Thermal Modification of Spruce and Maple Wood for Special Wood Products

Abstract

This article presents a proposal of thermal modification of Norway spruce and sycamore maple for special wood products, mainly for musical instruments. Selected physical and acoustical characteristics (PACHs), including the density (ρ), dynamic modulus of elasticity along the wood grain (EL), specific modulus (Esp), speed of sound along the wood grain (cL), resonant frequency (fr) and acoustic constant (A), logarithmic decrement (ϑ), loss coefficient (η), acoustic conversion efficiency (ACE), sound quality factor (Q), and the timbre of sound, were evaluated. These two wood species were chosen regarding their use in the production or repair of musical instruments. For the thermal modification, a similar process to the ThermoWood process was chosen. Thermal modification was performed at the temperatures 135 °C, 160 °C and 185 °C. The resonant dynamic method was used to obtain the PACHs. Fast Fourier transform (FFT) was used to analyze the sound produced. The changes in the observed wood properties depended on the treatment temperature. Based on our results of all properties, the different temperature modified wood could find uses in the making of musical instruments or where the specific values of these wood characteristics are required. The mild thermal modification resulted in a decrease in mass, density, and increased speed of sound and dynamic modulus of elasticity at all temperatures of modification. The thermally modified wood showed higher sound radiation and lower loss coefficients than unmodified wood. The modification also influenced the timbre of sound of both wood species.

Aging of Wood for Musical Instruments: Analysis of Changes in Color, Surface Morphology, Chemical, and Physical-Acoustical Properties during UV and Thermal Exposure

“…The principle of the ultrasound (US) measurements is presented in Figure 4 [ 17 ]. The density of each plate was also determined in each stage of the experiment, and the longitudinal and radial modulus of elasticity was calculated in accordance with the calculation relationship mentioned by [ 26 ]. The mean (MV) and standard deviation (SD) values of the measured parameters were recorded before and during exposure to temperature and UV.…”

“…Several studies have addressed the problem of the photodegradation of wooden surfaces due to UV and thermal radiation, but very few of them have analyzed the acoustic and physical changes produced in the resonance wood used for musical instruments [ 17 , 23 , 24 , 25 , 26 , 27 ]. Noguch et al 2012 [ 17 ] and Obataya 2017 [ 24 ] observed an increase in the stiffness of naturally aged wood by approximately 38% in 121-year-old wood, after which a decrease was observed with increasing aging time.…”

Avaliação das propriedades acústicas de mogno africano (Khaya ivorensis) submetido a tratamento térmico em estufa e autoclave

“…A eficiência da conversão acústica (ECA) está diretamente associada à eficiência da conversão da energia de vibração do material em energia acústica. Essa grandeza é útil para mostrar os efeitos de grupo, por exemplo, o efeito da radiação acústica e da atenuação acústica juntos [12,23]. A ECA comumente associa a razão entre o coeficiente de radiação acústica pela atenuação acústica apresentada pelo material da amostra (Equação 5).…”

“…Resultados semelhantes foram relatados por DANIHELOVÁ et al [23] que submeteram madeiras de Picea abies (L.) Karst. e Acer pseudoplatanus, L. a processos térmicos utilizando a técnica ThermoWood ® e tratamentos a 135, 160 e 185 °C.…”

New Challenges in Wood and Wood-Based Materials II

“…The desire of musical instrument manufacturers to reduce the negative characteristics of raw material wood through special modification processes has existed for a century now [ 43 , 44 ]. In research by Danihelova et al [ 45 ], the authors investigated the suitability of thermally modified (ThermoWood process) Norway spruce and sycamore maple for special wood products, mainly for musical instruments. Selected physical and acoustical characteristics (PACHs) including density, dynamic modulus of elasticity along the wood grain, specific modulus, speed of sound along the wood grain, resonant frequency, acoustic constant, logarithmic decrement, loss coefficient, acoustic conversion efficiency, sound quality factor and the timbre of sound were evaluated.…”