Effect of coating with Shellac on acoustic properties in white mulberry wood

In this study the effect of coating with lacquer (Shellac) on acoustic properties by forced flexural vibration in free-free beam in white mulberry (Morus alba) and walnut (Juglans regia) have been investigated. For this purpose, the samples of both species with dimensions of 2 × 15 × 140 (length, width, height) were prepared. The samples of both species for integrated humidity were kept in climatic chamber for three week in climatic chamber (20 ± 2C0 and 65 ± 5 % rH) and then the first step of forced vibration test for measure basic properties of the both test samples were performed on them. Aftter that the samples of both species were coated by lacquer and after integrated humidity in samples to assess the effect of lacquer on acoustic properties forced flexural vibrations test was performed on them again. The results showed equal variations in the specific gravity in both coated species in mulberry and walnuts samples. The modulus of elasticity, acoustic coefficient and acoustical conversion efficiency values after coating were reduced in both that drop in values in mulberry more than walnut species.The reason of this results caused with variations in the frequency and specific gravity of the test specimens in both species that variations in frequency in mulberry more than walnut species. Damping vibration values under the influence of coating was increasing in both species that's results obtained because the different influence of alcohol in withdrawal extractives in mulberry and walnut species and different nature and role of these substances in each species that mulberry that this factor values referred to in mulberry species was over than walnut species because of the different nature of the extractives in each species.