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The sound power level is the most important quantity that characterizes the noise emission of machinery. Following standardized procedures, it is usually calculated from sound pressure levels measured at a number of reference positions on a surface enveloping the object. The resulting value does not hold any direct information on the noise contributions of subcomponents. However, effective noise reduction necessitates a prior identification of acoustic sources and their characteristics. Combining the enveloping-surface method with microphone array measurements facilitates the evaluation of synchronously noise-emitting subcomponents. The application of this technique on a water pump with a four-stroke engine as power source is presented in this paper. The microphones are arranged on a cuboid surface surrounding the setup. The measured data is processed so as to yield sound power levels in a defined 3D focus region.