It is well known that wall impedance essentially determined how sound wave transmits from one place to another. The wall impedance is related with wall’s dynamic properties; for example, its mass and stiffness characteristics. It is noteworthy, however, that the wall impedance, in the strict sense, is also function of spatial characteristics of two spaces separated by the wall. In this paper, we have attempted to see how two separated spaces communicate each other. In other words, how the acoustic characteristics of two spaces is really affected by the wall impedance. Especially, we have studied the case of which has the wall that separates one space that is highly reverberant and the other one that is unbounded, therefore there is no reflection. This study explains how reverberant room, in fact this is not necessarily to be a room, any space that is dominated by reverberant sound field can be considered sends sound waves to outside.