Use of wood performed by heat-treatment for musical instruments

Alexander Pfriem, Prof. André Wagenführ,

Gunter Ziegenhals, Klaus Eichelberger

Faculty of Mechanical Engineering – Chair of Wood and Fibrous Materials Technology Institute for Research and Development of Musical Instruments – Adjacent Institute of TU Dresden

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 ofthe musical instrument industry could be the use ofthermally 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 dealerTheodor Nagel) in a „screening test“

• 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

retained modified

saw

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

density

velocitysoundc

ratioradiatioR

cR

ρ

ρ=

•No change of the anatomical structure of the modified wood butdefects 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 native maple, Transverse section

Figure 2: Scanning electron micrograph of thermally modified maple, Transverse section

Reduction of the elongation at rupture

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strain in %

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strong thermally modified spruce unmodified spruce sample

Reduction of damping

Comparison of the damping of modified and native twin samples in percent of the native twin sample

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spruce maple

Dimensional stability

Figure 1: Dimension change of nativemaple after artificial weathering

Figure 2: Dimension change of thermally modified maple after artificial weathering

The dimensional stability was analyzed by photogrammetric methods and CAD modelling:

Resorption of thermally modified spruce determined by DENT theory

Resorption isotherm curves by DENT Sorption model of mild modified spruce

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percent relative humidity H / %

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DENT Sorption modell (Resorption) M0_ads M1_ads M2_ads Measured Data Resorption

Mo

M2

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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

M

Comparison of the resorption isotherm curves

Comparison of the resorption isotherm curves of modified and native spruce by DENT Sorption model

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Resorption native spruce Resorption mild modified spruce Resorption strongly modified spruce

Conclusions for the use in musicalinstruments

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

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.

Three new application areas for thermally modified wood in smallmusical instruments:

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

Faculty of Mechanical Engineering – Chair of Wood and Fibrous Materials Technology Institute for Research and Development of Musical Instruments – Adjacent Institute of TU Dresden