Material is ground away from underside of the bars in an arch shape to lower the pitch. This allows the lower-pitched bars to be a manageable length. It is also the key to the "mellow" sound of the vibraphone (and marimba, which uses the same deep arch) compared with the brighter xylophone, which uses a shallower arch, and the glockenspiel, which has no arch at all. These rectangular bars have three primary modes of vibration. The deep arch causes these modes to align and create a consonant arrangement of intervals: a fundamental pitch, a pitch two octaves above that, and a third pitch an octave and a major third above the second. For the F3 bar that usually forms the lowest note on a vibraphone, there would be F3 as the fundamental, F5 as the first overtone and A6 as the second overtone. As a side effect, the arch causes the nodal points of the fundamental vibration to shift closer towards the ends of the bar.