As far as a cylindrical cavity is concerned, the wave pattern
formed in the sound field behind the MPP may possibly deteriorate
the dissipation capability of the MPP, and the circumferential and
longitudinal modes are identified to be responsible for this degradation
in the numerical analysis. To avoid this, the original backing
cavity is divided into sub-cavities with partitions installed in two
ways: (1). 9 rings are placed behind the MPP to prevent the formation
of longitudinal wave pattern in the MPP backing sound field