Beam forming of a 64 microphone array is applied when instationary or moving sound sources have to be processed. Numeric simulation corresponds with measurements of monopole sources in an anechoic room concerning dynamic relations and side lobe influence.
Example of S_TOOLS-STx spectrograms of the sound originating from an ICE, passing by at v = 300 km/h. Recorded with the 8 x 8 microphone array as shown above (distance 7.5m). Frequency range (ordinate) 0 - 14000 Hz, time axis: 5s.
The main aerodynamic sources of the pantographs can be seen on the uppermost spectrogram (1). The second spectrogram is focussed on the roof level of the train (2). The third spectrogram shows sound energy associated to the height of the wagon windows (3). On the bottom (4) the sound of wheel trail contact is dominant. Spectrograms show the time varying character at different frequencies as well as on arbitrary foci computed from the 64-channel microphone array signals.