A modal approach to lightweight partitions with internal resonators

Theoretical models of sound transmission through partitions are well known as far as homogeneous materials are concerned. However, in reality only a small fraction of materials are literally homogenous. In recent years, considerable interest has been taken in theoretical models of inhomogeneous structurcs. First results have revealed the opportunity to modify the sound transmission loss at selected frequencies due to inhomogeneous material properties. Using the concepts of forced inhomogencities, increasing efforts have been made into the development of new materials or structures with higher sound transmission loss at certain frequencies. This paper presents the implementation of local resonance systems into lightweight partitions in order to improve the sound insulation of lightweight structures at lower frequencies. The benefits of double-panel partitions are combined with the frequency dependent effect of distributed vibration neutralizers. The main focus is placed on the location and number of vibration neutralizers. Based on the modal expansion method a beam model has been derived taking the modal behaviour of both panels into account. The radiated power has been calculated using modal radiation efficiencies. The effects of the vibration neutralizers have been quantified in terms of the resulting sound transmission loss. Results are presented of parameter studies that demonstrate the behaviour of lightweight structures dependent on the properties, the distribution and number of the internal vibration neutralizers