By use of the S. E. A. evaluation method by Crocker and Price, a considerable discrepancy between the theoretically evaluated values and experimentally observed values can be seen specially in the low frequency region. In this paper, a new trial of improved S. E. A. method is proposed which introduces the proper nonresonant power flow II_15 into the Crocker and Price's method. A good agreement between the theoretical values and experimental data is able to be found for several different types of double-walls. Essentially, our improved method is applicable not only to a general type of parallel double-wall but also to an absorbent double-wall having sound-absorbing material around the edges of the air cavity between two panels. Furthermore, for the purpose of confirming its effectiveness and flexibility, the evaluation method is newly proposed for non-parallel double-wall which has not been previously studied from a theoretical viewpoint. An agreement between theory and experiment is satisfactorily explained for these three kinds of double-wall structure by using our improved S. E. A. method.
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