Calculation of Acoustical Characteristics of the Sound Insulation Pad by Micro Perforated Membrane Theory

PE (polyethylene) membranes are widely adopted in sound insulation pads inside vehicle. However, there are few studies on the acoustical effects of these inserted membranes. This study focuses on these effects.

Frequently sound insulation is made up of two layers of felt (a pad made of cotton or synthetic fiber), separated by a PE membrane. The normal incidence sound absorption coefficient and sound transmission loss for this type of insulation construction were calculated through the micro perforated membrane theory and the analytical model (NOVA) which is based on Biot theory. Impedance tube measurement was used to derive the poroelastic properties needed to utilize these models. Comparison between the calculated and measured results showed that the absorption coefficient obtained from the micro perforated membrane theory was closer to the measured value above 3 kHz. And that calculated using NOVA was closer to the measured value below 3 kHz. The transmission loss calculated through NOVA was much closer to the measured value. But the shape of the transmission loss curves calculated through micro perforated membrane theory more closely matched that of the measured curves. The results calculated both through the micro perforated membrane theory and Biot theory didn't match the measured result well. Test errors and theory assumptions are likely causes. Modeling improvements, and enhanced test techniques will improve agreement between test and predicted data.