Sound insulation properties of sandwich structures on glass fiber felts

This paper focuses on three types of glass fiber felt sandwich structures to identify the optimal sound insulation structure. Air flow resistivities of glass fiber felts are 6633 Pa center dot s/m(2) (Loose), 19579 Pa center dot s/m(2) (Mid) and 42724 Pa center dot s/m(2) (Dense), respectively. The three types of sandwich structures are dense-mid-loose (DML), mid-loose-dense (MLD) and loose-dense-mid (LDM), respectively. Sound transmission loss is determined by an impedance tube method and the structure morphology is examined by the optical microscope. The results show that sound insulation property is affected by both the sound incident direction and composite structure. The optimal sandwich structure is MLD with the incident surface being M. The composite structures with the best and worst sound insulation are compared at the frequencies of 630 Hz, 1000 Hz, 2000 Hz and 3000 Hz. The growth rates of sound insulation are 7.4 %, 19.0 %, 15.4 % and 10.5 %, respectively. The sound transmission is also calculated by a simple numerical model which agrees with the experimental results well.