Ultrasonic vibrations

Some preliminary studies have shown scientifically the richness of the sound of a silk string qin. The metal string sound, though perhaps stronger, seems much less rich. Although the difference in sound can be studied scientically, value judgements on the results remain subjective. However, metal strings may damage old qins. Here the question of whether ultrasonic vibrations can actually cause physical damage is perhaps most crucial.

Some years ago in Geneva, Georges Goormaghtigh, a strong advocate for the aesthetic value of the silk string guqin sound, introduced me to luthier Luc Breton,¹ who similarly advocates gut strings on early violins, which he also makes. Because of Georges, Luc became interested in guqins, and together they constructed one. Since then Luc has done repairs on Georges' old guqins as well as on one of my own (he did a very good job).

Luc believes that metal strings can cause damage to string instruments. This is not just because, to produce the same pitch, metal strings put an instrument under greater tension than do gut strings of the same gauge, but also because metal strings produce possibly harmful ultrasonic vibrations.

Can ultrasonic vibrations from metal strings actually cause damage to the wood structure of musical instruments? People who use and/or make metal strings on stringed instruments do not believe that vibrations can cause such damage, but this opinion is not universally shared. The subject thus requires further scientific testing.

The basic hypothesis is that sounds produced by metal strings can include ultrasonic vibrations that are not produced by less dense materials such as gut, nylon or silk. Biology laboratories currently use sonicating machines to create ultrasounds that will break up cells. Such ultrasound frequencies are certainly different from those produced by music instruments, so one must devise specific tests to determine whether vibrations from metal strings can cause damage to the wood structure.

In 1995, at the University of Lausanne, Switzerland, Luc participated in a student project designed to see if some ultrasonic damage could be produced and then observed microscopically. Dr. Pierre Vollenweider was responsible for the mentioned student work. Dr. Vollenweider is a plant anatomist and forest ecologist whose present address is the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL).

In July 2002 I asked Pierre about this study, specifically requesting permission to include photos that they took (I have seen three). He wrote to me the following:

"In the course of our research at WSL we sometimes use electronically generated ultrasound to break up plant or bacteria cells.

"It seems established that metal strings can also produce ultrasonic sounds, so when a music instrument is played several hours a day over a period of years, an effect on wood structure can be hypothesized. However, as far as I know this has never been studied scientifically. Thus, scientific arguments have not yet been produced documenting a damaging effect by metal strings on the wood of musical instruments.

"In the 1995 student project at the University of Lausanne we tried to mimic some of the possible effects of the vibrations of metal strings on the cellular structure of the wood in stringed instruments. To do this we subjected wood block samples (spruce) to ultrasonic sounds using a sonicating machine used, for example, to break up bacteria cells to extract the cell material.

"Some cellular damage to the wood can be seen in micro-photographs. However, because we were not using the actual materials (wood or strings) of a music instrument, and because this was a quickly-done student work, we dont know how far these artificial damages are similar to those possibly produced by metal strings, if any. We considered it only preliminary research and did not publish the results. Likewise, the photos should not be published because they might be misinterpreted or misused.

"I do think that this subject as well as others touching wood quality and its importance for building musical instruments is ripe for a research project. The effects of metal strings together with other factors potentially influencing the wood structure and wood quality still divide music instrument makers.

"Although my main research is on other aspects of plant anatomy, I would much appreciate being informed and if possible consulted concerning the use of the pictures we did once. I can probably best advise about what they say exactly. For sure they do not prove the negative effects of metal strings on the wood structure of musical instruments. They show only something already known: ultrasounds can be harmful to biological material. They also suggest that apparent damage by ultrasonic sounds on a wood element can be viewed with microscopic methods; these methods, alas, are destructive.

"I think that this is an exciting research field and I much appreciate it when I hear about persons who get interested. I hope that you will continue and wish you success."

After this the École Polytechnique of Lausanne, within a wider research project on dendrology (study of trees), carried out further research on this damage. I have not yet seen the publication of their results, only mention of it in an article by Philippe Borer dated 2002 entitled Paganini's Strings (Le Corde di Paganini) and attached here.² Of particular note is Borer's concluding remarks, directly addressing the issue of strings from an aesthetic and indeed cosmological rather than scientific viewpoint:

From the point of view of the ancient makers, the violin was constructed around the strings and for the strings and not the reverse. Every step in their construction was performed with reference to the string. For violin makers in those days the string was more than just a simple accessory, rather, it was the basic starting element, the generating essence of sound. I hope that this brief exposé of facts related to string instruments may point to the need to give an instrument such as Niccolò Paganini’s Guarneri ‘del Gesù’ the best and most appropriate strings.

How much more clearly true for an instrument such as the guqin, a highly honored cultural heirloom since ancient times referred to by the appellation "silk and wood"?

Return to silk strings, or to the Guqin ToC.

Footnotes (Shorthand references are explained on a separate page)

1. Luc Breton
Luc is a luthier in Vaux-sur-Morges, Switzerland, who specializes in making and repairing violins. However, under the instruction of Georges Goormaghtigh he made a guqin, thus learning to do repairs on them.
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2. Paganini's Strings
Thanks to Jun Keller, a violinist with the Vienna Philharmonic Orchestra, for sending me a copy of this article,
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