Marimbas and bar percussion are undoubtedly complicated instruments.  Not only do the individual parts need to be precisely designed and built, but they all need to fit precisely within the confines of the overall instrument.  Then there's the bar / resonator tuning component.  This leads to the acoustical alignment of the bars precisely positioned over their individual resonator openings.  Finally, the job of the frame is to maintain the positioning of all components during play without any shifting. 

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