“Rumba box” is a name used in the English-speaking Caribbean for bass kalimbas. Typically in these instruments the player sits on the box, reaching down between his or her legs to pluck the prongs. I’ve made several non-traditional variants, one of which is shown here. Most are chromatic, with prongs made of spring-tempered steel rods. On most of them the prongs have been reshaped to adjust the tuning of the most prominent overtone relative to the fundamental, making a more coherent tone quality. Some have rattles on the prongs. The rattles bring out the re-tuned overtone and give a distinctive edge to the tone.
The first instrument heard in the audio clip is a rumba box with rattles. It’s followed by very large rumba box accompanied by percussion and winds.