Modelling and Experimental Validation of Complex Locally Resonant Structures

Andrew Hall , Emilio Calius , George Dodd , Eric Wester

New Zealand Acoustics, 24(2), pp.12- 23 . (2011).

The increase in population worldwide has highlighted the inadequacies of sound insulation in buildings. The problem is particularly evident in medium-high density housing situations, which are projected to become 30% of Auckland’s housing by 2050. This will have implications on occupants’ health, productivity and quality of life. Prevention of sound transmission through walls and ceilings in the lower frequency range of human hearing is particularly important, but is a difficult problem. This problem provides an opportunity to ask the question: Can we design an acoustic insulation system that provides improved sound insulation performance over a conventional system, within this frequency range? This paper outlines an investigation into novel meta-materials known as Locally Resonant Structures. These structures can exhibit acoustic band gaps, or frequency ranges of unusually low sound transmission. One-dimensional mathematical models are used in conjunction with finite element analysis FEA to develop various locally resonant element concepts functional below 1kHz. Acoustic testing is then used to experimentally verify the performance of the elements through comparisons with modelling data. Various resonator elements have shown a peak effective mass up to fifty times greater than their rest mass. Locally resonant structures have increased peak transmission losses by as much as 40dB over that of a non-resonant structure of equivalent area density within the designated frequency range. These resonators can be distributed throughout the wall structure on a scale shorter than the wavelength of structural vibrations in the wall matrix. The resulting system has the potential to provide significantly higher transmission loss at low frequencies than conventional wall systems of similar size and weight. The longer term goal is to determine an effective design of local resonator that can be incorporated into a practical insulation system