Study On The Change And Mechanism Of Acoustic Properties Of Musical Instrument Wood Treated With Different Temperature Andhumidity

Music,which is the dazzling diamond of art crown,do make great influence on human civilization.In order to promote the development of music,the research on the music producer,musical instruments,is the key to discover the secret of music.In this study,the comparasion on acoustic vibration performance and pronunciation stability were studied among four commonly used wood species for traditional musical instruments,which were Paulownia sp.,Catalpa sp.,Cunninghamia lanceolata and Picea sitchenrsis.The reasons are analyzed according to the perspective of anatomical structure,pore structure and chemical composition,in order to comprehensively understand the rules of material selection in the manufacture of musical instruments.In addition,two methods of dry-wet cycle treatment and high-temperature heat treatment were used for artificially accelerated aging to explore the actual impact on the improvement of wood acoustic performance and its change mechanism,and provide theoretical basis for the improvement of acoustic performance and pronunciation stability of wood for musical instruments.(1)Traditional Chinese musical instruments often use paulownia and fir to make soundboards,and catalpa for bottom plates.While for Western musical instruments,spruce is often used for making soundboards,which were reflected at the performance of acoustic vibration.Among the four wood species,Paulownia sp.,C.lanceolata and P.sitchenrsis have good acoustic vibration performance,but the acoustic vibration performance of Catalpa sp.(E/ρ19762.42Mpa,R8.55m~4/kg·s,v 4443.07m/s,ω2.31)is relatively poor.When it comes to the reason based on the anatomical structure for great performance on acoustic vibration.The results indicated theat tracheids and wood rays are uniformly arranged in fir and spruce,with larger ratio of length to width of tracheid(C.lanceolata:80.19;P.sitchenrsis:95.23)and longer tracheids(C.lanceolata:3433.99μm;P.sitchenrsis:3433.99μm).Paulownia sp.has good acoustic vibration performance,mainly due to its large ducts and rich parenchyma.The abundant inclusions and thick wood fiber cell walls are the main reasons for the relatively poor acoustic performance of Catalpa sp.(2)After the dry-wet cycle treatment,the acoustic vibration performance and pronunciation stability of each wood species(Paulownia sp.,Catalpa sp.,C.lanceolata and P.sitchenrsis)were effectively improved.And it is the most effective for improving the acoustic vibration performance of Paulownia sp.Its specific dynamic elastic modulus,sound radiation quality constant,and sound speed are increased by 30.78%,46.09%,and 14.40%,respectively,and the acoustic impedance is decreased by 10.65%.Furthermore,it was found that the dry-wet cycle treatment did not change the chemical composition of the wood.However,the pore structurehas changed,and the total pore volumehas decreased(20.56%for Paulownia sp.,36.77%for Catalpa sp.,25.85%for C.lanceolata,and 50%for P.sitchenrsis).The reduction of cell wall pores made it difficult for water vapor to enter,and the saturated water absorption of mono-layer molecules decreases,which reduces the equilibrium moisture content of wood and improves pronunciation stability.(3)High temperature heat treatment was able to effectively improve the acoustic vibration performance of wood.With the increase of heat treatment temperature,the acoustic vibration performance of wood tends to increase.In addition,the high temperature heat treatment reduced the hygroscopic properties of the wood and improved the pronunciation stability,and with the increase of the treatment temperature,the pronunciation stability improved.On the whole,the acoustic performance of each wood species had been improved,and the acoustic performance achieve the best under 220℃(final temperature)and 2h(holding time).The analysis indicated that the relative crystallinity of each wood species was generally improved under different temperature treatments(the maximum increase of Paulownia sp.is 12.07%,the maximum increase of Catalpa sp.is 26.06%,the maximum increase of C.lanceolata is 9.69%,and the maximum increase of P.sitchenrsis is 14.75%).In addition,high temperature heat treatment reduced the micropores of various wood species,and the micropores did disappear completely under treatment at 220°C,which restrained the water vapor.The hemicellulose of all wood species were degraded to different degrees after treatment at different temperatures,and the degradation degree reached the maximum after treatment at 220°C,which decreased by 59.91%(Paulownia sp.),53.37%(Catalpa sp.),43.43%(C.lanceolata),and 24.99%,respectively.(P.sitchenrsis).Hemicellulose has good hygroscopicity for its rich hygroscopic groups(hydroxyl groups).Therefore,the degradation of hemicellulose reduces the hygroscopicity of wood.This reveals another important reason why heat treatment reduces the hygroscopicity of wood.(4)The intensity of dry-wet cycle treatment is small and no chemical change occurs,and the improvement of its acoustic vibration performance is mainly attributed to the decrease of equilibrium moisture content.The improvement of pronunciation stability is due to the reduction of micropores and mesopores in the cell wall,the reduction of the total pore volume,making it difficult for water vapor to enter,and the saturated water absorption of monolayer molecules,which reduces the equilibrium water content and improves the pronunciation stability.The strength of high temperature heat treatment is large,and chemical changes have occurred.The decrease of absolute dry density and the increase of relative crystallinity are the main reasons for the improvement of acoustic vibration performance.The improvement of pronunciation stability is due to the reduction of micropores on the cell wall,which reduces the hygroscopicity.