Abstract:
The increase in polulation 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.Transmission ththrough walls and ceilings in the lower frequency region of human hearing is particularly important, but is a difficult problem. Can we design an acoustic insulation system that provides improved sound insulation performance over a conventionl system within this frequency range? This paper outloines an investigationinto novel meta-materials known as Locally Resonant Structures. These structures can exhibit acoustic band gaps, or frequency ranges of unusually low soiund transmission.One dimensional mathematical models are used in conjubction with finate element analysis toto develop various locally resonant element concepts functional below 1kHz.Acoustic testing is then used to experimentally verify the performance of the elementsthrough comparisons with modelling data.Various resonator elements have shown a peak effective mass up to fifty times greater than their rest mass. Such structures have increased peak transmission losses by as much as 40dB over 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 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.