Woo, J., Kim, D., and Ih, J., "Virtual Formation of a Woofer at the Roof Panel of a Vehicle by Using Array Actuators," SAE Int. J. Passeng. Cars - Mech. Syst. 9(3):1086-1090, 2016, doi:10.4271/2016-01-1825.
To hear the powerful and spectrally rich sound in a car is costly, because the usual car audio system adopts small loudspeakers. Also, the available positions of the loudspeakers are limited, that may cause the reactive effect from the backing cavity and the sound distortion. In this work, a part of the roof panel of a passenger car is controlled by array actuators to convert the specified large area to be a woofer. An analogous concept of the acoustic holography is employed to be projected as the basic concept of an inverse rendering for achieving a desired vibration field. The vibration of the radiating zone is controlled to be in a uniform phase, and the other parts outside it are to be made a no-change zone in vibration. The latter becomes a baffle for the woofer, and the backing cavity is virtually infinite if the sound radiation into the passenger cabin is only of concern. Small array actuators are located in the periphery of the target roof panel avoiding the stiffener members. The rendered zonal activities in vibration are fulfilled by solving an inverse vibro-acoustic problem employing the bending wave control. The inverse technique determines the proper weighting for each actuator in the array. Experiment is conducted on a cutout roof panel of a midsize car. The preliminary test result shows that the localized in-phase vibration control yields a maximum deviation of 3˚ in phase differences at the speaker zone.