Abstract
In previous papers, to clarify features of the sound field of a structure-acoustic coupling system, a rectangular parallelepiped with one or two flexible panels are analyzed. From a practical viewpoint, a parallelepiped with flexible panels and with some additional masses is also important. In this paper, a rectangular parallelepiped with a flexible panel and with an additional spring mass system is considered. First, experimental study is conducted. Two features worth noting are found. One is that such mode exists, in which the flexible panel does not vibrate. The other is that a fixed state, whose existence is confirmed in the previous papers can be removed. Then, theoretical study is made using a one-dimensional mathematical model. It is found this model can explain the features mentioned above.
