University of Dresden study of musical

Faculty of Mechanical Engineering – Chair of Wood and Fibrous Materials Technology
Institute for Research and Development of Musical Instruments – Adjacent Institute of TU Dresden
Use of wood performed by heattreatment for musical instruments
Alexander Pfriem, Prof. André Wagenführ,
Gunter Ziegenhals, Klaus Eichelberger
Göttingen, 07.10.2005
Introduction – The problem
• Increasing demand in high quality musical instruments on the
world market
• Strong competition in the cheap segment of musical instruments
• Clear reduction of specific wood for musical instruments in the
next years
– on the national market
– and international market
• Use of tropical wood for musical instruments
Preparing investigations to support the manufactures of musical
instruments are necessary
Goals of a modification
Working hypothesis of the project:
„One of the possibilities to supply the timber demand of
the musical instrument industry could be the use of
thermally modified wood“
The following goals are to be carried out by the modification:
• Use of woods, which were so far not used for musical
instruments
• Replacement for expensive or rare import timbers
• Improvement of the characteristics of wood for the use in
musical instruments
• Improvement of the sorption behaviour: Decrease shrinking
behaviour
• Artificial aging of the wood
• Decrease of long storage times
Analysis of characteristics
• Wood of 4 European manufactures
(Thermoholz Austria, Stellac Oy, Plato,
modified wood of the tone wood dealer
Theodor Nagel) in a „screening test“
retained
• Testing of wood twin-samples
one twin is retained, one is modified
of Thermoholz Austria and Theodor
Nagel
• Use of 4 kinds of wood: spruce, fir,
beech, maple
• Test of 3 different modification levels
(180-220°C)
• Analysis of anatomical, mechanical,
chemical and acoustic properties
• Experiments to the dimensional stability,
moisture absorption and moisture
transport
board
saw
modified
Some results of the screening test
• Mild treatment leads to increase of Young‘s modulus, sound
velocity and decrease damping
• Strongly modified wood may not reach the proportional limit by
bending testing, a strong modification leads to not acceptable
losses of strength
• The radiatio ratio (soundvelocity over density) increase by mild
treatment
c
R=
ρ
R radiatio ratio
c sound velocity
ρ density
• No change of the anatomical structure of the modified wood but
defects and microcracks were analysed
• High dimensional stability of thermally modified maple
• Reduced water-sorption of thermally modified wood (determined
by DENT theory)
Defects and microcracks
Figure 1 : Scanning electron micrograph of Figure 2: Scanning electron micrograph of
thermally modified maple, Transverse
native maple, Transverse section
section
Reduction of the elongation at
rupture
80
strong thermally modified spruce
unmodified spruce sample
70
bending stress in MPa
60
50
40
30
20
10
0
0
0,2
0,4
0,6
strain in %
0,8
1
1,2
Reduction of damping
Comparison of the damping of modified and native twin samples in percent of the native twin sample
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
weak modification
middle modification
spruce
strong modification
weak modification
strong modification
maple
Dimensional stability
The dimensional stability was analyzed by
photogrammetric methods and CAD modelling:
Figure 1: Dimension change of native
maple after artificial weathering
Figure 2: Dimension change of thermally
modified maple after artificial weathering
Resorption of thermally modified
spruce determined by DENT theory
Resorption isotherm curves by DENT Sorption model of mild modified spruce
DENT Sorption modell (Resorption)
M0_ads
M1_ads
M2_ads
Measured Data Resorption
25
M0 = moisture content of complete monolayer coverage of all available sorption sites
M1 = moisture content of primary water
M2 = moisture content of secundary water
M = complete moisture content M = H / (A+B*h-C*h^2) = M1 + M2
percent moisture content M / %
20
15
M
10
M2
Mo
5
M1
0
0
10
20
30
40
50
60
percent relative humidity H / %
70
80
90
100
Comparison of the resorption
isotherm curves
Comparison of the resorption isotherm curves of modified and native spruce by DENT Sorption model
35
Resorption native spruce
Resorption mild modified spruce
Resorption strongly modified spruce
percent moisture content M / %
30
25
20
15
10
5
0
0
10
20
30
40
50
60
percent relative humidity H / %
70
80
90
100
Conclusions for the use in musical
instruments
Advantages of thermally modified wood:
• Increase of the Young’s modulus
• Reduced moisture sorption
• Larger dimensional stability
• Better durability
• Better acoustic characteristics like damping, sound velocity and
Radiatio ratio (soundvelocity over density)
Disadvantages of thermally modified wood:
• Reduction of the elongation at rupture
• Reduced strength
• Embrittlement of the material
• Defects and microcracks in anatomical structure
Production and Testing of musical
instruments
Figure 1: Guitar made of thermally
modified spruce (right) and unmodified
spruce (left)
Figure 2: Mouth organs with body
(comb) made by thermally modified
maple
Testing of the guitars
Frequency characteristics of three guitars made with sound boards of thermally
modified wood (F03303 to 05) compared with an identically constructed reference
instrument
Conclusions of the project
Three new application areas for thermally modified wood in small
musical instruments:
1. Use in musical instruments, high dimensional stability and a
small moisture sorption are required, for example in wind
instruments, in addition, stringed and fretted instruments,
which are played in different extreme climatic zones of the
earth.
2. Use
in
musical
instruments,
where
specific
sound
characteristics are required, otherwise only be reached by use
of woods stored for a very long time, for example for stringed
and fretted instruments. A reduction of storage times and that
way a significant saving on storage costs can be obtained.
3. Since the thermally improved wood shows similar sound
characteristics as naturally aged wood, it is suited for the
restoration and reconstruction of old musical instruments.
Faculty of Mechanical Engineering – Chair of Wood and Fibrous Materials Technology
Institute for Research and Development of Musical Instruments – Adjacent Institute of TU Dresden
Thank you for your attention!
Alexander Pfriem, Prof. André Wagenführ, Gunter
Ziegenhals, Klaus Eichelberger - Use of wood performed
by heat-treatment for musical instruments – Göttingen,
07.10.2005