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Marimbas and Other Bar Percussion Instruments There is nothing that cannot be classified into some family. Marimbas and other bar percussion instruments are, using one classification system, idiophones. Then, within the bar percussion instruments are marimbas, xylophones, and vibraphones. Not always agreed upon, but in general, a marimba usually has a wooden bar or a bar made of some man-made material which has the characteristics of wood. Rosewood or certain man-made materials seem to be the agreed upon optimum. When a marimba bar is struck it will produce not only the fundamental note but also some other notes which may be called partials. Some say that the ideal partials for a marimba are 4:1 octaves above the fundamental and 10:1 above. A 4:1 would be the musical note two octaves above the fundamental. 10:1 would be three octaves and a major third above the fundamental. A xylophone often has rosewood or wooden bars as well. But, the partials are 3:1 and 6:1 above the fundamental. This would be one octave and a perfect fifth and two octaves and a perfect fifth above the fundamental. The vibe usually has metal (aluminum) bars but has the same partials as a marimba. Marimba and vibe bars usually have a deep arch and are further tuned for the fundamental note at each end of the arch. Xylophone bars have a shallow arch.
Resonators are then added beneath the bar to reinforce the sound made when the bar is struck. I built a marimba of over 3.5 octaves. The case was built of walnut, the bars are a mix of Honduran rosewood, Brazilian rosewood, and orange osage. The resonators are made from salvaged hollow-core doors and are therefore, as you can see in the picture, rectangular in shape. Note, in the illustration, that the holes for the nodal points (the fundamental node) are at 22.4% of the bar if there is no undercut. The undercut, in a sense, lengthens the bar and thus a highly accurate placement of the holes would be a bit further. It is my understanding that during wartimes when metal was in short supply, resonators were even made from paper tubes. I tried PVC, aluminum, steel, and paper. I did not discern any differences nor did others who sampled the various trials. It would seem that the resonators
would provide amplification aside from the bouncing of the soundwave back up. One can
easily feel the resonators vibrate. I tuned most of the resonators by striking the
side and using a tuning meter. Only the shorter, higher frequency resonators did not lend
themselves to this technique. Also, note that the resonators actually do not run from long
to short and then to long again. This a merely a cosmetic step. The higher frequency
resonators, although long, are actually blocked up toward the end nearest the bar. In
actuality the tube may be stopped less than one inch from the top. In general, people probably prefer a consistent color and wood type for the bars. Because the bars I used were both salvaged and also made by me the various woods were used. I find the contrasts in wood appealing. An experienced ear would probably find a difference in complex tone qualities and, of course, that would be undesirable. For me, I hear no difference and the variety of woods is interesting and attractive. Making quality tuned bars is probably beyond the capability of an amateur. I have some bars that sound good and some that could use improvement. The basics of tuning bars is: removal of wood from the underside lowers the frequency. Wood removed from the end of the wooden bar raises the frequency. Below are a few links which will provide you with more information about marimbas and other bar percussion instruments Bart Hopikins, a writer of many fine books on made instruments Greg Merrill on Construction of Marimba (excellent) To return click below Family Room Home Library-Genealogy Music Room Garage-wheels Attic-Misc. |
The illustration at the left tells
something about tuning the bars.