The orifices in thick microperforated panels (MPPs) are normally straight holes. Although the increase in thickness extends application field of MPPs, the eventually change of acoustic impedance leads to the decline of absorption coefficient. One way to improve this deterioration is to have variable axial section in thick MPPs. In this paper, varying section MPP molded by tapered and step-shaped molding core were prepared by using epoxide resin, and their acoustic characters were measured. Results showed expansion of absorption band in varying section MPP. Compared with conventional straight hole MPP, the absorption frequency range extended from 300~700Hz to 310~830Hz, and average absorption increased from 0.45 to 0.54 for tapered section MPP.

MPPs are typically made of a thin metal or plastic panel. However, thin limp panels are generall not suitable as an interiornish of room walls because they do not have sucient strength, which prevent spractica lapplication of MPPs as an interiornish of roomwalls. When we put the air, water, polyvinyl alcohol and wool fiber into the pores of the thick microperforated panel respectively and the epoxy resin panel have a porosity of 7%, 10mm thick and the pore is 1mm in diameter. Measurements of the sound absorption characteristics of microperforated panel with those above material have been carried out in the Pulse 3560 and 4206 made in B&K company. The result show that the absorption coefficient of sound is better when the wool fiber’s number is 53 per pore and the depth of the back air cavity is 20mm than air in its holes. The peak value of sound absorption coefficient is about 0.94 when the resonance frequency is about 956, the frequency from 612Hz to 1600Hz all have the absorption coeifficien above 0.5.