A discussion on the origin and treatment of noise in industrial environments - Reduction of noise by the use of damping materials

Abstract

Vibration damping materials are used to damp out the bending vibrations of sheet-metal structures. In this way, weakly damped natural and resonant vibrations of the sheet-metal which lead to radiation of disturbing noise into the adjacent air are suppressed, the noise level being thus reduced. Free bending and strain waves can transport sound energy via extended sheet-metal structures to points far away from the sources, causing sound radiation into the air. In this case too, the application of vibration damping materials will be beneficial because in this way the structure-borne sound propagation will be partially suppressed by the attenuation of the free-bending waves. Furthermore, the damping of the bending vibrations can essentially improve the sound insulation of light-weight structures, so-called sandwich walls, consisting of outer metal plates and an air cushion between, filled with sound-absorbing material. The damping of the metal plates diminishes the influence of resonances and coincidences which otherwise would lead to a diminution of the sound reduction of the sandwich wall (Stiiber 1956, 1965). Finally, it has been shown that the fatigue life of metal panels, for example near the outer walls of jets which are excited to flexural vibrations by the random pressure of the air-borne sound field of high intensity, is increased as a result of the damping of the panels (Kurtze & Westphal 1965).