PlosONE publishes secret of Stradivari violins in wood density

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Research Article

Formal Correction: This article has been formally corrected to address the following errors.

A Comparison of Wood Density between Classical Cremonese and Modern Violins

Berend C. Stoel1*, Terry M. Borman2

1 Department of Radiology, Division of Image Processing, Leiden University Medical Center, Leiden, The Netherlands2 Borman Violins, Fayetteville, Arkansas, United States of America


Abstract

Classical
violins created by Cremonese masters, such as Antonio Stradivari and
Giuseppe Guarneri Del Gesu, have become the benchmark to which the
sound of all violins are compared in terms of their abilities of
expressiveness and projection. By general consensus, no luthier since
that time has been able to replicate the sound quality of these
classical instruments. The vibration and sound radiation
characteristics of a violin are determined by an instrument's geometry
and the material properties of the wood. New test methods allow the
non-destructive examination of one of the key material properties, the
wood density, at the growth ring level of detail. The densities of five
classical and eight modern violins were compared, using computed
tomography and specially developed image-processing software. No
significant differences were found between the median densities of the
modern and the antique violins, however the density difference between
wood grains of early and late growth was significantly smaller in the
classical Cremonese violins compared with modern violins, in both the
top (Spruce) and back (Maple) plates (p = 0.028 and 0.008,
respectively). The mean density differential (SE) of the top plates of
the modern and classical violins was 274 (26.6) and 183 (11.7)
gram/liter. For the back plates, the values were 128 (2.6) and 115
(2.0) gram/liter. These differences in density differentials may
reflect similar changes in stiffness distributions, which could
directly impact vibrational efficacy or indirectly modify sound
radiation via altered damping characteristics. Either of these
mechanisms may help explain the acoustical differences between the
classical and modern violins.

Citation: Stoel BC, Borman TM (2008) A Comparison of Wood Density between Classical Cremonese and Modern Violins. PLoS ONE 3(7):
e2554.
doi:10.1371/journal.pone.0002554

Editor: Ananth Grama, Purdue University, United States of America

Received: March 18, 2008; Accepted: May 30, 2008; Published: July 2, 2008

Copyright:
© 2008 Stoel, Borman. This is an open-access article distributed under
the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium,
provided the original author and source are credited.

Funding: The authors have no support or funding to report.

Competing interests: The authors have declared that no competing interests exist.

* E-mail: B.C.Stoel@lumc.nl


Introduction

For
the past 300 years, the violins of Antonio Stradivari (1634–1737) and
Giuseppe Guarneri del Gesu (1698–1744) have excelled in molding a
many-nuanced sound that seems to better express the intent of composers
and musicians. These classical Cremonese violins have become the
benchmark to which all violins are compared. Presently, many believe
that violin craftsmanship is at its most advanced point since the days
of the Cremonese luthiers, and yet instruments produced today do not
match the classical instruments in their abilities of expressiveness
and projection. It remains unclear what has kept them, for such a long
time and through such changing musical needs, as the most sought after.

Research into the
production of high quality sound has focused on a wide range of
variables, such as the arching design and contours [1], plate thickness [2], the impact of varnish layers [3], [4],
as well as the various elements of set-up, such as the angle of the
neck, the impact of the fingerboard and the angle of the strings
passing over the bridge. Extensive work has been done searching for the
ideal wood properties [5][9],
although none corresponding exactly to known Cremonese wood properties
as most tested samples have been of significantly higher median density
than those found to be the case in this study.

Tracheid clusters,
produced during annual growth cycles of the tree, create the prominent
light/dark grain lines in wood. Early growth wood, created during
spring, is primarily responsible for water transport and thus is more
porous and less dense than late growth wood, which plays more of a
structural support role [10],
of much more closely packed tracheids. Wood is an orthotropic material,
having differing mechanical properties in three directions: along the
grain, across the grain, and slabwise (circumferentially) [11].
The differences in density between early and late growth wood may
impact the detailed vibrational behavior, either directly or through
altered stiffness or damping characteristics due to these variations.
The complex three-dimensional shape of the violin body means that
vibration within the audio range involves extensional, bending and
shear deformations of the wooden plates involving all three directions.
Researchers have commented on wood selection preferences based on these
differentials [9],
although detailed data are lacking on fine instruments. Wood density is
difficult and invasive to measure directly, as an isolated part of the
instrument, wrapped in a waterproof container, must be immersed in
water to estimate its volume, and the density is calculated by dividing
its weight by this volume [12].
Furthermore, this technique does not provide data on density
differentials. Computed Tomography (CT) has been used by other
researchers [13][15] primarily for visual analysis, without fully employing its ability to quantify density or density differentials.

Here we examine the
wood density of five classical Cremonese violins; three by Giuseppe
Guarneri del Gesu and two by Antonio Stradivari, using quantitative CT
densitometry, a rapid and non-invasive technique usually applied in a
medical setting [16].
The results from these classical violins were compared to those of
eight contemporary violins, made by T. Borman, A.T. King and G. Rabut (Table 1),
in order to determine whether objective measurements of material
properties can explain the historical consensus on the differences in
quality of sound between classical Cremonese and modern violins. At the
end of this article we will outline in detail our methodology.

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Table 1. Table of instruments studied.

doi:10.1371/journal.pone.0002554.t001