Effect of porous material compression on the sound transmission of a covered single leaf panel

In this paper, the authors examine the effect of compressing a poroelastic fibrous layer lined with an isotropic plate on the sound transmission loss (TL). For this purpose, a 2-in. thick fibrous material and two isotropic plates with critical frequencies around 2300 Hz and 9700 Hz were used. The transfer matrix method was applied and the porous layer was assumed to have either a rigid, limp or elastic frame. Current models of compression are outlined, and measurements of the airflow resistivity as a function of compression show that these models are suitable only for low compression rates. TL predictions are compared next to experimental data in a range between 100 Hz and 10000 Hz for three compression rates, corresponding to 0%, 20% and 50%. The fibrous is uniformly compressed over 100% of its surface. Our experiments showed that compression reduces the TL by a maximum of 5 dB for a 50% compression, mainly at the mid-frequency range, around 800 Hz. This is due to a resonance in the thickness of the porous material, increasing the radiation efficiency of the structure at mid-frequencies. Moreover, reduction of the porous thickness and increase of the airflow resistivity with compression are the variations influencing the most the TL of the structure. These trends were also detected with the limp and rigid frame models but with a lower degree of accuracy compared to the elastic frame model.