Minimal Beamforming at Very Low Frequencies

Abstract

DLR tested a new system for the localization of sound sources in the infrasound range during measurements at the DLR research wind farm WiValdi. The measurement system consists of three pressure sensors that are mounted at the tips of an equilateral triangle with a side length of 12 m. The sensors are mounted according to the suggestions in DIN EN 61400-11 on round wooden plates with primary and secondary wind protection. Two such systems have been mounted on the ground with a distance of 100 m between them and about 120 and 400 m to the two wind turbines. Measurements have been performed under different conditions, with either one or both of the wind turbines running, with loudspeaker signals of tones at 20, 16, and 12,5 Hz, and with a commercial vibrator as it used on construction sites. Short data segments with a duration of one minute have been recorded and analyzed using the beamforming methods from the Acoular package of TU-Berlin. The results show that this relatively simple system can determine the direction of low-frequency sources, provided that the signal-to-noise ratio is sufficiently high.