Sum K., Peng S.

A sound absorber that consists of a few different microperforated panel subabsorbers connected in parallel is constructed to control noise due to plane waves in an air duct. The combined effects of these parallel subabsorbers on the bandwidth and magnitude of sound absorption coefficient of the sound absorber are studied. It is shown that the bandwidth and the magnitude are reciprocally related, where the increase of one parameter will lead to the decrease of another. When two different parallel subabsorbers are used, the absorption coefficient can exceed 0.5 over three to four octave bands. When three different parallel subabsorbers are used, the absorption bandwidth can cover up to six octave bands. Results also show that the acoustical performance starts to deterioriate when more than three parallel subabsorbers are used. However, parallel subabsorbers have two main advantages over series subabsorbers that have been investigated. Firstly, each parallel subabsorber can be easily and independently tuned to achieve the best absorption of the sound absorber, but series subabsorbers are dependent on each other and difficult to tune. Secondly, given the same performance and facing size of the sound absorber, parallel subabsorbers occupy less space than series subabsorbers in terms of the air space depth. This paper provides an understanding of the characteristics of parallel microperforated panel subabsorbers and their application for noise control in ducts.