = "yes" so we can intervene if someone else is playing annoying music. And I called the Airport network Χαρτόνι, which means cardboard in Greek.

The case

I had some cardboard left so I designed and built a case for the LOCO as well. The idea was that diagonals would allow for bigger openings so the Pi will be able to get rid of the heat, while it stays a bit dust free. I’m not sure about the dust, but the heat is definitely fine. When idle the temperature is around 44°C, and it doesn’t get over 50°C when we play music. The EPS for this case can be found in this zip as well.

Thank you

I want to thank Dave Krooshof for helping me out with about everything in this project. Without him I would not have been able to make this thing. And thank you to Jeanet Verwoerd from Jansen-Wijsmuller & Beuns who kept helping me patiently with my impossible questions. Also big thank you to Tony Gee of Humble Home Made Hifi who didn’t laugh at the idea of building cardboard speakers, and who later answered all kinds of questions via email. And of course for sharing his wonderful designs. Thank you as well to Miquel Blauw of Dion Audio who answered all my emails and really helped me out in many different ways. And of course a huge thank you to all the people of the internet who share their knowledge about all the extremely nerdy stuff I needed on their blogs, on github and on all kinds of fora.

And now I still have this Raspberry Pi Zero.