Study On Vibration Property Of Spruce Resonance Board And Acoustical Quality Evaluation Of Piano

The piano acoustical quality is decided by the soundboard to a great extent. In the producing, the technician evaluates and chooses the wood for piano soundboard subjectively for the moment. It is inefficient, large error, and insufficiency of the scientific foundation. It does not satisfy the requirement to produce the excellent piano soundboard in the condition of volume-produce.In order to establish the objective selection method of wood selection for piano soundboard and objective evaluation method of vibration property of piano resonance board, track-study of vibration properties from the wood used for resonance board 1) of Picea glehnii, Picea jezoensis, Picea likiangensis var. linzhiensis, and Picea sitchensis, resonance board 2), to soundboard 3), until the acoustical quality of piano were studied.The comprehensive vibration properties of the samples of every species were analyzed and differentiated respectively by the comprehensive coordinate method and comprehensive marking method. According to the results of differentiation, two groups of samples used for producing the resonance boards in every species were selected respectively, and the distinction between the both groups was obvious (the No.1 and No.2 groups of samples respectively, correspond to the No.1 and No.2 piece of resonance board, correspond to the No.1 and No.2 piano). The vibration properties of resonance board were analyzed base on the vibration theory of thin plate. After the pianos were producing, the acoustical qualities of pianos were evaluated by the subjective method, objective method, and psycho-physiological index method. On the basis of the comprehensive analysis of the correlation between vibration properties of the resonance board and the acoustical quality of pianos, the objective evaluation method of the resonance board of piano and the objective selection method of wood used for soundboard were established.The main research contents and results were summarized as follows:(1) On the basis of studying exploringly on the vibration properties measurement of full - size wood samples, the vibration properties of full-size wood used for resonance board of piano were measured. The comprehensive vibration properties of samples of Picea glehnii, Picea jezoensis, Picea likiangensis var. linzhiensis, and Picea sitchensis were analyzed and differentiated by comprehensive analysis methods. And finally, two groups of samples were selected for producing the resonance board of piano, and that the distinction of vibration properties between the No.1 groups and the No.2 groups was obvious in every species.(2) The samples of wood used for resonance board were glued to resonance board. The foundation theory of vibration of piano resonance board was analyzed, and the frequency equation of free vibration was acquired. The MOE, velocity of longitudinal wave of resonance board on the x (MOE_x, VL_Lx) and y (MOE_y, V_Ly) direction were computed by the frequency equation and longitudinal wave transmittal equation. The results were: the MOE_x, MOE_y, VL_x, V_Ly of the No.2 piece of resonance board (correspond to the No.2 group of wood samples) are larger than the No.1 (correspond to the No.1 group of wood samples) in every species; for all resonance boards, the MOE_y, V_Ly are larger than MOE_x, V_Lx. The mechanical, properties of the 45°grain samples in the edge of the resonance board were analyzed, and the results were same to the resonance board.(3) The soundboard is the resonance board that the ribs were glued on it. The influence of ribs on the sound transmit velocity of piano resonance board was analyzed. The result shows that the ribs can enhance the sound transmit velocity on the radius direction of resonance board. The response time of vibration on the radius direction is near to that on the longitudinal direction. That is because the ribs enhance the sound transmittal velocity on radius direction of resonance board.(4) The acoustical quality of the pianos was evaluated by the subjective and objective method. The experts of subjective evaluation were engaged in piano performance and education many years. The indexes of objective evaluation were loudness, sound length, dynamic range, and tone. The results of evaluation were: the acoustical quality of the No.2 piano was more excellent than the No.1 piano in the same species.(5) The influence of the piano music on psycho-physiological reaction (the main indexes are Heart Rate Variability, Blood Pressure Variability, Skin Temperature, and Respiration Frequency) of the subjects who are undergraduate without the background of musical training were analyzed. Compared with the resting state, the subjects' physiological reaction was changed when they enjoyed the piano music. The subjects' sympathetic nerves activity decreased, and the parasympathetic nerves activity increased, but the equilibrium was not broke. The synthetical presentation was that the activity of autonomic nervous system was weakening, and the subjects were more comfortable than they were resting. Then the differentiation of the influence of two pianos music of the same species on the subjects' physiological reaction was analyzed. The results show: when the subjects were enjoying the music of the No.2 piano the sympathetic nerves activity of the subjects decreased, the parasympathetic nerves activity increased, and they were more comfortable than that the No.1 piano of the same species.(6) The correlation between the vibration properties of resonance board (MOE_x, MOE_y, V_Lx, V_Ly), MOE of the 45°grain sample in the edge of the resonance board (MOE_45x, MOE_45y), response time of vibration of soundboard (T_L—time of longitudinal direction, T_R—time of radius direction) and the score of subjective evaluation, indexes of objective evaluation of piano acoustical quality were analyzed. The correlation between subjective evaluation score, objective evaluation indexes and the vibration properties in the y-direction of resonance board were more significant than that in the x-direction. That may be related to the strings array frame. Because the strings axis in high and intermediate frequency region is near parallel to y-direction and the angle between strings axis and y-direction in low frequency region is smaller than that between strings axis and x-direction of the soundboard. The correlation between subjective evaluation score, objective evaluation indexes and the response time of vibration of soundboard in the radius direction were more significant than that in the longitudinal direction of wood. So, the acoustical quality of piano is improved with the MOE (MOE_x, MOE_y), velocity of longitudinal wave of resonance board (V_Lx, V_Ly) increased, especially in the y-direction. If the discrepancy between T_L and T_R is abated with T_R reduced, the piano acoustical quality is improved.(7) The objective evaluation method of wood used for piano resonance board is: the MOE of the resonance board or the 45°grain sample in the edge of the resonance board is measured, especially the y-direction(MOE_y, MOE_45y); And the velocity of longitudinal wave transmittal, or response time of vibration of soundboard is measured, especially the y-direction velocity (V_Ly) or the response time of vibration in the radius direction of the soundboard (T_R).(8) The objective selection method of wood used for piano soundboard is: the comprehensive vibration properties of wood used for piano soundboard are computed by comprehensive coordinate method and comprehensive marking method, and the indexes include wood longitudinal and radius (or 45°direction of grain) vibration properties.