Vibration and sound radiation of a plate

Abstract

Because of their many vibratory resonances, plates are mechanically soft and their suspending structures have considerable effect on their vibration and sound radiation. Experimental evaluation of acoustic properties of plates is therefore difficult. Plates of different shapes and dimensions were supported in such a way as to eliminate the effects of the supports on the vibrations and the velocity amplitudes due to point forces were recorded by phonograph cartridges and microphones in the near sound field. The results show that the many vibratory modes generate “hotspots” on the plates. The attachment of ribs and supports disturbs the vibration field and leads to localized areas of increased sound radiation. Long wavelength acoustic holography was used to locate on the vibrating plates the sources of farfield sound. These regions were also investigated by recording the vibratory and nodal line patterns of the plates by a nearfield microphone method. This combination of techniques has a unique capability to locate acoustic sources on vibrating structure. [Work supported by NASA and ONR.]