loudspeaker radiation pattern Display of the radiation pattern of a loudspeaker The Acoustic Holography is an altenrative to the beam forming method. This method is able to handle nearfield and farfield components. The nearfield components decay exponentially. Therefore the distance to the source has to be as small as possible. Using a regular grid in two dimensions the Fourier transfromation about time and the two directions in space is used. The knowledge of the wavelength in two dimensions, of the frequency and the wave speed in air allows the derivation of the wavelength and -type in the third dimension. The wavelength in the third dimension is used to project the coherent sound field from the grid plane into a plane infront of the grid as close as possible to the surface of the structure.

The Acoustic Holography is an altenrative to the beam forming method. This method is able to handle nearfield and farfield components. The nearfield components decay exponentially. Therefore the distance to the source has to be as small as possible. Using a regular grid in two dimensions the Fourier transfromation about time and the two directions in space is used. The knowledge of the wavelength in two dimensions, of the frequency and the wave speed in air allows the derivation of the wavelength and -type in the third dimension. The wavelength in the third dimension is used to project the coherent sound field from the grid plane into a plane infront of the grid as close as possible to the surface of the structure.

     

Display of the radiation pattern of a loudspeaker

The method so far can be applied to coherent sound fields. An extension to incoherent sound fileds is possible using the spatial transformation of sound fields (STSF). The principal component analyis (PCA) of all measurement channels is used to speperate the coherent components. The Acoustic Holography is applied to every component separately.