Construction of the orchestra xylophone
Rather than describe the many different types of xylophone that have appeared all over the world in the course of history, we will restrict ourselves here to a detailed description of the modern orchestra xylophone only.
The frame on which the bars are mounted rests on a metal stand, which has wheels for ease of transport. This is necessary because percussion instruments often have to move to a different position.
The modern orchestra xylophone has chromatically tuned bars, which are arranged in two rows in the same way as the keys of a piano. The row of bars which corresponds to the piano’s black keys is slightly elevated. Nowadays the bars have holes drilled at their nodal points through which a string is threaded on which the bars are suspended. Each bar is separated from its neighbor by pegs, so that it hangs and can vibrate freely.
On older xylophones or other types of xylophone (trough xylophone, Orff Method xylophones) the bars rest on a pad of felt or rubber.
The number of bars varies according to the instrument’s range, which is virtually impossible to define. The average range of modern orchestra xylophones can lie anywhere between three (C5–C8), three and a half (F4–C8) and four octaves (C4–C8). Most orchestras use several xylophones, one of which has a range of four octaves. Five-octave instruments failed to gain acceptance due to the inferiority of the sound, although parts have been written for them.
The pitch of each bar is determined by its length, thickness and the density of the material; the width has no influence on pitch. The longer, thinner and denser the bar the lower the pitch. The shorter, thicker and less dense the bar, the higher the pitch. The bars can be tuned by adding or taking away material.
When tuning, the following rule applies: if material is filed off the ends of the bar, the pitch of the fundamental note is raised. If, on the other hand, material is carved out of the center of the bar (either from the top or the bottom), thus making it thinner, the pitch of the fundamental note is lowered. By removing material from different parts of the bar it is even possible to tune single partials. If it is necessary to improve the tuning quickly, the fundamental note can be raised by adding lumps of wax, a practice common on African xylophones.
Unlike vibrating strings, halving the length of a bar raises its pitch by two octaves. It is for this reason that the difference in length between the lowest and the highest bar is relatively small. A xylophone’s bars are between roughly 2.5 cm and 4.6 cm wide, between 1.5 cm and 2.5 cm thick and between roughly 38 cm (lowest note) and 13.5 cm (highest note) long.
Modern orchestra xylophones are generally tuned to 442 hertz equal temperament. However, xylophone makers produce instruments in various tunings, because of the differences in tuning pitch used by orchestras in different parts of the world.
Unlike earlier models, modern orchestra xylophones are equipped with resonator tubes on the underside. Each bar has its own resonator. The resonators serve to amplify the sound and soften the tone somewhat; xylophones with no resonators, common in the 19th and early 20th centuries in orchestral music, had a harder timbre.
Which wood should be used for the bars?
Every type of wood has a particular timbre; soft woods such as alder and poplar have a softer, more gentle sound.
Very hard woods such as maple, or exotic woods such as Honduras or Brazilian rosewood have a sound which is richer in partials and more resonant. They sound brighter than soft woods.
On modern orchestra xylophones very hard and usually exotic woods such as Honduras rosewood, Japanese birch or Burmese padouk are used. Softer woods are preferred on children’s instruments. When choosing wood for a musical instrument it is very important that it should be evenly matured, because it is only in wood with this quality that a sound rich in partials can develop. The sound is also influenced by the way the bars are finished; depending on how they are carved, which is usually on the underside, either the fundamental tone (= 1st partial) or a higher partial can be made more prominent.
Xylophone bars are often tuned in such a way that the 3rd partial (= octave + a fifth above the pitch of the fundamental) is more prominent, whereas on marimbas this is more often case for the 2nd partial (= octave above the fundamental). However, on xylophones it is also usual to enhance the 1st partial (= fundamental tone), which softens the timbre.
Wood is very susceptible to changes in the environment and is therefore less capable of maintaining a tuning than synthetic materials. The quality of its sound, however, is far superior. Touring musicians prefer to use synthetic bars. Instruments with synthetic bars are of course still called xylophones (= wood sounder).