Abstract
One of the authors has developed a technique to visualize the transient vibration on unstable structure, for example, paper, film and so on, by using sound pressure measurement at near field. In this paper, the theory is tried to be constructed in order to verify the technique. The sound pressure radiated from free bending wave on infinite beam and the knowledge on "very near filed" are summarized. The technique is discussed by using an aluminum bar which vibration responses can be directly measured by accelerometers and laser vibrometer on the bar and which sound pressure is measured by microphones near the bar. As a result, it is demonstrated that the transient behaviors of an OHP film which is unstable structure can be recognized by the technique.
