To sound these aluminum rods, the player presses and releases the spring-mounted hammers at the bottom. This activates the longitudinal mode of vibration in the rods. It also inevitably excites transverse modes as well. The transverse modes produce a somewhat discordant clang at the start of the tone which quickly disappears, revealing the clear, very high-pitched, long-sustaining tone of the longitudinal mode. 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. Because the waves travel fast in aluminum (much faster than in air), the resulting pitches are very high. Lower pitches would require very long rods.