To sound these aluminum rods, the player strokes them lengthwise with rosined fingers or high-traction rubber gloves. This excites the longitudinal mode of vibration in the rods. The tones don’t start all at once; they develop gradually with continued stroking. Once they get going they can really sing, producing high-pitched, long-sustaining tones, potentially quite loud. The longitudinal mode involves wave fronts reflecting back and forth along the length of the rods, much as in the air columns of wind instruments. The pitches are high because the waves travel fast in aluminum (much faster than in air). Lower pitches would require very long rods.