More on Tuning bass Marimba Bars
My current theory is that a triple tuned bar is a happy bar. Notice the pitch of any resonate bar shaped piece of wood (with no arch cut). There is the dominant pitch and a prominent overtone approximately a tenth above it. The fundamental pitch of a marimba bar is created by the interaction of the flexibility of the center of the bar and the weight of the ends of the bar. The ends of the bar also function somewhat independently as their own selves, and can be tuned to two octaves above the fundamental and also the tenth above themselves. This is really what the bar wants to do. Tuning the bar is helping it attain this state. If you have tuned some bars you know that changing any of these variables (flexibility at the center, weight and length of the ends) changes the others also. So removing wood from the center to increase the flexibility will also slightly decrease the weight of the ends. This mostly lowers the fundamental, slightly lowers the two octave overtone and may barely change the tenth tone also. Removing wood from the ends of the arch shortens and lightens the "end bars" lowering the two octave and tenth overtone pitches and possibly even raising the fundamental. As these three pitches get closer to in tune with each other, they reinforce each other's action in the bar. Consequently they produce more of the organized air pressure variations we recognize as pitch.