These PVC tubes are cut according to the Pythagorean ratios to produce the standard octave scale. You may put your ear close to the tubes to hear the dominant mode or you may blow across the top to excite the mode. Finally you can hit the end of the tubes with fingers or cupped hands to produce different quality notes. It is possible to play two octaves by changing the boundary conditions. Bringing your hand down on the tube end and holding it there produces a note an octave lower than hitting the end and bringing your hand up. It cost me $50 and a few hours to make.