Large-scale outdoor sound field control

The feasibility and the performance of controlling low frequency sound of loudspeaker systems under varying atmospheric conditions is examined experimentally. In the experiment, a control subwoofer array is canceling the sound of a primary subwoofer array over long distances (∼100 m) and in large areas (∼320 m²) using the pressure-matching method. To avoid the measurement of the sound field over the entire control area, a sound propagation model is introduced that is fitted in situ to model the radiation properties of the loudspeakers and the variation of the speed of sound. The results show that the control system reduces the sound pressure levels by up to 15-20 dB over the subwoofers' frequency range. However, the reduction can vary considerably depending on the specific atmospheric condition. The model-based approach reduces the number of required measurements and achieves similar reduction performance to the control based on direct measurements with considerably fewer microphone locations while also being more robust. Additionally, the sound propagation model enables the reduction of acoustic energy in virtual control zones that are far away from the microphone location. The investigated methodology has a direct application in the mitigation of sound from outdoor concerts.