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Can we tell the difference in the measured acoustic proper- ties of instruments of such vastly different prices? Can we discover the acoustic secret, if any, of the old Cremonese master violins? Can a knowledge and understanding of the acoustical properties of the old violins help modern makers match the sounds of such violins? These are the major chal- lenges for acousticians.
Despite the continuing reluctance of many violin makers to accept the intrusion of science into the traditional art of vio- lin making, it is surely no coincidence that outstanding mak- ers like Zygmuntowicz and Curtin have also played promi- nent roles in advancing our knowledge and understanding of the sounds of fine Italian instruments and their acoustic properties.
Today, as a result of strong collaborations involving violin makers, museum curators, players, owners, dealers, and ac- ousticians, we have a wealth of information on the acousti- cal properties of nearly 100 classic Italian violins including many Stradivari and Guarneri violins, as well as many fine modern instruments, important knowledge that was miss- ing until the last few years.
Such information establishes a “benchmark” for modern makers, if their instruments are to consistently match the sounds of the early Cremonese makers. Simple acoustic measurements in their workshops during the making of their instruments can help them achieve this.
Interestingly, Claudia Fritz and her collaborators (Fritz et al., 2014) recently conducted a rigorously designed psycho- acoustic investigation of six fine Italian and six modern vio- lins, which involved comparative listening tests and parallel vibroacoustic characterization. The outcome was that with- out visual clues even top international soloists were unable to reliably distinguish the old instruments from the new de- spite their huge disparity in value. This confirmed similar conclusions from a previous investigation involving a small- er number of instruments (Fritz et al., 2012).
The concept of a “Stradivari secret” known only to the clas- sic Italian makers to account for the outstanding sound of many of their instruments is now largely discredited, not in the least because the sound of the instruments we listen to today are very different from when they were originally made. This is because they were “modernized” in various subtle ways in the 19th century by the use of metal-covered rather than pure-gut strings, a lengthened neck, a different standard tuning pitch, a modern bridge, and being played
with a modern bow. This was in response to the need for instruments that could respond to the increasingly virtuosic demands of the player and project strongly over the sound of the larger orchestras and concert halls of the day.
Radiated Sound
In many ways, the acoustics of the violin is closely analo- gous to that of a loudspeaker mounted in a bass-reflex cabi- net enclosure as described in many acoustics textbooks (e.g., Kinsler et al., 1982). The thin-walled body shell of the vio- lin radiates sound directly just like a loudspeaker cone. The shell vibrations also produce pressure fluctuations inside the hollow body, which excite the Helmholtz f-hole resonance, the highly localized flow of air bouncing in and out of the f-holes cut in the top plate. The Helmholtz resonance fre- quency is determined by the size and geometry of the f-holes and compressibility of the air inside the body shell. This is similar to the induced vibrations of air through the open hole in a bass-reflex loudspeaker cabinet. In both cases, this significantly boosts the sound radiated at low frequencies, where radiation from the higher frequency body shell or loudspeaker cone resonances would otherwise have fallen off very rapidly.
Contrary to what many players believe, negligible sound is radiated by the vibrating string because its diameter is much smaller than the acoustic wavelength at all audio fre- quencies of interest. Nevertheless, the bowed string clearly provides the important driving force producing the sound of the instrument just like the electrical current exciting a loudspeaker cone. The quality of the radiated sound is there- fore only as good as the player controlling the quality of the bowed string input!
Sound is excited by transverse “Helmholtz” bowed-string waves excited on the string, which exert a force with a saw- tooth waveform on the supporting bridge as described be- low. Because of the offset soundpost wedged between the top and back plates, the transverse bowed-string forces the bridge to bounce up and down and rock asymmetrically backward and forward in its own plane on the island area between the f-holes cut into the top plate, as illustrated in Figure 2. The bridge and island area act as an acoustic trans- former coupling energy from the vibrating string into the vibrating modes of the lower and upper bouts of both the top and back plates of the body shell.
The radiated sound is then strongly dependent on the coupling of the vibrating strings to the radiating
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