The system is built up of individual knock boxes.

Each box has its own memory and is completely self-contained. As you tap on the top of a box, the box waits for a few seconds and then taps back what it has heard. If you want more you add another box, and another, and another, tap, tap, tap.

Stacking the boxes creates longer and more complex rhythm lines as the patterns tumble down the resulting pyramids.

TapTap von Andy Huntington und Louise W. Klinker

(via de:bug blog)