Advanced passive treatment of low frequency sound and vibration

It is well known that standard poroelastic materials and viscoelastic damping materials are ineffective at reducing low frequency sound and vibration. This paper overviews two new treatments developed at Virginia Tech which attempt to address this problem. HG material consists of poroelastic material with embedded multiple small masses. The masses combine with the natural elasticity of the poroelastic material matrix to create multiple embedded vibration absorbers with a range of tune frequencies in the low frequency region. The embedded masses are found to significantly increase the low frequency transmission loss and absorption of the poroelastic material. DVAs are vibration absorbers whose active mass and spring are spread over a large area while still maintaining a viable reactive damping effect at low frequencies. DVAs are found to provide global reduction of low frequency vibration of structures in a compact, lightweight configuration. DVAs are also observed to provide mid to high frequency damping most likely to air squeeze damping effects. The paper will overview the concepts, development and testing of both devices. Applications of the new treatments to realistic structures will be considered.