In this paper, the numerical solution of the statistical chains of matrix B is successfully used to calculate the sound intensity field in audio rooms. Here we use B-chain techniques as a real breakthrough with the time-dependent sound field problem in 3D geometric space. We offer the appropriate design of audio rooms via an example of a cuboid pieces. We also show that B-chain techniques can produce rigorous statistical proof of Sabines' imperial formula for reverberation time in audio rooms. In addition, the definition of so-called statistical weights of geometric shapes is introduced and found to be effective in solving double and triple integration as well as sound diffusion transfer equation in audio rooms.