Optimum near-field performance of microphone arrays subject to a far-field beampattern constraint

This article addresses the problem of maximizing the near-field gain of a microphone array subject to a constraint on the far-field beampattern. The problem arises when acquiring speech from a near-field talker in the presence of a strong source of interference located farther from the array. When the angles of incidence from the near-field target and the far-field interference are identical, enforcing a null constraint in the interference direction reduces array gain and robustness, This article shows how to mitigate this effect by selection of the constrained response level. A suitable selection is to force the beampattern in the interference direction to be proportional to the unconstrained beampattern. The proportionality constant can then be used to trade off interference reduction and array gain. Specific numerical examples are provided. (C) 2000 Acoustical Society of America. [S0001-4966(00)03711-1].