Tunable Acoustic Properties Using Different Coating Systems on Resonance Spruce Wood

Abstract

The study investigates the effect of the type of varnish and the number of layers on some acoustic properties of the resonance spruce in combination with the changes produced in some physical, morphological, and chemical properties of wood. In addition to color changes and surface chemistry, the surface roughness and morphology are modified by the thickness of the varnish film, 10 layers being optimal from this point of view, as well as the oil‐based finish. The sound absorption coefficient increases with the number of varnish layers and varies with the sound frequency range, varnish type, and wood quality, all contributing to the acoustic tunability. For example, for a sound frequency of 1.5 kHz, it is observed that the oil‐based varnish with 5 and 10 layers contributes to a full sound, while the alcohol varnish, due to a lower absorption coefficient for this frequency, can lead to some nasal sounds. Applying more than 10 layers of varnish does not improve the sound performance as it will soften the sound in an oil‐based finish and make the sound too sharp in the case of alcohol–varnished wood.

11th Hardwood Conference Proceedings

“…The evaluation of the propagation speeds of Lamb waves using ultrasound method, applied on thin maple wood plates varnished with alcohol varnish, respectively oil varnish, carried out by Faktorova et al (2024), highlights that the increase in the number of varnish layers, regardless of the type of varnish , led to the decrease of the anisotropy ratio between the longitudinal and radial directions. Stanciu et al (2024) studied the acoustic absorption of spruce wood samples varnished with alcohol varnish and maximum oil varnish, observing that the type of varnish changes the frequency at which the acoustic absorption is maximum. Thus, in the samples varnished with oil varnish, the acoustic absorption is not influenced by the varnish film, compared to the samples varnished with alcohol where the maximum coefficient of acoustic absorption occurs at different frequencies for the two parts of the samples: the unvarnished face absorbs the sounds with the maximum frequency in the 2-3 kHz range, and the varnished face absorbs sounds at frequencies higher than 4-5. kHz.…”

Analysis of the Anisotropy of Sound Propagation Velocity in Thin Wooden Plates Using Lamb Waves

“…Based on these considerations, currently, the most well-known types of varnishes used for maestro- and professional-level musical instruments are those with an oil-based solvent and those with an alcoholic solvent (spirit) [ 32 , 33 , 34 , 35 ]. Not only is the chemical composition of the surface treatment important but also the thickness of the varnish film and the varnish–wood interface, aspects highlighted in studies [ 36 , 37 , 38 ]. The type of varnish and its thickness correlated with the number of layers applied in the finishing process influence the tonality of the musical instrument as a result of not only the difference in stiffness between the wood and the varnish film but also as an effect of the increase in the mass of the layered material (wood–varnish) [ 31 , 32 , 38 ].…”

“…Not only is the chemical composition of the surface treatment important but also the thickness of the varnish film and the varnish–wood interface, aspects highlighted in studies [ 36 , 37 , 38 ]. The type of varnish and its thickness correlated with the number of layers applied in the finishing process influence the tonality of the musical instrument as a result of not only the difference in stiffness between the wood and the varnish film but also as an effect of the increase in the mass of the layered material (wood–varnish) [ 31 , 32 , 38 ]. Thus, in the presented study, spruce and maple wood samples covered with a number of layers of lacquer were analyzed according to the procedures applied at a violin factory (5, 10, and 15 layers).…”

“…According to [ 36 , 38 ], to compare the mass changes of the spruce and maple boards before and after surface treatments (VS varnish system, UV exposure, and salt fog exposure), the changes were evaluated as area mass loading (AML) calculated based on mathematical relation (1): where is area mass loading induced by treatment (g·m −2 ); —the final mass of the treated wood; —the initial mass of the wooden sample; b —the width of the plate; and l —length of the plate [ 36 , 38 ].…”

“…where 𝐴𝑀𝐿 is area mass loading induced by treatment (g•m −2 ); 𝑚 -the final mass of the treated wood; 𝑚 -the initial mass of the wooden sample; b-the width of the plate; and l-length of the plate [36,38]. The samples were obtained by cutting radially longitudinally from the boards, which, after natural drying, were conditioned in a drying chamber up to a moisture content of 6-8%.…”