With the goal of improving human-robot speech communication, the localization of multiple sound sources in the 3D-space based on the MUSIC algorithm was implemented and evaluated in a humanoid robot embedded in real noisy environments. The effects of several parameters related to the MUSIC algorithm on sound source localization and real-time performances were evaluated, for recordings in different environments. Real-time processing could be achieved by reducing the frame size to 4 ms, without degrading the sound localization performance. A method was also proposed for determination of the number of sources, which is an important parameter that influences the performance of the MUSIC algorithm. The proposed method achieved localization accuracies and insertion rates comparable with the case where the ideal number of sources is given.