Space

Acoustic near field sound source localization

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Arrays of PU probes measuring both sound pressure and acoustic particle velocity offer a unique opportunity for acoustic near field measurements that are “reverberant room proof”.

With microphones only, there is no appropriate method to apply acoustic near field based sound source localization techniques on space structures tested in reverberant rooms that are characterized by a high level of diffusiveness. A single layer array of sound pressure transducers is used in the classical near field holography method and placed at a certain distance from the surface of the test object in order to reconstruct both the sound pressure and the particle velocity at the test surface.

As these planar microphone arrays cannot distinguish between the sound coming from the source and the sound coming from the background, reflections and ambient noise in general make the results unusable.Obviously, these conditions are not met in reverberant rooms designed for space structure testing.

Two layers of sound pressure transducers are used for so called conformal mapping.The phase and amplitude differences between the pressure signals measured at the two layers are used to estimate which part of the sound comes from the source.However, small errors in the phase of the pressure microphones can make this estimation inaccurate.

In a sound field which is almost diffuse (as it is meant to be the case in reverberant rooms), sound intensity simply cannot be determined using spaced pressure microphones.

Only the use of an array of PU probes as such already allows the direct measurement of both relevant quantities at the surface of the testing object.

However, especially for the space industry, there is a need to analyze the test object in the smallest possible detail.As the channel count of the array is usually limited for both costs and practical reasons, on top of the direct measurements, additional signal processing techniques can to be applied for the interpolation of data, increasing the “virtual channel count”.