When there are multiple noise sources in the same frequency bands, it is important to know their spatial contributions to their ultimate radiation at the point of interest or the region. This problem requires decomposing partial fields, which are the sound fields of individual sources. Near-field acoustic holography (NAH), which visualizes the summation of partial fields, has extended to effectively decompose the partial fields. This paper introduces its basic idea and theory. Typical examples are also introduced. First example is a six-speaker experiment, where the speakers were operated independently. Second example is a vortex shedding experiment, where compressed air was injected to a circular cylinder. Therefore vortex was generated at the downstream. Third example is an engine experiment, where some frequency components had multiple noise sources. Forth example is a wind noise experiment of an automobile at a high speed, which was performed in Hyundai aeroacoustic wind tunnel.
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