Measurements of sound pressure in a very near field

Numerical calculations of sound pressure field from a known vibration velocity field are often used for the prediction of the acoustic behavior of the complex noise sources. In some cases an inverse procedure is possible. A calculation of velocity field on the vibrating surface can be performed based on measured sound pressure field. It is demonstrated, that inverse calculation is possible if the sound pressure field is measured in the near field, and that there is practically no need for the inverse calculation if measurements are performed in the very near field.