Abstract
An experimental examination of the relationship between the macrostructure characteristics and the acoustic properties of Norway spruce was performed. The macrostructure features were found to comprise the density (ρ), percentage of latewood (%LW), slope of grain (α), and angle the annual rings in a cross section (β). The main acoustic parameters of the research were the sound velocity, dynamic Young’s modulus, acoustic impedance (Z), and radiation coefficient (R). The acoustic properties for both the cross section and the longitudinal direction were calculated. Non-destructive evaluation (NDE) is the appropriate approach to define acoustic properties. Ultrasonic direct transmission and a transitory excitation method were used to calculate and compare the acoustic properties. A modal analysis was performed to predict the frequency range that corresponded to the different mode shapes. There were no significant differences between the two methods, yet an 80% reduction of the velocity, Z and R was identified between the longitudinal direction and the cross section. The equations used to define acoustic radiation according to the latewood component were defined, and strong correlations between the macrostructure and acoustic parameters were confirmed. A tight relationship was observed between the reduction of sound velocity and material density exceeding 440 kg m−3.
Highlights
The parameters and properties that define the acoustic qualities of soundboards are moisture, density, and sound speed, which are followed by modulus of elasticity (MOE), specific dynamic modulus, internal friction, radiation coefficient (R), acoustic conversion efficiency, and acoustic impedance (Z) [11,12,13,14,15,16,17,18,19,20]
Three methods were developed for the acoustic Nondestructive evaluation (NDE): ultrasonic direct transmission, stress wave, and resonance frequency vibration [22,23]
The value of the sound velocity along the L direction (VLL ) for Norway spruce is around 5350 m s−1 [35,36,37,38]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The parameters and properties that define the acoustic qualities of soundboards are moisture, density, and sound speed, which are followed by modulus of elasticity (MOE), specific dynamic modulus, internal friction, radiation coefficient (R) (acoustic constant), acoustic conversion efficiency, and acoustic impedance (Z) [11,12,13,14,15,16,17,18,19,20]. Three methods were developed for the acoustic NDEs: ultrasonic direct transmission, stress wave, and resonance frequency vibration [22,23]. The ultrasonic direct transmission method uses a higher frequency (>20 kHz ultrasonic waves) and two piezoelectric sensors [24,25]. This article focuses on the definition of the strict relationships between the macrostructure of resonance wood and its acoustic properties
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