Application of a tuned vibration absorber for increasing the sound transmission loss of acoustic panels at low frequencies

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Copyright: Ruber, Karel
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Abstract
Structural partitions provide good sound insulation in medium and high frequency ranges. However at low frequencies partitions often do not provide adequate noise insulation and other methods of increasing the sound insulation in those frequency ranges are required. Acoustic partitions transmit noise by vibrating as a result of sound waves impinging on them; therefore reducing the magnitude of the partition vibration will be beneficial for increasing their noise insulation performance. Tuned Vibration Absorbers (TVAs) have been successfully used for over a hundred years to reduce structural vibration in various industries and in a large number of applications. Applications of TVA for reducing sound transmission through panels are relatively new and most researches focused on tuning the TVA to the excitation frequency. The effect of adding a Tuned Vibration Absorber, which is tuned to the frequency of the lowest minima of the Sound Transmission Loss (STL) curve- the first panel resonance, is investigated in this thesis. Acoustic insulation panels are often part of small sealed enclosures such as electronic equipment cabinets. The effect of the air sealed in an enclosure backing a panel, is to increase the stiffness of the panel artificially raising the first natural frequency of the panel. This research confirmed the effect of the air cavity added stiffness and the frequency increase of its first vibration mode, however the effect on the STL in this frequency region was found to be is insignificant. The analytical and FEA results were confirmed with tests. An optimisation study for maximising the STL of a panel with an attached TVA was performed. The optimal stiffness and damping for a given dynamic mass of TVA and panel was calculated using lumped elements for the panel and the TVA. The predicted performance was also calculated with FEA of a panel with a lumped parameter TVA attached. Alternative methods of implementing the required stiffness and damping were investigated. Linear flexures in the form of pairs of flat disk springs can provide an essential uniaxial movement and the dimensions of a pair of disk springs were determined to provide optimal stiffness. Eddy currents can provide viscous like damping without contact or the need of seals between the moving parts. The required optimal damping was obtained with a configuration of three axially aligned magnets and ferromagnetic spacers.
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Author(s)
Ruber, Karel
Supervisor(s)
Kanapathipillai, Sangarapillai
Randall, Bob
Feng, Ningsheng
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Publication Year
2018
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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