No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Effects of Continuous Vibration on Dynamic Viscoelasticity of Wood
Abstract
The effects of the continuous vibration of small amplitude on the dynamic viscoelasticity of wood were studied for seven kinds of species of softwood and hardwood. The free-free flexural vibration method of rectangular beams was used. The vibration test was made in a chamber in which the temperature and humidity was controlled at 20°C and 65% R.H.The vibration was continued for five hours by using a self running oscillation circuit which automatically regulated a resonance frequency of a vibration system. The resonance frequency ranged from 100 to 170Hz and the amplitude of the vibration was 0.14mm at the end of a specimen. The dynamic Young's modulus E' and the loss tangent tanδ were measured at each one hour interval at ten degrees of amplitude in the range from 0.015 to 0.40mm.The dynamic Young's modulus was not affected by the subjected continuous vibration. On the other hand, the loss tangent decreased until about one or two hours and approached gradually to a constant value as increase of the vibration time. After five hours, the loss tangent decreased by about 5 to 15%.The loss-tangent decreasing process was studied by using the rate process theory, and the qualitative trend of the experiments could be well explained.
... Among the numerous factors that influence the quality of an acoustical musical instrument, the material property viscoelasticity (often referred to as damping) in the audio frequency range (20 Hz to 20 kHz) has been determined to have an important role in a number of studies [1], including recent experiments in composite design [2]. Moreover, viscoelasticity seems to vary during the playing time [3] and according to the moisture content [4]. This experience provided more motivation for the experiments reported here. ...
... Finally, the variation of the loss angle was a decrease of 5%. Sobue [3] had proposed molecular rearrangement to explain the behavior of the loss tangent with respect to vibration run. It is possible that the vibration could deliver enough energy to break links between water molecules. ...
... A second set of experiments indicated that wood damping is dependent on exposure time to vibration (1 kHz) and humidity. These two results indicate the possible role of water molecules in viscoelasticity of wood-a hypothesis proposed by Sobue [3]. ...
The viscoelasticity (damping) property of spruce wood was measured for the audio frequency range 20 Hz to 20 kHz and as a function of time when vibrated at 1 kHz. After less than one hour of vibration, the loss tangent of the spruce decreased by 6%.
... Und ebenso wie alterungsbedingte Änderungen scheinen vibrationsbedingte Änderungen umkehrbar zu sein, wenn sich die Feuchtigkeit stark ändert. [11]. Möglicherweise liefern Vibrationen genügend Energie um die Verbindungen zwischen Wassermolekülen aufzubrechen, was zu geringerer interner Reibung führt [6]. ...
Zusammenfassung: Unter kontrollierten experimentellen Bedingungen konnte bisher keine subjektiv empfundene Klangverbesserung von Musikinstrumenten durch Einspielen nachgewiesen werden. Auch die bloße Unterscheidbarkeit zwischen viel und wenig gespielten Instrumenten misslang auf subjektiver Ebene. Spielabhängige Veränderungen in der Frequenzkurve können anscheinend messbar sein, wurden aber nicht in allen Untersuchungen gefunden. In diesem Artikel werden empirische Befunde zu natürlichem und künstlichem (maschinellem) Einspielen sowie verschiedene Erklärungsansätze für einen möglichen Einspieleffekt vorgestellt.
... Another theory [5] explains the playing-in effect through the slow displacing of water molecules away from areas under high strain to areas under low strain. A similar explanation assumes a molecular re-positioning [11]. Possibly the vibrations provide sufficient energy to break up the connections between the water molecules, which leads to less internal friction [6]. ...
Perceptual enhancement of the sound of musical instruments due to long-term playing has not been found yet in experiments under controlled conditions. Subjects were even unable to make a mere differentiation between much and less played instruments. Constant playing may lead to changes in the frequency curve, but are not found in all studies. This review article presents empirical findings concerning natural and artificial (mechanical) breaking-in. Different explanations for a possible breaking-in effect are discussed.
... It is therefore plausible that chemical or physical treatments may account for the different DSC profiles between Stradivari's violins and cellos, but different vibration frequencies may also be critical. Even a few hours of vibration has been shown to reduce the internal friction of wood, presumably by rearranging hydrogen bonds and polymer chains (31). Therefore, it is conceivable that high-frequency vibrations could have gradually altered the ultrastructure of wood fibers, acting in concert with hemicellulose decomposition over time. ...
Significance
There have been numerous attempts to elucidate the “secrets” of Stradivari violins, to explain why functional replacements have not been reproduced over the past two centuries. Whether there are systematic differences between Stradivari violins and later imitations has been heatedly debated. Our analysis of Stradivari’s maples from three independent sources showed reproducible differences in chemical compositions compared with modern maples. Stradivari’s use of mineral-treated maples belonged to a forgotten tradition unknown to later violin makers. His maple also appeared to be transformed by aging and vibration, resulting in a unique composite material unavailable to modern makers. Modern chemical analyses may, therefore, improve our understanding of Stradivari’s unique craft and inspire the development of novel material approaches in instrument making.
... Continuous vibration, on the other hand, has been reported several times to affect the vibrational properties of wood. Sobue and Okayasu found that the tanı of wood decreased exponentially with time under forced vibration , whereas the E' remained unchanged, irrespective of wood species [49]. A similar phenomenon was reported by Hunt and Balsan [50]. ...
The reversible and irreversible effects of natural and artificial hydrothermal ageing are reviewed with respect to the hygroscopicity and acoustic properties relevant to the practical quality of wooden musical instruments. Long-term natural ageing reduces the hygroscopicity of wood while improving its acoustic quality, but these changes are partly reversible by exposure to high humidity. Similar reversible changes are observed in hydrothermally treated wood, especially when the wood is heated at an intermediate relative humidity. These reversible changes are attributed to the annealing-like rearrangement of amorphous wood polymers or the temporary closure of micropores, but further investigation is necessary. Color change resulting from natural ageing is shown to be successfully reproducible by oven-heating.
... It is therefore plausible that chemical or physical treatments may account for the different DSC profiles between Stradivari's violins and cellos, but different vibration frequencies may also be critical. Even a few hours of vibration has been shown to reduce the internal friction of wood, presumably by rearranging hydrogen bonds and polymer chains (31). Therefore, it is conceivable that high-frequency vibrations could have gradually altered the ultrastructure of wood fibers, acting in concert with hemicellulose decomposition over time. ...
Violins made by Antonio Stradivari are renowned for having been the preferred instruments of many leading violinists for over two centuries. There have been long-standing questions about whether wood used by Stradivari possessed unique properties compared with modern tonewood for violin making. Analyses of maple samples removed from four Stradivari and a Guarneri instrument revealed highly distinct organic and inorganic compositions compared with modern maples. By solid-state ¹³C NMR spectroscopy, we observed that about one-third of hemicellulose had decomposed after three centuries, accompanied by signs of lignin oxidation. No apparent changes in cellulose were detected by NMR and synchrotron X-ray diffraction. By thermogravimetric analysis, historical maples exhibited reduced equilibrium moisture content. In differential scanning calorimetry measurements, only maples from Stradivari violins, but not his cellos, exhibited unusual thermooxidation patterns distinct from natural wood. Elemental analyses by inductively coupled plasma mass spectrometry suggested that Stradivari’s maples were treated with complex mineral preservatives containing Al, Ca, Cu, Na, K, and Zn. This type of chemical seasoning was an unusual practice, unknown to later generations of violin makers. In their current state, maples in Stradivari violins have very different chemical properties compared with their modern counterparts, likely due to the combined effects of aging, chemical treatments, and vibrations. These findings may inspire further chemical experimentation with tonewood processing for instrument making in the 21st century.
As a final chapter to this book, it is instructive to look at the general principles and practical considerations that have determined the materials from which musical instruments are made. There is a great deal of tradition, and a certain amount of mystique, about this subject, and some of the conclusions we draw may be hotly contested in the instrument-making community. This is all to the good, since it can lead to discussion, experimentation, and ultimately an advance in knowledge.
It is believed that acoustic quality and stability of wood are improved during long term ageing. However, it has recently been suggested that a part of those ageing effects are recovered by moistening at high humidity. Similar temporary effects have been recognized when wood is heated at high temperatures in the presence of moisture. Those temporary changes are speculated to be due to the physical ageing of amorphous wood polymers involving the temporary closure of micropores in the wood cell wall. For appropriate conservation of old wooden musical instruments and cultural properties, the recovery of physical properties due to moistening in humid condition should be taken into consideration. In addition, the temporary effect of heating should be eliminated for precise evaluation of the practical performances of heat-treated wood. This paper describes the reversible and irreversible changes in wood properties relevant to the practical quality of wooden crafts and musical instruments due to natural ageing and heat treatment.
Natural ageing of wood has a critical influence on ageing of musical instruments. Several possible factors can affect natural wood ageing. These include the combined effects of thermal oxidation by air oxygen, acid hydrolysis of bound water contained in cell walls, together with other acids contained in the wood. Ageing of structural parts of musical instruments is expressed by the modifications of the physical properties of wood owing to seasoning, long term static and dynamic loading. The relevant properties of wood are the density and the stiffnesses which characterise the orthotropic behaviour of this material. Damping characteristics are dependent on ageing of wood. Wood microstructure at different structural scales is modified by drying, creep phenomena induced by air humidity and temperature variations, long term static loading and vibration, chemical phenomena, micro-sorptive creep and reactions with different pollutants. Effects of continuous small amplitude vibrations of softwood and hardwood specimens on Young’s modulus along the fibres and internal friction was observed. On spruce resonance wood samples, submitted to several months of small amplitude forced vibrations, a small increase in the natural frequency was observed. Probably regular playing of violins and other string instruments improves their tonal quality through relatively small increases of wood stiffness and an important decrease in internal friction.
The effects of continuous vibration on the vibrational properties of wood were explained by the relaxation of drying stress.
La mesure de l'angle de perte est obtenue par le déphasage du signal au travers du montage dont la structure est analogue à une ligne à retard. La conception anirésonnante autorise une mesure sur la gamme audio via l'émission d'un chirp. De plus, la variation de l'angle de perte au cours du temps, pour une fréquence d'excitation maintenue, est identifiée.
ResearchGate has not been able to resolve any references for this publication.