Studies on seat-dip effect with 3D FDTD modeling

According to the literature, the seat dip effect creates a valley in the frequency responses of the direct sound and some early reflections in concert halls. The low frequencies are attenuated up to 20 dB between 100 and 500 Hz due to the sound passing over seating at near grazing incidence. The seat dip effect includes several phenomena due to the wave nature of sound, such as diffraction and scattering. In this paper we simulate several stage and seat configurations with 3D FDTD modeling. The modeling results are shown to be in close agreement with the simulated and measured data presented in the literature. However, the main point of the paper is to analyze and visualize how the low frequency energy is propagating in concert halls. The seat dip effect attenuates the low frequencies of early sound at the listening position despite that the seats are not always absorbing the energy. In fact the energy is directed to other directions and the attenuation of low frequencies in the listening position is only a local phenomenon. The visualizations let us discuss what other consequences of the low frequency sound, redirected by the seats, have to the concert hall acoustics.