“A violinist leaves behind some of his soul in the instrument“, replied world-famous violinist Anne-Sophie Mutter in 2007 to the Swiss daily newspaper “Der Bund“, to the question, what in her opinion is the secret of a Stradivarius. The musical past of a violin contributes to the sound production of the respective player. In contrast to a musician, wood science has to ignore the influence of the muse in its research activities, and limit itself to measurable data in the evaluation of tonal behaviour. Which is what the Institute for Musical Instrument Making at the TU Dresden in Zwota and the Institute for Wood and Paper Technology of the TU Dresden do, and they also scrutinise the properties of thermally modified timber. Positive research results from Prof. Dr.-Ing. André Wagenführ, Dipl-Ing. Alexander Pfriem and Dipl.-Ing. (FH) Klaus Eichelberger provide hope for violin makers and and other branches of the music industry.
The love for music is one that reaches around the world. Many millions of musical instruments are made from wood each year. And so the shortage of high-quality wood has been worrying some in the music industry for some time now, especially as environmental activists are up in arms against the use of rare tropical woods for guitar making. Spruce wood, often used for the lid of the guitar, must have a diameter of at least 60cm, and ideally the trunk should be a metre or more in size.
Fir trees have grown calmly in the mountains for 250 to 300 years with fine and uniform growth rings, until they provide light and yet stable resonating wood for guitars, violins, violas or cellos. But this precious wood is becoming rarer and more expensive, and to complicate matters, only one in five of these old trees is suitable for instrument making, in Klaus Eichelberger’s estimation. Just increasing this proportion would be a great success for wood research.
The Institute for Musical Instrument Making in Zwota studied the question of whether the physical-technical properties of the resonating woods could be improved through a specific modification. The raw materials were prepared thermally, in accordance with the mild pyrolysis method of the company Thermoholz Austria, in three different modification stages, and compared in a variety of tests with untreated wood.
Cell changes were examined under the scanning electron microscope, the water absorption coefficient was compared and mechanical properties such as acoustic velocity or acoustic resistance, tensile strength and bending strength were recorded. A Memmert Universal oven among other things is used to determine the moisture content, in compliance with DIN EN ISO 52180. Each wood reabsorbs humidity after drying, but the research team was able to verify that thermowood does this to a considerably lesser degree than untreated woods, which can be an advantage for woodwind instruments and instruments exposed to different climates.
Moreover, the woods that have been thermally treated mildly or to a moderate degree display a larger dimensional stability, higher durability and an improved tonal behaviour, comparable to artificial ageing, without negative effects such as the brittleness of the wood having any significant influence on the quality of the instrument. Increasing the value of poor stocks of wood will initially not be possible, according to a statement from the Zwota researchers, but an enhancement of wood quality could be achieved through thermal modification, so that it presents a genuine alternative to tonewood that has aged naturally, for violin makers and guitar makers.
Today thermowood is not the prevalent material for violin makers.
