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Active Sound Power Absorbers: Their Effect on Sound Transmission through Wall Openings.

by Emms, Grant William

Abstract (Summary)
Restricted Item. Print thesis available in the University of Auckland Library or available through Inter-Library Loan. This thesis proposes the use of active sound absorbers to create an acoustic barrier in an aperture in an otherwise acoustically opaque wall. An active sound absorber is an active noise control method with the aim being the absorption of sound power. The aim of this present work is to determine whether active sound power absorbers can be useful in the reduction of the transmission of sound through apertures. Monopole, dipole, and conjoint monopole and dipole absorbers were examined. Initially, a mathematical model of an opening in a wall was constructed, using a coupled boundary element method. This was used to test the effectiveness of various theoretical active sound power absorbers. The results of these tests showed that a combination monopole-dipole absorber was able to substantially reduce the sound power transmission through the opening, for wavelengths larger than the dimension of the opening. It was observed that increasing the number of monopole-dipole absorbers evenly over the opening extended the effective performance to smaller wavelengths. An active sound power absorber was constructed from two long-throw electromagnetic sound drivers to show that an active sound absorber could be realised in practice. The experimental active sound power absorber was placed in an opening in a wall to observe the effect the absorber had on the sound transmitted through the opening. It was found that very accurate knowledge of the phase response of the absorber sensors was required for effective low frequency absorption. A suitable control method for an active sound absorber was also investigated. Adaptive algorithms based on the LMS method were investigated and adapted to the requirements of active sound power absorption.
Bibliographical Information:

Advisor:

School:The University of Auckland / Te Whare Wananga o Tamaki Makaurau

School Location:New Zealand

Source Type:Master's Thesis

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ISBN:

Date of Publication:01/01/2000

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