Materials in Musical Instruments: Romance of Art and Science
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MRS BULLETIN/MARCH 1995
wind instruments. The most significant resonances for these instruments are associated with standing waves in air columns, rather than the structural vibrations in the body.6 The material from which such an instrument is constructed, along with the skill of the instrument maker to produce a precision instrument, certainly affects the "feel" of the instrument sensed by the musician, and this in turn is reflected in the performer's ability to move the audience. Furthermore, the operation of pitchcontrol mechanisms affects the ease of playing, and again, materials choices play a significant role. Musical instruments represent a delicate interplay of many elements.7 For each of these elements, materials often influence the quality of the sound produced. Consider the violin. The slip-stick action caused by the movement of the bow hair across the string initiates the string vibration. The number of possible frequencies is limited by imposing nearly fixed boundary conditions at the nut and the bridge. They are determined by the length of the string between the terminal points in addition to the tension and the linear mass density. These vibrations are transmitted to the violin body by the bridge. The response of the body depends on several factors, many of which are related to the physical characteristics of the material used in the plates, as well as the geometric shape, mass distribution, and nature of the support at the boundaries. The material routinely used for the top plate of a violin is Norway spruce. This wood is highly anisotropic, with significantly different elastic constants in the three principal directions. A major problem with natural
wood is that trees with consistently similar densities and stiffness properties are very difficult to find. If a synthetic material could be produced with the desired anisotropy in elastic properties, along with the appropriate density and stiffness, it could be used as a consistent resource for instrument making. Researchers in France have used laminated synthetic materials to produce a violin of remarkable tone quality. Other efforts to utilize manufactured materials in musical instruments include graphite-epoxy guitar bodies and synthetic piano soundboards. The use of Kelon in place of Honduran rosewood in marimba bars has already become widespread. Several good reasons, other than the dwindling supply of natural resources, can be given for using synthetic materials in musical instruments. One such example is the use of plastics in drumheads. Generally, animal skins, while still in use in some applications, exhibit properties of strong sensitivity to temperature and humidity change, a fact which creates problems in some settings, such as on a concert stage where the temperature rise induced by stage lights can cause noticeable tuning problems. Modern manufacturing technology also enables production of plastic membranes with consistent thickness control, which in turn simplifies routine tympani tuning. Another example of the departure from traditio
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