It is a self powered mini speaker system made with packaging cardboard. The bcardboard thickness was 6 mm and with proper pasting and ribs, i got a rigid mini box. Due to high damping property of packaging cardboard, i got a good quality sound output.
Basically i made this in 2006 for my SE k750i phone, even today it is working nicely. It gives a warm tube-like sound with emphasis on vocals and satisfactory high tones.