A microphone array that emphasizes sound sources located in a particular 2-dimensional area is described. We previously developed a method that estimates the power spectra of target and noise sounds using multiple fixed beamformings. However, that method requires the areas where the noise sources are located to be restricted. We describe the principle of this limitation then propose a procedure that investigates the possibility of the existence of a sound source in a target area and other areas beforehand to reduce the number of unknown power spectra to be estimated.