THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

18.9 Strings 533acoustical asymmetry inside the body. The shape, positioning, wood quality, andfitting of the sound post constitute highly critical factors in performance qualityof the instrument.The bass bar runs along the length of the interior surface of the top plate approximatelyunder the lowest-tuned string. Its function is to keep the vibrations of theupper and lower areas of the top plate in phase with the left foot of the bridge. Thebar is glued to the top plate in such a manner so as to provide structural strength tothe thin wood forming the top plate. Both the sound post and the bass bar enable thetop plate to withstand downward forces of 70–90 N from the strings. The contourof the bass bar is extremely important in the proper “thinning” or “tuning” of thetop plate.The f-holes serves two acoustical purposes: (a) reduction of the stiffness of thesurface on which the bridge stands in order to provide suitably tapered transitionbetween the bridge and the radiating area of the top plate and (b) formation of aHelmholtz resonator with the body of the instrument, thereby strengthening soundin the lowest octaves. The purling are inlays of thin wood placed in grooves alongthe edges of the plates. This allows the plates to vibrate more as if they were hingedrather than being clamped at the edges.In the violin, the top plate is generally constructed of softer Norway spruce(Picco abies or Picca excelsis), and back plate and the ribs are carved from (harder)curly maple (Acer platanoides). Fingerboard, tailpiece, and pegs are usually madeof ebony. The bow stick is made from pernambuco.The strings of the violin were originally all gut. Since about the seventiethcentury, the lowest (G) string was commonly wound with silver to improve theresponse. Present-day violinists use wound strings (i.e., metal wound over coresof gut, nylon, or metal) for D and A strings and steel E-string. The latter string canbe finely adjusted with the use of a fine tuner.In addition to the four principal members of the violin family, the aforementionedCatgut Acoustical Society was responsible for the development of the violin octet,an ensemble of eight specially scaled new violin family instruments (Hutchins,1967). The octet of instruments, illustrated in the photograph of Figure 18.20 anddeveloped by the society to meet the challenge of encompassing the entire rangeif orchestral music, consists of the treble violin, the soprano violin, the mezzoviolin, the alto violin, the tenor violin, the baritone violin, the small bass, and thecontrabass. Although these instruments form a family with basic traits in common,each member has its own individual personality. The homogeneity of sound arisesfrom adjustments in body length and other physical characteristics so that eachinstrument has its own main wood resonance and main air resonance near the twoopen middle strings. The musical ranges of the strings on these instruments areshown in Figure 18.21, as they relate to the corresponding notes on a standardpiano. These eight instruments of the new violin family range in overall lengthfrom 48 cm to 214 cm.The principal modern struck-string instrument is the piano that are availablein several models, ranging in size from the more modest upright or spinet pianoto the concert grand piano. The heart of the piano consists of a large number of