Numerical simulation of floor impact sound by using finite-difference time-domain method

The floor-impact sound transmission characteristics through floor structures are of great importance from the viewpoint of quality of sound environment. The sound insulation performance of the floor structure is commonly evaluated based on the sound pressure levels, which are measured by exciting the surface of the floor with various kinds of devices suitable for each purpose of the sound insulation evaluation. To obtain the sound insulation performances of heavy- and light-weight impact sound, the bang machine, impact ball, and tapping machine are utilized as the devices for excitation. Then, the measured and evaluated results by using these excitation methods greatly depend on the time and frequency characteristics of the excitation force itself. The structure-borne sound transmission characteristics can also be numerically predicted by using the SEA, FEM, and FDTD. However, in the present situation, the numerical modelling of the excitation characteristics should require more investigation to be incorporated into such a discrete wave-based numerical prediction of vibration characteristics. To investigate the simulation method of the time and frequency characteristics of the vibroacoustic transmission between the floor structures, the collision between the free-fall mass and the elastic plate-like structure are modelled by the one degree-of-freedom model structured on the discrete wave-based numerical analysis of bending vibration with finite-difference timedomain (FDTD) method. In the present paper, as the basic study, the excitation characteristics of the generally-used devices of the impact ball, bang machine, and tapping machine are simulated, and are applied to a numerical case study targeting at prediction of the impact sound pressure levels inside a wall-type concrete structure.