A comparison of analytical models and experimental results for the acoustic response in a non-rigid-wall enclosure

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Virginia Tech


The work presented in this thesis was motivated by the need for an accurate modeling approach for the acoustic response in a non-rigid-wall enclosure. The acoustic response in any enclosure is determined by the boundary conditions at the interior surface of the enclosure walls, and the types of sources present. The analyses presented in this thesis assumed that the sources were either at the surface of the enclosure, or interior to the enclosure walls.

Three different analytical modeling approaches were investigated and presented in this thesis for the acoustic response in a rectangular enclosure. A reference model assumed that the walls of the enclosure were rigid, corresponding to an infinite acoustic impedance boundary condition. The acoustic pressure response was expressed in terms of the characteristic rigid wall acoustic modes of the enclosure. The second modeling approach used a finite acoustic impedance boundary condition to model the influence of non-rigid walls on the acoustic response. The third modeling approach treated the vibration of the enclosure walls as additional sources which were constructed from the in vacuo structural modes of the enclosure. The acoustic pressure was expressed in terms of the rigid-wall acoustic modes. High-dimensional state variable and transfer function models are presented, along with discussions of their validity and performance as model parameters vary. The frequency response functions generated using these three models were compared to the actual acoustic frequency response function obtained experimentally for a non-rigid-wall, plexiglass enclosure. It was found that the finite impedance model generated an acoustic response which best matched that of the actual acoustic response in magnitude and frequency; however, further development of this model is needed to account for structural resonances of the enclosure.



acoustic, enclosure, Modeling, impedance, Control