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Thermally Modified Wood for Use in Musical Instruments

September 2015
Drvna industrija 66(3):251-253

DOI:10.5552/drind.2015.1426

Authors:

Eberswalde University for Sustainable Development

The unique mechanical and acoustical properties of wood and its aesthetic appeal still make it the material of choice for musical instruments. Here tropical hardwoods are typically used in musical instruments. This paper gives an overview of how the use of thermally modified wood can contribute to the use of raw materials for musical instruments. It is shown that a mild thermal treatment leads to clear changes of the measurable acoustic characteristics, such as Young’s modulus, damping and sound velocity. In conclusion, thermally modified wood (mild treatment) is a material with favorable characteristics for making musical instruments.

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......................Pfriem: Thermally Modiﬁ ed Wood for Use in Musical Instruments

DRVNA INDUSTRIJA 66 (3) 251-253 (2015) 251

Alexander Pfriem

Thermally Modified

Wood for Use in Musical

Instruments

Toplinski modificirano drvo za izradu

glazbenih instrumenata

Review paper • Pregledni rad

Received – prispjelo: 21. 8. 2014.

Accepted – prihvaćeno: 20. 5. 2015.

UDK: 630*835.2; 630*842

doi:10.5552/drind.2015.1426

ABSTRACT • The unique mechanical and acoustical properties of wood and its aesthetic appeal still make it the

material of choice for musical instruments. Here tropical hardwoods are typically used in musical instruments.

This paper gives an overview of how the use of thermally modiﬁ ed wood can contribute to the use of raw materi-

als for musical instruments. It is shown that a mild thermal treatment leads to clear changes of the measurable

acoustic characteristics, such as Young’s modulus, damping and sound velocity. In conclusion, thermally modiﬁ ed

wood (mild treatment) is a material with favorable characteristics for making musical instruments.

Key words: acoustical wood properties, musical instruments, thermally modiﬁ ed wood

SAŽETAK • Zbog jedinstvenih mehaničkih i akustičnih svojstava te estetskih obilježja drvo se često rabi kao

materijal za izradu glazbenih instrumenata. U radu se opisuje kako uporaba toplinski modiﬁ ciranog drva može

pridonijeti boljoj raspoloživosti sirovine za izradu glazbenih instrumenata. Pokazalo se da blaga toplinska obrada

drva dovodi do jasnih promjena mjerljivih akustičnih veličina kao što su Yangov modul elastičnosti, prigušenje i

brzina zvuka. Zaključno, drvo koje je umjereno toplinski modiﬁ cirano ima poželjna obilježja za izradu glazbenih

instrumenata.

Ključne riječi: akustična svojstva drva, glazbeni instrumenti, toplinski modiﬁ crano drvo

Author is professor at Eberswalde University for Sustainable Development - University of Applied Sciences, Eberswalde, Germany.

Autor je profesor Sveučilišta održivog razvoja u Eberswaldu – Sveučilište primijenjenih znanosti, Eberswalde, Germany.

1 INTRODUCTION

1. UVOD

The unique mechanical and acoustical properties

of wood and its aesthetic appeal still make it the mate-

rial of choice for musical instruments. Worldwide, sev-

eral hundred wood species are available for making

wind, string, or percussion instruments (Wegst, 2006).

Here tropical hardwoods are typically used in musical

instruments. Examples for tropical hardwoods in musi-

cal instruments are:

• Ebony (e.g. fretboards)

• Brazilian rosewood (e.g. bottom and ribs of guitars)

• Mahogany (e.g. in guitars and violins)

• Páu brasil (Pernambuco) (bows of stringed instru-

ments)

• Grenadilla (e.g. ﬂ ute and clarinets)

These wood species are often illegally cut down.

Some species (e.g. Brazilian Rosewood, some Mahog-

any species, Pernambuco) are protected by CITES

(Convention on International Trade in Endangered

Species). Today, the demand increases to replace tropi-

cal wood in musical instruments. The search for alter-

native wood has to take into consideration anatomical

features, physical, mechanical, acoustical, and chemi-

cal properties.

On the other hand, the desire of musical instru-

ment manufactures to reduce negative characteristics

Pfriem: Thermally Modiﬁ ed Wood for Use in Musical Instruments ......................

252 DRVNA INDUSTRIJA 66 (3) 251-253 (2015)

of the raw material wood by special modiﬁ cation pro-

cesses has existed for a century now. An overview of

different historical modiﬁ cation processes can be found

in the paper by Martius (1999). Many of these process-

es were not further pursued. Today, however, the ques-

tion arises whether some of these historical procedures,

with consideration of new, further developed methods,

can help to satisfy the increasing demand of high-qual-

ity wood for musical instruments.

This paper gives an overview of how the use of

thermally modiﬁ ed wood can contribute to the use of

raw material for musical instruments.

2 OVERVIEW

2. PREGLED LITERATURE

In some scientiﬁ c papers, the effect of heat treat-

ment upon the acoustic properties of wood are de-

scribed. Gadd and D’Arcy (1986) state that the heat

treatment of spruce gives no statistically signiﬁ cant ef-

fect on characteristic values of wood. Such treatments,

with temperatures between 110 °C and 115 °C, result

only in slight changes in material properties.

A study with several producers of guitars from

Finland, conducted between 1998 and 2002, shows the

use of thermally modiﬁ ed wood, made by the ﬁ nish

VTT process, in musical instruments. It was clearly ob-

served that the treatment temperature affects the

achieved sound velocity of wood samples. The conclu-

sion of this research is that when tonewoods are ther-

mally treated in a speciﬁ c manner, the changes in wood

are the same as in naturally aged wood, whereas certain

qualities of wood improve while the wood maintains

its workability and strength. Further, the beneﬁ ts of

thermal-treatment seem more apparent when wood

species of higher quality are treated (results published

in Thompson, 2006).

Obataya et al. (2003, 2006a, 2006b) showed the

inﬂ uence of high temperature kiln drying on the practi-

cal performances of Japanese cedar wood. This heat

treatment is sometimes regarded as an accelerated age-

ing. However, heat-treated wood and aged wood are

qualitatively different with respect to their hygrosco-

picity and vibrational properties.

The aim of the work of Pfriem et al. (2005) and

Wagenführ et al. (2006) was to compare thermally

modiﬁ ed and unmodiﬁ ed twin samples of resonance

spruce wood for sound boards. By a speciﬁ c thermal

treatment, physical-technical characteristics of wood

can be changed in such a way that they correspond bet-

ter to the requirements of wood used for sound boards

than unmodiﬁ ed woods. More serious is the reduced

moisture sorption, larger dimensional stability, better

durability as well as acoustic characteristics. The ef-

fects of the relatively mild thermal treatment (180 °C)

can be compared with an “artiﬁ cial aging”. Due to the

thermal modiﬁ cation, objectively measurable parame-

ters are improved, and hence it can be concluded that

sound characteristics are improved, too.

Pfriem (2006) and Pfriem et al. (2007) built and

tested musical instruments made with thermally modi-

ﬁ ed wood. For the purpose of this study, guitars, vio-

lins, and harmonicas (partly) made from thermally

modiﬁ ed wood were prepared and tested. The analysis

of possible application areas in musical instruments

was not only in the foreground of this investigation.

Rather, the physical changes of material behavior

caused by thermal modiﬁ cation were investigated with

special reference to the general requirements for mak-

ing instruments.

Mohebby et al. (2007) investigated the inﬂ uence

of hydrothermal modiﬁ cation on musical properties of

mulberry wood. This wood is used traditionally for

making instruments in Iran. Due to the improved hy-

drophobicity and dimensional stability, sound proper-

ties became better by hydrothermal modiﬁ cation.

Investigations focused on the use of thermally

modiﬁ ed wood for statically and dynamically highly

stressed components of musical instruments were car-

ried out by Zauer and Pfriem (2010). The cross sec-

tions of thermally modiﬁ ed maple (Acer pseudoplata-

nus L.) were reinforced with carbon ﬁ

bers reinforced

epoxy resin in a single-stage process. The results clear-

ly show that thermal treatment improves the sound

quality of wood. Additionally, the reinforcement with

carbon ﬁ ber increases the static and dynamical proper-

ties of thermally modiﬁ ed wood.

Zauer et al. (2014) modiﬁ ed European beech

(Fagus sylvatica L.) to increase the acoustic and me-

chanical properties similar to Hard maple (Acer sac-

charum) to substitute the latter especially in highly

stressed components of musical instruments. A rela-

tively mild treatment, at temperatures ranging between

140 °C and 160 °C and a treatment time of 12 h, leads

to an improvement of both mechanical and acoustical

properties of beech wood. E.g. the average damping

values of beech wood were improved to the level of

hard maple wood by this mild treatment procedure.

The materials may be used as substitution material in

electric guitars.

3 CONCLUSIONS

3. ZAKLJUČAK

Apart from a change of the acoustically relevant

characteristics, thermally modiﬁ ed wood exhibits ad-

vantages concerning the dimensional stability and

sorption in regard to changing climatic conditions. On

the other hand, the modiﬁ cation of wood at high tem-

peratures results in a reduction in strength and tough-

ness. Certainly, a mild thermal treatment (modifying at

160-180 °C in oxygen-poor atmosphere) leads to clear

changes of the measurable acoustic characteristics,

such as Young’s modulus, damping and sound velocity.

In conclusion, thermally modiﬁ ed wood (mild treat-

ment) is a material with favorable characteristics for

making musical instruments. A pre-selection of raw

materials is, however, absolutely necessary. Inappro-

priate materials can hardly be improved by thermal

modiﬁ cation. Due to these investigations, traditional

production technologies for making musical instru-

ments can be adapted to use thermally modiﬁ ed wood

......................Pfriem: Thermally Modiﬁ ed Wood for Use in Musical Instruments

DRVNA INDUSTRIJA 66 (3) 251-253 (2015) 253

in musical instruments. For thermally modiﬁ ed wood

(mild treatment), three application areas are possible:

• Use in instruments, where high dimensional stabil-

ity and low moisture sorption and reduced reaction

to climatic variability are required.

• Use in musical instruments, where speciﬁ c sound

characteristics are required, which otherwise can

only be attained by use of wood stored for a very

long time. A reduction of storage time and in that

way a signiﬁ cant saving on storage costs can be ob-

tained. Thermally modiﬁ ed wood will not replace

wood used so far, but it can be a successful supple-

ment. Through the use of thermally modiﬁ ed wood,

the assortment of musical instrument manufactur-

ers can be widened or extended.

• Since the thermally improved wood shows similar

sound characteristics to naturally aged wood, it is

suited for the restoration and reconstruction of old

musical instruments.

In addition, based on the results obtained, it can

be concluded that thermally modiﬁ ed timber can also

be used for other applications. As musical instruments

represent the “upper class” in the wood processing in-

dustry, such statements regarding the workability and

usability can also be applied to other areas.

4 REFERENCES

4. LITERATURA

1. Gadd, C.; D’Arcy, J., 1986: On the effect of heat treat-

ment upon acoustic properties of spruce. Journal of the

Violin Society of America, 7 (4): 157-166.

2. Martius, K., 1999: Herkunft, Lagerung und Präparation

von Tonhölzern im Spiegel historischer Quellen. Scripta

Artium 1: 23-34.

3. Mohebby, B.; Yaghoubi, K.; Roohnia, M., 2007: Acous-

tic Properties of Hydrothermally Modiﬁ ed Mulberry

(Morus alba L.) Wood. Proceedings of the third Europe-

an Conference on Wood Modiﬁ cation, Cardiff, 283-286.

4. Obataya, E.; Higashihara, T.; Gril, J., 2003: Effects of

heat treatment on the hygroscopicity of wood. Proceed-

ing of the Second International Conference of the Euro-

pean Society for Wood Mechanics, Stockholm, 33-37.

5. Obataya, E.; Shibutani, S.; Hanata, K.; Doi, S., 2006a:

Effects of high temperature kiln drying on the practical

performances of Japanese cedar wood (Cryptomeria ja-

ponica D. Don) I: changes in hygroscopicity due to heat-

ing. Journal of Wood Science, 52(1): 33-38.

http://dx.doi.org/10.1007/s10086-005-0716-9

6. Obataya, E.; Shibutani, S.; Hanata, K.; Doi, S., 2006b:

Effects of high temperature kiln drying on the practical

performances of Japanese cedar wood (Cryptomeria ja-

ponica D. Don) II: changes in mechanical properties due

to heating. Journal of Wood Science, 52(2): 111-114.

http://dx.doi.org/10.1007/s10086-005-0748-1

7. Pfriem, A.; Wagenführ, A.; Ziegenhals, G.; Eichelberger,

K., 2005: Use of wood performed by heat-treatment for

musical instruments. Proceedings of the Second European

Conference on Wood Modiﬁ cation, Göttingen, 390-397.

8. Pfriem, A., 2006: Untersuchungen zum Materialverhalten

thermisch modiﬁ zierter Hölzer für deren Verwendung im

Musikinstrumentenbau. Ph.D. thesis TU Dresden.

9. Wagenführ, A.; Pfriem, A.; Grothe, T.; Eichelberger, K.,

2006: Untersuchungen zur vergleichenden Charakter-

isierung von thermisch modiﬁ zierter Fichte für Resonan-

zdecken von Gitarren. Holz als Roh- und Werkstoff, 64:

313-316. http://dx.doi.org/10.1007/s00107-005-0057-9

10. Pfriem, A.; Eichelberger, K.; Wagenführ, A., 2007:

Acoustic properties of thermally modiﬁ ed spruce for use

for violins. Journal of the Violin Society of America:

VSA-Paper 21(1): 102-111.

11. Thomson, H. S., 2006: Thermo-treated Wood... Vintage

Tone or Voodoo from Finland? The ToneQuest, 7(3): 11-16.

12. Wegst, U., 2006: Wood for Sound. American Journal of

Botany, 93(10): 1439-1448.

http://dx.doi.org/10.3732/ajb.93.10.1439

13. Zauer, M.; Pfriem, A., 2010: Reinforcement of Thermal-

ly Modiﬁ ed Wood for Use in Highly Stressed Compo-

nents of Musical Instruments. Proceedings of the ﬁ fth

European Conference on Wood Modiﬁ cation ECWM5,

Riga, 31-38.

14. Zauer, M.; Sproßmann, R.; Wagenführ, A., 2014: Im-

provement of the acoustic properties of European beech

to substitute hard maple for the use in musical instru-

ments. Proceedings of the Seventh European Conference

on Wood Modiﬁ cation ECWM7, Lisboa, Portugal.

Corresponding address:

Prof. Dr.-Ing. ALEXANDER PFRIEM

Eberswalde University for Sustainable Development -

University of Applied Sciences

Professorship Wood Chemistry, Wood Physics and

Chemical Engineering

Schicklerstraße 5

16225 Eberswalde, GERMANY

e-mail: alexander.pfriem@hnee.de

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Article

Feb 2006

The effect of heating on the hygroscopicity of Japanese cedar wood was investigated as a simple evaluation of thermal degradation in large-dimension timber being kiln-dried at high temperatures (>100°C). Small wood pieces were heated at 120°C in the absence of moisture (dry heating) and steamed at 60°, 90°, and 120°C with saturated water vapor over 2 weeks, and their equilibrium moisture contents (M) at 20°C and 60% relative humidity (RH) were compared with those of unheated samples. No significant change was induced by steaming at 60°C, while heating above 90°C caused loss in weight (WL) and reduction in M of wood. The effects of steaming were greater than those of dry heating at the same heating temperature. After extraction in water, the steamed wood showed additional WL and slight increase in M because of the loss of water-soluble decomposition residue. The M of heated wood decreased with increasing WL, and such a correlation became clearer after the extraction in water. On the basis of experimental correlation, the WL of local parts in large-dimension kiln-dried timber was evaluated from their M values. The results indicated that the thermal degradation of inner parts was greater than that of outer parts. Key wordsKiln drying-Steaming-Japanese cedar-Thermal degradation-Hygroscopicity

Effects of high temperature kiln drying on the practical performances of Japanese cedar wood (Cryptomeria japonica) II: Changes in mechanical properties due to heating

Article

Jan 2006

Japanese cedar wood specimens were steamed at 80°, 100°, and 120°C over 14 days, and their equilibrium moisture content (M) at 20°C and 60% relative humidity, longitudinal dynamic Young’s modulus (E), bending strength (σ max), and breaking strain (ε max) were compared with those of unheated specimens. Steaming for a longer duration at a higher temperature resulted in a greater reduction in M, σ max, and ε max. The E of wood was slightly enhanced by steaming at 100°C for 1–4 days and 120°C for 1–2 days, and thereafter it decreased. The slight increase in the E of sapwood was attributable to the reduction in hygroscopicity, while sufficient explanation was not given for a greater increase in the heartwood stiffness. Irrespective of the steaming temperature, the correlations between M and the mechanical properties of steamed wood were expressed in terms of simple curves. M values above 8% indicated a slight reduction in E and s max, whereas M values below 8% indicated a marked decrease in the mechanical performances. In addition, the e max decreased almost linearly with a decrease in the value of M. These results suggest that hygroscopicity measurement enables the evaluation of degradation in the mechanical performances of wood caused by steaming at high temperatures.

Wood for sound

Article

Oct 2006

Wegst U.G.K

The unique mechanical and acoustical properties of wood and its aesthetic appeal still make it the material of choice for musical instruments and the interior of concert halls. Worldwide, several hundred wood species are available for making wind, string, or percussion instruments. Over generations, first by trial and error and more recently by scientific approach, the most appropriate species were found for each instrument and application. Using material property charts on which acoustic properties such as the speed of sound, the characteristic impedance, the sound radiation coefficient, and the loss coefficient are plotted against one another for woods. We analyze and explain why spruce is the preferred choice for soundboards, why tropical species are favored for xylophone bars and woodwind instruments, why violinists still prefer pernambuco over other species as a bow material, and why hornbeam and birch are used in piano actions.

On the effect of heat treatment upon acoustic properties of spruce

Jan 1986
157-166

C Gadd
J D'arcy

Gadd, C.; D'Arcy, J., 1986: On the effect of heat treatment upon acoustic properties of spruce. Journal of the Violin Society of America, 7 (4): 157-166.

Herkunft, Lagerung und Präparation von Tonhölzern im Spiegel historischer Quellen

Jan 1999
23-34

K Martius

Martius, K., 1999: Herkunft, Lagerung und Präparation von Tonhölzern im Spiegel historischer Quellen. Scripta Artium 1: 23-34.

Use of wood performed by heat-treatment for musical instruments

Jan 2005
390-397

A Pfriem
A Wagenführ
G Ziegenhals
K Eichelberger

Pfriem, A.; Wagenführ, A.; Ziegenhals, G.; Eichelberger, K., 2005: Use of wood performed by heat-treatment for musical instruments. Proceedings of the Second European Conference on Wood Modifi cation, Göttingen, 390-397.

Thermally Modified Wood for Use in Musical Instruments

Abstract

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