Study of sound transmission through single- and double-walled plates with absorbing material: Experimental and analytical investigation

In this work, the authors study sound transmission through single- and double-walled thin rectangular plates of finite extent, theoretically and experimentally. For this purpose, statistical energy analysis (SEA) is developed to predict the sound transmission loss of the plates. The essential SEA parameters, modal density and loss factors, are calculated and expressions for the sound transmission loss based on the SEA method are presented for both single- and double-walled plates. In order to validate the analytical results obtained for the transmission loss, an experimental setup was constructed including two reverberant chambers and a plate structure. The plate was placed between two rooms and the rooms were made in such a way that the sound waves propagate from the source room to the receiving room only through the rectangular panel. The sound transmission losses evaluated from the SEA models are compared with the experimental results which show good agreement. Three experimental methods were used to measure the transmission loss: The transmission suite method, a sound intensity method with a direct approach and a sound intensity method with an indirect approach. It is shown that the sound intensity method with a direct approach is more accurate than the other methods. This latter method could predict the critical frequency of the plate with only 0.5% error, whereas the other two methods had an error of more than 5%. The effects of using absorbing materials with single-walled plates were investigated experimentally and the effects of filling the cavity of double-walled plates with absorbing materials were also studied analytically. It was found that filling the cavity of the double-walled plate with lightweight absorbing material such as fiberglass increases the sound transmission loss at the critical frequency from 39dB to a value slightly more than 53dB. Also about 45dB improvement in noise reduction is achieved in comparison to a similar single-walled plate.