Conventional pipe laggin-es irrcorporate a porous iacket and an impervious outer cladding sheet. It has been observed during investi-sations of such pipe Iaggings that a simple porous jacket applied b1' itselfto a pipe can actually increase the sound radiated. Reasons for this phenomenon are discussed. The effect of a rigid frame porous jacket around a pipe is examined theoreticall-t' for the breathing. bending. and ovalling modes of pipe vibration. The predicted insertion loss associated with

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... he bending n.rode of pipe libration is compared with the conesponding experimental result and some of the results of a parametric stud1, are given. O