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External covers of machines, which are generally constructed from plates and shells, are used to reduce structureborne sound radiated by machines such as generators, gas turbines and compressors, etc. But these external covers also radiate airborne sound when excited by structureborne sound. In addition, depending on the insertion loss of these plate enclosures, a part of the airborne sound from the machines enclosed by them is transmitted across to the external surrounding. By providing local stiffeners on these covers can improve their insertion loss and reduce their sound radiating capability to some extent. But that is not sufficient. Hence, in the present work, the flat nature of plates is changed by attaching triangular stiffeners, and thus introducing discontinuities, to obtain various corrugated configurations. Several test samples were fabricated by providing various geometric configurations of corrugations on flat plates for exploring the possibility of increasing sound insertion loss. This was verified through experiments performed in an anechoic room using a source airborne sound. Initially, sound insertion loss was measured for a set of corrugated plates comprising of triangular prismatic cavities, formed between the flat surface of plates and inverted 'V' shaped stiffeners. Similar experiments were performed for another set of corrugated plates in which acoustic cavities were avoided, and sound insulation performance of both the set of corrugated plates was compared. The size of the plates for the experiments was kept small within manageable limits for conducting experiments. Significant improvement in the sound insertion loss was observed for both sets of corrugated plates, as compared to a flat bare plate of the same size.
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