In this diploma, the change of acoustic properties over time of spruce (Picea abies (L.) Karst.) and maple (Acer pseudoplatanus (L.)) lamellae with the dimensions of 400 mm × 75 mm × 3 mm, and treated with a cellulose-nitrate or polyurethane coating, were investigated. The acoustic properties were investigated by studying the frequency response of the flexural vibration mode after dynamic-mechanical excitation of the lamellae. The tests were first conducted on untreated lamellae and repeated seven times on treated samples – four times a week apart, and three times a month apart. After the application of surface coatings, the density of the lamellae increased significantly, and the sound damping (tanδ) rose sharply. A drop in resonant frequency (f), the dynamic modulus of elasticity (E) and other acoustic properties (ACE, RACE, Esp) was also detected. In the process of ageing, the hardness of both cellulose-nitrate and polyurethane coatings rose by about 50% up to 120% in 1.5 months. The hardening process of the coatings influences sound damping (tanδ), lowering it by about 50% in 1.5 months, with measurements close to those obtained on lamellae without a surface coating. The dynamic modulus of elasticity did not change much with time, as it stayed well within the ±10% range. The reduction of sound damping (tanδ) as the coatings aged caused a rise in the other acoustic properties (ACE, RACE, K) that are directly dependent on tanδ. The aforementioned acoustic properties stabilized and reached values comparable to untreated lamellae in 1.5 months.
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