Implementation experiment of a honeycomb-backed MPP sound absorber in a meeting room

Abstract

This paper presents the absorption performance of honeycomb-backed microperforated panel (MPP) absorbers, which are needed to improve the acoustics of an existing 91 m3 small meeting room where the reverberation time is over two seconds from 250 Hz to 2 kHz, for comfortable speech communication. In Japan, MPPs are difficult to use combustible materials, particularly, panels with holes for interior walls owing to fire regulations. Therefore, we implemented the MPP absorber as an additional attachment that can be hung on walls and ceilings. First, the absorption characteristics of the MPP absorber were designed to reduce reverberation times at mid-frequency using an electroacoustical equivalent theory. Then, a wave-based finite element method simulation was used to determine the absorber placement. Absorption coefficients of the honeycomb-backed MPP absorber were also measured in an irregularly shaped reverberation chamber. Finally, the effect of the installed MPP absorbers was checked by acoustic parameter measurements. As a result, we observed that the reverberation time was reduced under 1.5 s in all frequencies, the equivalent absorption area doubled, the early decay time values were also reduced from 2.7 s to 1.0 s at 1 kHz, the clarity (C50,mid) increased by more than 5 dB, and the speech transmission index (STI) value increased from 0.55 to 0.67 by one rank up.