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Active Control of Sound Transmission through a Double Wall Structure


O. Kaiser

vol. Diss. ETH Nr. 14109

One way to tackle the control of stochastic noise in three dimensions is to reduce the sound transmission to t he zone of interest. In buildings, windows are often the weak link in protecting the interior from outside noi se. In particular, double glazed windows have a poor sound insulation at low frequency around the mass-air-mas s resonance (double wall resonance). Since the passive means for windows are exhausted, an active controller t hat increases the transmission loss in the low frequency range is an attractive approach to reduce the noise l evel in buildings.
Previously suggested feedforward controllers need reference microphones to measure the disturbance outside and error microphones for the adaptation somewhere in the room. For a real window this is unpractical or even inf easible. These limitations can be overcome with the feedback controller presented here, that only uses sensors and actuators in the cavity of the double glazed window.
For the modeling, the system is decomposed into five subsystems that are governed by coupled partial different ial equations. These equations are solved using modal expansion. Because the coupling between the subsystems c an be calculated as well, it is possible to assemble the subsystems into one single state space model.
The eigenfrequencies and mode shapes predicted by the model are validated using a laser vibrometer. In additio n, transfer functions measured on the structure are compared to those calculated from the model. In both cases , the measurement and the prediction agree very well. From the validated model, design guidelines are derived. For example, it is shown that there are some uncontro llable modes if the double glazed window is symmetrical. It is confirmed experimentally that the performance o f an active controller is doubled if symmetry in the construction of the double wall panel is avoided. The mod el is also used to optimize the sensor and actuator locations. Four different controllers - two feedforward and two feedback strategies - are designed, implemented and compared. With feedback the noise transmission around the mass-air-mass resonance can be reduced by 13dB, compared to 18dB with a feedforward controller.

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Type of Publication:

(03)Ph.D. Thesis

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% Autogenerated BibTeX entry
@PhDThesis { Xxx:2001:IFA_316,
    author={O. Kaiser},
    title={{Active Control of Sound Transmission through a Double Wall
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