Abstract
In a previous paper, to clarify features of the sound field of a structure-acoustic coupling system, a rectangular parallelepiped with a flexible panel at one side is analyzed. From a practical viewpoint, a parallelepiped with many flexible panels is also important. In this paper, a rectangular parallelepiped with two flexible panels in opposite sides is considered. First, experimental study is conducted. Two features worth noting are found. One is that there is in the response a fixed state, which is unaltered by a modification of the structure. The other is that the sine modal shape can exists, whose existence is confirmed in the usual structure only when its both ends are open. Then, theoretical study is made using a one-dimensional mathematical model. It is found this model can explain the features mentioned above.
