The bars of a marimba work on the fundamental principal of a vibrating bar with two free ends: when some action, such as the impact of a mallet, sets such a bar into movement, it bends transversely, as in Figure 1. As long as the bar is vibrating in this manner, it produces a sound. However, through the workings of internal friction, the bar eventually comes to rest again, returning to its original, steady state.
Figure 1: Vibrating bar with two free ends
Figure 1 depicts the manner in which a bar with two free ends vibrates in its first mode. This mode of vibration dictates the pitch one hears when a bar is struck, known as the fundamental. However, a resonating bar will exhibit many different modes of vibration, all of which, sounding at different frequencies, are combined by the human ear in a process called fusion. The end result of this phenomenon is the perception of a pitch with character, or timbre. The first seven modes (corresponding to the fundamental and first six overtones) contributing to the pitch and timbre of a marimba bar are shown in Figure 2 on the next page.