Detection of acoustic sources using long-wavelength acoustical holography

Sound sources from vibrating circular and ribbed rectangular plates are detected by holographic means using a microphone scanner and associated photographic equipment. Reconstruction of the wavefront from the acquired acoustical holograms reveals the areas on the plates which generate the far-field acoustic radiation. In all cases, the plates were driven below their coincidence frequency. The location of the sound sources on the plates supports the theory of acoustic radiation from complex vibrators except for irregularities which are due to inhomogeneities of the plate material, nonlinearities of the holographic technique, and the speckle effect.