Beamforming Techniques for Environmental Noise

Abstract

A problem of practical interest when dealing with outdoor acoustic measurements is to estimate the noise contributions from di erent directions around the measurement point. This estimation can be done by means of microphone arrays. More speci - cally, circular arrays are suitable for this purpose as, in combination with proper signal processing techniques, they are capable of mapping the sound eld in a plane over 360 . Two processing techniques meant to be used with circular arrays are implemented: the `classical' Delay-and-Sum beamforming and a novel technique called Circular Harmonics beamforming. The latter is based on the decomposition of the sound eld in series of circular harmonics. The performance of these beamforming techniques is analyzed by means of simulations and evaluated by two parameters, the resolution and the maximum side lobe level. Making use of the results of the simulations, a circular array has been designed for the localization of environmental noise sources around a measurement point. Finally, a prototype implemented in accordance with the design has been tested in anechoic conditions. The results, which agree very well with the simulations, reveal that the array is suitable for the purpose of concern.