Abstract
Various structures and materials have been developed to improve the sound insulation, and a lot of experiments have been conducted to verify these things. For reason that this method is time-consuming, a simulation using finite element method for a one-dimensional long and narrow acoustic tube has been proposed. However, the calculation result does not agree with the theoretical value and needs to be corrected. This acoustic tube has an incidence side and a transmitted side with a test piece in between. The sound pressures in front of and behind the test piece are obtained to calculate the transmission loss as the sound insulation characteristics of the test piece. In this model, the end of the transmitted side is used to set as a reflective boundary. The reason for the difference from the theoretical value is that the sound pressures obtained by FEM include both forward and backward waves. According to the definition, the sound insulation is calculated using the forward sound pressure at both sides by setting the end of the transmitted side as a non-reflective boundary. In this paper, to generalize this method, it is theoretically examined that the FEM sound pressure can be accurately separated to the forward and backward wave pressures from Helmholtz's equation. Then, the validity is confirmed by evaluating the sound insulation characteristics of the flat plate with theoretical values. In addition, the sound insulation characteristics of the plates with single core are compared with that of equal weight flat plate, and the effect for the sound insulation characteristics by the aspect ratio is examined.
