The application of wood decay fungi to improve the acoustic properties of resonance wood for ...

255 Pages·2008·15.11 MB·English

The application of wood decay fungi to improve the acoustic
properties of resonance wood for violins

Thesis submitted in partial fulfilment of the requirements of
the degree Doctor rer. nat. of the
Faculty of Forest and Environmental Sciences,
Albert-Ludwigs-Universität
Freiburg im Breisgau, Germany

Melanie Spycher

Freiburg im Breisgau, Germany
2007
Dekan: Prof. Dr. Heinz Rennenberg
Referent: Prof. Dr. Francis W. M. R. Schwarze
Korreferent: Prof. Dr. Dr. h.c. Gero Becker
Datum der Disputation : 1. Februar 2008
CONTENT
TABLE OF CONTENT...........................................................................................................................i
ACKNOWLEDGMENTS.........................................................................................................................v
ABBREVIATIONS.................................................................................................................................vi
1. INTRODUCTION AND THEORETICAL BACKGROUND 1
1-1 VIOLIN AND VIOLIN MAKING: A BRIEF HISTORY..........................................................1
1-1.1 Violin: history and construction..............................................................................1
1-1.2 Physics of the violin...............................................................................................2
1-1.3 Stradivarius: mythos or reality?.............................................................................4
1-2 WOOD AND RESONANCE WOOD...................................................................................6
1-2.1 Wood structure.......................................................................................................6
1-2.2 Wood constituents.................................................................................................9
1-2.3 Wood for violin making..........................................................................................11
1-3 LITERATURE REVIEW ON ACOUSTICAL PARAMETERS..............................................14
1-3.1 Modulus of elasticity...............................................................................................16
1-3.2 Sound velocity........................................................................................................18
1-3.3 Radiation ratio........................................................................................................18
1-3.4 Damping factor and associated parameters..........................................................19
1-3.5 Parameters after orthotropic model.......................................................................20
1-3.6 Anisotropy factor....................................................................................................20
1-3.7 Acoustics invariants...............................................................................................21
1-4 WOOD DECAY...................................................................................................................22
1-4.1 Interactions between fungi and wood substrate....................................................22
1-4.2 Types of wood decay.............................................................................................24
1-4.3 Factors influencing the mode of decay..................................................................27
1-4.4 Wood decay fungi preserving stiffness..................................................................30
1-4.5 Wood decay fungi using in this study....................................................................30
1-5 HYPOTHESES AND OBJECTIVES...................................................................................33
1-5.1 State of the art.......................................................................................................33
1-5.2 Objectives and hypotheses....................................................................................34
1-5.3 Practical approach and construction of the thesis.................................................35
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2. MATERIALS AND METHODS 39
2-1 MEASUREMENTS OF PHYSICAL PROPERTIES............................................................39
2-1.1 Measurements of the resonance frequency of wood strips...................................39
2-1.2 Measurements and calculation of the modulus of elasticity..................................43
2-1.3 Strength and rupture tests.....................................................................................46
2-1.4 Measurements of the resonance frequencies with vibrometer..............................47
2-1.5 Ultrasound measurements.....................................................................................50
2-2 FUNGAL TREATMENTS....................................................................................................52
2-2.1 Sterilization methods (gas sterilization and steam sterilization)............................52
2-2.2 Treatment for wood strips......................................................................................52
2-2.3 Histological studies (Test after EN 113)................................................................60
2-2.4 Treatment of wood samples for ultrasound measurements..................................62
2-2.5 Treatment for small plates.....................................................................................63
2-2.6 Treatment for violin blocks.....................................................................................64
2-3 OTHERS INVESTIGATIONS.............................................................................................66
2-3.1 Light microscopy and Scanning Electron Microscopy...........................................66
2-3.2 Artificial ageing process.........................................................................................66
2-3.3 Evaluation of the laccase activity...........................................................................66
3. EVALUATION OF THE QUALITY OF RESONANCE WOOD 69
3-1 RELIABILITY OF THE STRIP MEASUREMENT SYSTEM................................................69
3-1.1 Geometry of the specimen and density.................................................................69
3-1.2 Set-up and repetitions of measurements...............................................................72
3-1.3 Moisture content and measured resonance frequency.........................................75
3-1.4 Comparison of static and dynamic modules of elasticity.......................................76
3-2 PHYSICAL AND HISTOLOGICAL ANALYSIS OF THE RESONANCE WOOD................79
3-2.1 Physical properties.................................................................................................80
3-2.2 Histological properties and structure of wood........................................................86
3-2.3 Analysis of a wood specimen from 1738...............................................................91
3-2.4 Analysis of an old fir specimen..............................................................................94
3-3 GLOBAL EVALUATION OF THE RESONANCE WOOD QUALITY..................................97
3-3.1 Acoustical parameters...........................................................................................97
3-3.2 Discussion of the Hypothesis n°1..........................................................................100
3-3.3 Anatomical considerations.....................................................................................101
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4. RESULTS: STRIPS MEASUREMENTS AND MICROSCOPIC INVESTIGATIONS 103
4-1 NORWAY SPRUCE WOOD...............................................................................................103
4-1.1 Norway spruce incubated with Climacocystis borealis and Phellinus hartigii.......103
4-1.2 Norway spruce incubated with Physisporinus vitreus............................................109
4-1.3 Norway spruce incubated with Phialocephala fortinii and Xylaria cubensis..........114
4-1.4 Norway spruce incubated with Deuteromycetes...................................................119
4-2 SYCAMORE WOOD...........................................................................................................130
4-2.1 Sycamore incubated with Schizophyllum commune.............................................130
4-2.2 Sycamore incubated with Xylaria longipes............................................................135
4-2.3 Sycamore incubated with Polyporus squamosus..................................................138
4-3 ADDITIONAL RESULTS....................................................................................................141
4-3.1 Control samples.....................................................................................................141
4-3.2 Histological studies................................................................................................143
4-3.3 Artificial ageing.......................................................................................................150
4-3.4 Evaluation of the laccase activity...........................................................................156
4-4 DISCUSSION.....................................................................................................................159
4-4.1 Norway spruce wood.............................................................................................159
4-4.2 Sycamore wood.....................................................................................................163
5. RESULTS: APPLICATION TO MUSIC INSTRUMENTS 167
5-1 ULTRASOUND MEASUREMENTS...................................................................................167
5-1.1 Results...................................................................................................................167
5-1.2 Comparison of resonance frequency and ultrasound measurements...................173
5-2 MEASUREMENTS ON SMALL WOOD PLATES..............................................................175
5-2.1 Results...................................................................................................................175
5-2.2 Comparison of vibrometer and resonance frequency measurements...................179
5-3 MEASUREMENTS ON VIOLIN WOOD BLOCKS..............................................................181
5-3.1 Results...................................................................................................................181
5-3.2 Comparison between strips specimens and violin blocks.....................................185
5-4 DISCUSSION.....................................................................................................................186
5-4.1 Comparison of measurements methods................................................................186
5-4.2 Incubation procedure.............................................................................................188
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6. DISCUSSION 189
6-1 DISCUSSION OF THE HYPOTHESES.............................................................................189
6-1.1 Alterations in acoustic properties (Hypothesis 2)..................................................189
6-1.2 Optimal stage of fungal degradation (Hypothesis 3).............................................195
6-1.3 Development of the parameters during incubation (Hypothesis 4).......................200
6-1.4 Application of the results to violin blocks (Hypothesis 5).......................................203
6-2 ADDITIONAL COMMENTS................................................................................................204
6-2.1 Modulus of rupture and density.............................................................................204
6-2.2 Fungal decay to substitute the climate..................................................................207
6-2.3 Remarks about aesthetics and sonority................................................................209
6-2.4 Resonance wood treated with wood decay fungi : An “adapted” material............211
7. CONCLUSIONS 213
7-1 CONCLUSIONS.................................................................................................................213
7-2 FURTHER RESEARCH AREAS........................................................................................214
7-3 SUMMARY.........................................................................................................................216
7-3.1 Summary................................................................................................................216
7-3.2 Zusammenfassung................................................................................................218
8. LITERATURE 221
9. ANNEXES 239
9-1 GENERAL ASPECTS ON WAVE MOTION.......................................................................239
9-1.1 Mathematical description.......................................................................................240
9-1.2 Sound waves in the air..........................................................................................241
9-1.3 Sound waves in solids...........................................................................................243
9-2 SOURCE AND ORIGIN OF FUNGI USED IN THE THESIS..............................................245
9-2.1 Origin of the fungal isolates...................................................................................245
9-2.2 Growth media.........................................................................................................246
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ACKNOWLEDGMENTS
First of all, I would like to thank Prof. Dr. Francis Schwarze for supervising me during my
PhD at the EMPA in St-Gallen. I appreciate the encouragements he provided me during these
three years. My special thanks also to Prof. Gero Becker for undertaking the co-supervision of
this thesis.
I am grateful to Prof. Siegfried Fink at the Forest Botany Institute in Freiburg in Breisgau for
his support during my stay in Freiburg and for co-supervising this work, as well as Ms.
Susanne Röske and Ms. Karin Waldmann to prepare the wood sections. I was also very
interesting in the opportunity to visit some lectures at the University: many thanks to Prof. S.
Fink, Prof. U. Seeling, Prof. G. Becker, and Prof. L. Jaeger to teach me basic knowledge
about the forestry.
I am particularly indebted to my colleagues from the EMPA, who made this work possible.
Many thanks to Klaus Richter, head of Wood Laboratory at EMPA, who provide my helpful
feed-back along my stay at the EMPA. I would like to mention Mr. Kurt Weiss and Mr.
Michael Strässle for carrying out the experiments with static methods; Mr. Daniel Heer for the
preparation of the wood specimens; Mr. Markus Heeb for conducting several pre-tests, and
finally Ms. Margrit Conradin to facilitate my administrative tasks. A special thanks go to
René Steiger for his support about the physical part of this research. I want also to thank my
collegues for their daily support: Ms. Bettina Lanz, Mr. Alex Skyba, Mr. Helge Landmesser,
Mr. Christoph Heuser and Mr. Mark Schubert.
The experiments with the vibrometer were carried out with the invaluable support of the
division of the Structural Engineering Research Laboratory at the EMPA in Dübendorf, in
particular Dr. Daniel Gsell and Sandy Schubert. My special thanks go to my PhD colleague
Arne Guelzow, who made the MATHLAB® program to evaluate the properties of the wood
specimens. My doctoral studies were possible thank to the financial support of the EMPA. I
want to acknowledge Prof. Louis Schlapbach and Dr. Peter Richner to believe in this project
and allow its funding.
I feel truly grateful to have had the opportunity to work with violinmakers and learn a little
from their craft. Mr. Michael Rhonheimer from Baden (CH) provided my invaluable
information about violins and all the violin blocks for my experiments. The other resonance
wood specimens were offer by Mr. Bernard Michaud from “Le Bois de Lutherie” in Fertans
(France). Finally, I want to thank Mr. Martin Schleske, from München (Germany) for his
fruitful collaboration.
Last but not least, I want to thank my family in Lausanne and in Bern to support my work
with love and comprehension during these three years, in particular my parents. My deepest
gratitude goes to my husband Adrian Spycher for, among other, his help for making the
program for strip measurements.
v
ABREVIATIONS
b Width of specimen
c Sound velocity
d Damping factor
EMPAxxx refers to the number of the strain at the Empa (see Table 77 and 78 for details)
EN European Norm
E Modulus of elasticity in the x-direction
x
f Resonance frequency
r
G Shear modulus in the plane xy
xy
H Emission factor
h Thickness of specimen
L Loudness factor
Longitudinal or axial direction
Length of specimen
MC Moisture content
MEA Malt extract agar
Mix refers to a fungal incubation with the five Deuteromycetes (C. globosum EMPA
569, H. grisea EMPA 571, P. setifera EMPA 572, P. mutabilis EMPA 573 and
T. spiralis EMPA 574).
MOE Modulus of elasticity (or Young’s modulus)
MOR Modulus of rupture (also called bending strength or strength at rupture)
R Radiation ratio
Radial direction
S , S , S refers to the secondary wall of the wood cell
1 2 3
STD Standard deviation
T Tangential direction
t Thickness of specimen
We Weeks
WL Weight loss
vi
1. Introduction and theoretical background
1-1 Violin and violin making: a brief history
1-1.1 Violin: history and construction
Throughout human history, music evolved together with the speech and the development of
the human being on one side, and with the creation of new music instruments on the other
side. At every stage of early human development, the spirit of new kinds of music instruments
can be detected. The origin of all string instruments were bows with one single string made of
animals’ catgut. Dating from the Neolithic age, reveal that pictures on the walls of caves show
the use of traditional bows to make sounds, accompanied by drums and dance. During this
age, different kinds of wood were used to make percussion and bow instruments, showing a
first discovery in the relation between the material and a “better” sound.
Before the Middle Ages, around the tenth century A.D., the “vielle” and the “rote” (Irish
version of the modern lyre) were invented. A fingerboard was added to the instrument,
allowing it to be bowed rather than simply plucked, as well as allowing the fingers to shorten
the strings to produce various tones. Even during early days, the instrument was played on the
left shoulder or breast, which was unusual, because most string instruments were still held on
the knees for a few more centuries. The twelfth century brought the final evolution of the
vielle. It was, at that time, similar to a modern guitar in cut. It was a widely used instrument
during this period due to its ease of handling, its wide tonal range, and the ease of playing the
scales. For this reason, the instrument was used with up to four strings instead of only one or
two. Until the 16th century, some instruments even had five strings.
Three other instruments appeared before 1500, one of which, the “viola da gamba” (held on or
between the knees) is sometimes still played today. Another was a bowed instrument called
the “lire da braccio”. The third is called the “viola da braccio” originally with three or four
strings, which is the direct predecessor of the violin. Since the fifteenth century, it became a
four-stringed instrument and adopted other modern characteristics, such as the peg box and
tuning in fifths. This method of tuning allows the musician to use four fingers, which is ideal
for short-arm instruments. The shape of the sound holes also changed from crescents to the f-
shape used today, and became known as “f-holes” (Fletcher and Rossling, 1998).
The violin we know today appeared between 1500 and 1550. Its actual shape (Figure 1) was
first mastered by Italian violinmakers and has not changed since the last 400 years. The
natural evolution, which led to the creation of the violin, reached its maximum with Stradivari
and Guarneri at the end of the seventeenth century. Even today, their violins are considered
among the best of the world. This evolution was also very strongly related to the demand of
the composers each new difficulty in a music piece leading to an adaptation of the instrument,
permitting the musician to reach the virtuosity requested from the composer.
1
C.

A. B.

Figure 1: Illustration of the shape of the different precursors of a modern violin (Michels,
1990) / (A) Vielle (B) Lire da braccio (C) Viola da gamba
1-1.2 Physics of the violin
The actual construction of the violin is represented in Figure 2. The scroll, bridge, back plate
and ribs are made of curly maple, which has a great aesthetic importance. The top, sound post
and corners blocks are all made of Norway spruce (Veitl, 1987), which is used for all
vibrating pieces. All parts are manufactured by hand, especially the top and back plates,
whose curvatures are adapted to the natural structure of wood (Johnson and Courtnall, 1999).
To create a sound, one of the strings has to be put into vibration, either with a bow or by
plucking with fingers (Gough, 2000). This vibration is transmitted to the top plate through the
bridge and through the sound-post to the back-plate (for mathematical description, cf. Cremer,
1981). The effect of this vibration on the violin body and the emitted loudness level varies
strongly with the frequency of vibration (Figure 3). This loudness curve is specific for each
violin and the way it has been played during recording. First, the Helmholtz resonance (also
called “air resonance”) appears at a very low frequency - 275 Hz (Dünnwald, 1990) or 286 Hz
(Schleske, 1990)-, which is the phenomenon of air resonance in a cavity (Schelleng, 1963).
The second peak, which is called “main body resonance”, is evident when the top and back
plates are vibrating simultaneously. The top and back plates are normally tuned so that their
difference would be 3 semitones, leading to a broad resonance peak (Huchtins, 1981b). These
two ways of resonance are mainly influenced by manufacturing and the curvatures of the
plates and are responsible for the ground sonority of the violin (Dünnwald, 1990). The best
violins are characterized by the Helmholtz resonance and the body resonance strongly
correlated with the frequency of the two open middle strings (Hutchins, 1962).
2