Measures of vibrational localization on point-driven flat-panel loudspeakers

Abstract

Previous publications on flat-panel, or distributed-mode, loudspeakers generally assume that a localized driving force is able to spread energy evenly across the surface of a panel. However, investigations have shown that panel vibrations remain localized around the driving point at high frequencies, and this paper presents a deeper investigation into this phenomenon. Energy spreading will only occur when the panel is actuated in a frequency region with a low density of modes, as many modes actuated together will combine to form a band-limited delta function at the location of the driving force. A quantitative measure of localization is introduced, based on the ratio of the energy contained in a small region around the driving point to the energy contained in the entire panel. Simulations demonstrate that the frequency cutoff for localized vibrational behavior is dependent on the damping rate of the modes and the location of the driver. Experiments validate this theory by analyzing the vibrational behavior of a plate subject to small inertial drivers at various locations with a laser vibrometer.