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Experimental Investigation of Sound Reduction by Thin Air Layers [Poster]

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  • Musicology
  • Physics


Experimental investigation of sound reduction by thin air layers T.G.H. Basten, W.M. Beltman, H. Tijdeman University of Twente Twente Institute of Mechanics P.O. Box 217, 7500 AE Enschede, The Netherlands phone +31-(0)53-4895618/2460, email [email protected] Introduction A thin air layer between two flexible plates can dissi- pate a significant amount of vibrational energy by its viscous and thermal behaviour. Reducing low frequent sound Low frequent sound is usually re- duced by introducing large amounts of mass in a structure. The objective of this research is to investigate if the viscothermal effects in thin air layers can be used to reduce low frequent sound. Applications are for instance motor shielding or silent walls. Figure 1 : Sound reduction by a thin air layer Tools Tools with which the viscothermal wave propagation in relation with fluid-structure interaction can be studied have been developed. Finite elements Acoustic elements which take into account viscous and thermal effects and which enable full fluid-structure interaction are implemented in the B2000 Finite Element Program. Experimental setup With a special experimental setup the influence of the airgap on the dynamical be- haviour of a double wall panel has been investigated. Figure 2 : Experimental setup Experimental Method The method is based on the energy balance. The en- ergy which is dissipated in the airgap (Wdis) is calcu- lated from the energy fed to panel 1 via the shaker (Win) and the radiated acoustic energy (Wrad): Wdis =Win�Wrad The radiated energy Wrad is measured with a sound intensity meter: Figure 3 : Intensity measurements on double walls The calculated and measured Energy Loss Wdis=Win show the effectiveness of thin air layer(s): Figure 4 : Experimental and numerical results Conclusions and further research The dissipative behaviour of a viscothermal air gap has been demonstrated both experimentally as nu- merically. The step to practical applications will be made. R

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