Sound insertion loss of stiffened enclosure plates using the finite element method and the classical approach

This paper reports a theoretical and experimental study of insertion loss of stiffened enclosure plates which are used for noise control in industrial machines, automobiles, trains and aircrafts. The theoretical analysis is based on the finite element method in [1] for the structural part, and the classical solution suggested in [2, 3] for the acoustic part. The effects of boundary conditions, acoustic resonance and structural resonance on the insertion loss are studied. The theoretical results agree reasonably well with the experimental results. Both numerical and experimental results point to two important findings: 1) the coupling effect between the (1, 0) acoustical mode and the (2, 1) structural mode is an important factor which can cause deterioration of the insertion loss of an enclosure plate; and 2) stiffeners can be used to enhance the insertion loss ability of an enclosure plate at the frequencies below the fundamental resonance. However, at other frequencies, the enclosure plate could give worse insertion loss performance. (C) 1998 Academic Press.