The acoustic complexity of keyboard percussion instruments. Part I: (What we know and what we wish we knew) Leigh Howard Stevens
Leigh H. Stevens · The Journal of the Acoustical Society of America · 2015
Part I Introduction to tuned bars and resonators Keyboard Percussion Instruments include innumerable variations of marimbas, xylophones, vibraphones, and glockenspiels. The tone bars, made of wood, metal, or other materials, are often incapable of producing sufficient volume without the amplifying assistance of a resonating tube or chamber. Unfortunately, these two vibrating systems (bar and resonator) react in opposite directions to changes in temperature, decoupling from their ideal relationship with any rise or fall in temperature. Also, unlike string, brass, or woodwind instruments, where the overtones are produced “naturally” and “are what they are,” the overtones of the bars of keyboard percussion instruments can be manipulated and controlled in the design and manufacturing process. For example, while both instruments have tone bars made of rosewood, the xylophone has the second partial tuned to an octave and a perfect fifth above the fundamental, while a marimba has the second partial tuned to a frequency two octaves above the fundamental. While we can identify and lower the frequency of many of the prominent partials contained in tone bars, their interdependence within the bar, and their coupling with a resonator provides a level of complexity for the designer and manufacturer, perhaps unrivaled in musical instrument manufacturing.