AN EXPERIMANTAL STUDY ON THE ABSORPTION CHARACTERISTICS OF PERMEABLE MEMBRANE ABSORBERS ARRAY

摘要

Permeable membranes (PM), which are woven or non-woven fabrics with air permeability made from various natural or chemical fibers, are one of the attractive sound absorbing materials. They have flow resistance suitable for sound absorption purpose, and they can absorb sound energy by their acoustic resistance. In addition, PMs are lightweight, and have high designability. The simplest PM absorber is a single-leaf PM absorber (PMSG) with porous type sound absorption characteristics, in which a PM is placed in front of a rigid-backed non-locally reacting air cavity. The air cavity can be partitioned using honeycomb core to create locally reacting air cavity (PMHC). However, the two conventional absorbers have some disadvantages in their absorption characteristics. For example, PMSG has low field incidence absorption coefficient at lower frequencies due to the effect of non-locally reacting air cavity whilst PMHC has low field incidence absorption coefficient at notch frequencies due to the locally reacting air cavity. This paper presents PM absorbers array (PMAR) to overcome the above deficiency of PMSG and PMHC. PMAR uses multiple locally reacting air cavities with different depths so that each cavity has different notch frequencies. The purpose of this paper is to show the reverberation absorption characteristics of PMAR over the two conventional absorbers. The simple construction method of PMAR using honeycomb core is also presented. The results of reverberation absorption characteristics of PMAR fabricated using nine PMs less than 1 mm thickness with different flow resistance and surface density demonstrated that PMAR has higher absorption coefficient at wider frequency ranges over the two conventional absorbers.