ON STRUCTURE-BORNE SOUND - EXPERIMENTS SHOWING THE INITIAL TRANSIENT ACOUSTIC-WAVE FIELD GENERATED BY AN IMPACTED PLATE

The initial propagating transient acoustic field in air generated by a n impacted plate is visualized. The transient traveling flexural waves in the plate created by the impact are shown, simultaneously. The exp eriments are performed using double pulsed holographic interferometry. It is shown that flexural waves in a plate act as a series of traveli ng acoustic sources. Since the flexural waves in the plate are dispers ive the trace matched acoustical waves further away from the impact so urce propagate at a smaller angle relative to the plate than those clo ser to the impact. An observer situated close to the plate and away fr om the impact point will first receive high-frequency components of th e sound. A quantitative evaluation of the acoustic field also shows th at if there is a transient increase in pressure on one side of the pla te there will be a similar decrease on the other side.