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Submitted on 19 Dec 2018
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Clarifying the concept of “resonance wood”: luthiers’ empirical expertise versus assessment of wood
structural/visual and vibrational properties
Capucine Carlier, Iris Brémaud, Joseph Gril
To cite this version:
Clarifying the concept of “resonance wood”: luthiers’ empirical expertise
versus assessment of wood structural/visual and vibrational properties
CARLIER Capucine
1, BREMAUD Iris
1, GRIL Joseph
11
Wood Team, Laboratory of Mechanics and Civil Engineering (LMGC), CNRS, Université Montpellier 2, France
1. Introduction
2. Objective
3. Materials and methods
8. Conclusion and perspectives
The objective of this study is to improve the understanding of the interactions between physic-mechanical properties of resonance wood, their natural variability, and the actual expertise of violin makers in the selection and qualification of their raw material.
Measurement of visual/structural characteristics (growth-ring uniformity and percentage of latewood).
o Spruce (Picea abies [L.] Karst)
o Viola and violin soundboard, Quality grades “Excellent” and “Master grade” o 70 samples in radial direction (120×2,5×12mm, R×T×L) and 116
samples in longitudinal direction (12×2,5×150mm, R×T×L).
→
Characterization of tonewood :
o face to face interview
o First step: Luthiers of Montpellier
o Organized by module (Maker’s Profile, Concept of
quality, Wood supply, Wood Criteria Choices for top plates, for back & sides, for bows, Treatments and varnish Relation to scientific and historical research, Questions and remarks)
o Survey suitable to be adapted to different kind of
instrumental making
→
Development of a survey to identify violin
makers’
opinions
and
practices
on
both
qualitative and quantitative grounds
4. Concept of instrument quality
7. Relation to sciences
6. Properties
• Characterization of the physical and vibrational properties and
acoustical indexes of the specimens
To clarify this concept of quality, the makers defined a good instrument by using :
- Physical criteria, "powerful", “with timbre" and "easy to play"
- a notion of pleasure “sensation of
evidence“, "instrument that is unanimously" "that pleases the one who plays"
5. Supply and wood choice
Ring width reflects the vibrational properties, while latewood provides informations on the acoustical indexes.
Visual parameters = Good perception of wood mechanical phenomena
0% 50% 100%
Grade Test par des outils Test mécanique "à la main" Evaluation acoustique "à la main" Evaluation personnelle visuelle Evaluation personnelle de la densité
Très important Important
Peu important Insignifiant Non concerné
Our correlations between visible structural characteristics, density and vibrational properties in spruce “resonance wood” are not typical of classical softwoods
Why Violin makers trust their suppliers but pay little attention to grades posted?
⇒ Acquisition and
image processing
techniques in
improvement
⇒ Necessity to integrate the
suppliers in the survey
High variability intra and inter board suggesting that a single specimen may not be representative of the properties of the entire board. 0 20 40 60 80 100 Qualité sonore Qualité globale 0% 50% 100% Couleur Test de flexion Facilité de travail Stabilité Toucher Dureté Test acoustique Temps de séchage Largeur de cerne Homogénité des cernes % Bois final/initial Poids/densité Débit Très important Important Peu important Insignifiant Ne sais pas
Importance scale of different fabrication parameters in sound quality and quality of instrument
Vybris device, a non contact forced vibrations of free-free beams developed in LMGC
Importance scale of different criteria to qualify the spruce wood Importance scale of different kinds of evaluations when buying resonance wood
Relation between visual characteristics of spruce wood and its properties
0 0.5 1 1.5 2 2.5 3 3.5 0 2 4 6 8 10 12
Radial distance (cm) from the center to the sapwood
R in g w id th (m m )
5 different Violin soundboards
Visual characteristics analyzed by image J
20 24 28 32 36 12 9 6 3 0
Radial distance (cm) from the center to the sapwood
S p e ci fi c M o d u lu s E ’ L /ρ (G P a )
All makers buy their wood from a specialized supplier, whom they trust and never choose directly in the forest. To choose their tonewoods, they mainly assess density and visual
criteria.
Interest scale of violin makers for different research areas
=> Necessity to construct a
model to evaluate the properties
of a full violin plate from
sampling fabrication offcuts
Wood as material of many musical instruments plays an essential role in their acoustic, aesthetic or technical quality, therefore in their identity. Among the many wood used in musical instruments, the term "resonance wood" is often used to describe those used for the soundboard of string instruments (spruce) and for the resonator box ( “fiddleback” maple).
This study shows the peculiarity of
spruce “resonance wood” in regards to
classical softwoods . Empirical choice by violin makers, based on perceptual
criteria that can be visual,
physic-mechanical, auditory, are relevant to
the acoustic properties measured but
will require a more detailed study to evaluate the respective contribution of these different fields of perception.
Evolution of the ring width and the specific modulus of violins soundboards according to the radial distance R Rw (mm) Lw (%) Density ρ Density ρ -0,53 0,99 EL/ρ -0,8 0,69 0,63 ER/ρ 0,69 -0,16 -0,07 tanδL 0,72 -0,4 -0,31 tanδR -0,85 0,4 0,33 zL -0,62 0,99 0,99 RL 0,31 -0,92 -0,95 ACEL -0,01 -0,68 -0,74
⇒ Is the confidence of the makers in the suppliers coming from
the peculiarity of this pre-selected material?
Sampling plan 0% 50% 100% Dendrochronologie Acoustique physique Conservation Psycho-acoustique Traitement, Vieillissement Vernis Histoire des arts et des techniques Foresterie, Sciences du bois Tracé, dessin Mécanique et déformation Très intéressé Intéressé Moyennement intéressé Peu intéressé Pas intéressé
• To broaden our survey to a national and international scale • To collect sampling fabrication offcuts from violin makers
• To construct a model to evaluate the properties of a full violin plate • To enlarge the study to ‘fiddleback’ maple
• To study microstructural characteristics of resonance woods
⇒Perspectives D e n si ty ρ [g /c m 3 ] S p e ci fi c M o d u lu s E / ρ [G P a ] Ring width [mm] Resonance wood Classical spruce measured by Kubojima and al., 1997
The “resonance woods” for the making of violin family have benefited from more research than other instrument making woods, but the interactions between different disciplines and viewpoints in this field has seldom been addressed.
Correlations between properties, acoustical index and visual characteristics of wood
Acoustical properties of resonance wood
Psycho-sensory evaluation of wood choice by craftsmen
Survey with violin makers and foresters
General approach Resonance wood choice appears for
craftsmen to be a determining factor in sound quality of the instrument.
Ring width [mm]
5 different Violin soundboards
Cutting plan & direction Density Percentage of latewood Growth ring uniformity Growth ring width Drying time Acoustical test Stiffness Touch Stability Work ability Bending test Color
Main criteria to qualify the spruce wood are: cutting, density, percentage of latewood, growth ring uniformity and width.
What is the relationship between these visual criteria and the mechanical and acoustical properties of wood?
Very important Important
Slightly important Not at all important Don’t know
Personal evaluation of density Visual personal evaluation Acoustical evaluation “by hand” Mechanical evaluation “by hand” Tools assessment Quality grades from suppliers
Considerable interested
Interested
Some interested
Little interested
Not at all interested Very important
Important
Slightly important Not at all important Not concerned
o Makers rely mainly on
empirical approaches,
and also historical for their practices , but report a lot of interest in the scientific approach of resonance wood.
o Their interests are mostly
related to the history of art and techniques, to the drawing, varnishes and to the mechanics and wood science.
Mechanics and deformation Drawing, design Forestry, Wood sciences History of arts and techniques Varnish Treatments, ageing Psychoacoustics Conservation Physical acoustics Dendrochronology Back plate wood Top plate wood
Other wood parts Design Pre stresses Finishing touch Adjustment Varnish Sound quality
