SEAT DIP EFFECT - THE PHENOMENA AND THE MECHANISM

The phenomenon of excess attenuation due to audience seating, which is called ''seat dip effect (SDE),'' have been discussed in the case of a rather short-time interval including a direct sound and early arrivi ng sound. However, it may be expected that the effect is diminished as the time interval increases, owing to the supplement of other arrivin g sounds. The first aim of this investigation is to clarify the effect of time interval on the SDE as well as the effect of other arriving s ounds, by means of 1/10-scale model experiments, For the mechanism of the phenomenon, a clear explanation has not yet been given. The second aim is to clarify the fundamental mechanism of the SDE, For this aim, a wave-scattering theory for a periodic surface and a simple wave ref lection theory for a layered boundary surface are applied, and discuss ed in comparison with the experimental results. From this investigatio n, it became clear that the mechanism of the SDE can be easily explain ed by using these simple analytical models. (C) 1997 Acoustical Societ y of America.