In this paper, we describe a robotic spatial sound localization system using an auditory interface with four microphones arranged on the surface of a spherical robot head. The time difference and intensity difference from a sound source to different microphones are analyzed by measuring the HRTFs around the spherical head in an anechoic chamber. It was found while the time difference can be approximated by a simple equation, the intensity difference is more complicated for different azimuth, elevation and frequency. A time difference based sound localization method was proposed and was tested by experiments. A sound interface for human listeners is also constructed by four loudspeakers with similar arrangement as the microphone set. This interface can be used as 3-D sound human interface by passing the four channel audio signals from the microphone set directly to the four loudspeakers. It can also be used to create 3-D sound with arbitrary spatial position which is determined by a virtual sound image or by the sound localization system.