Transmission of sound across a trusslike periodic panel; 2-D analysis

Transmission of sound across a 2-D trusslike periodic panel in contact with an acoustic fluid on both its faces is analyzed. Elastic frequency response of the panel made of repeated cells is expressed using transfer matrices of the unit cell, and acoustic pressure of the fluid is expressed using a source boundary element method. Transmission loss (TL) of a panel is computed for two geometries and compared with measurements. These comparisons reveal differences that result from attenuation zones due to periodicity along one axis of the panel and response that is predominantly along the other axis. Conditions under which these differences disappear are explained. A nondimensional parameter, including the ratio of sound speeds in solid and fluid and the ratio of panel length to radius of gyration of the cross-section controls the drop in TL at coincidence, called strength of coincidence. (C) 1997 Acoustical Society of America. [S0001-4966(97)05609-9] PACS numbers: 43.40.Rj, 43.40.Dx, 43.55.Rg [CBB].