Over the last twenty years, 3-D audio technologies have advanced significantly despite the difficulties in implementing them. However, their performance in providing information, especially about the distance of a sound source, remains imperfect. Therefore, more researches on distance cues are indispensable to achieve more effective technology. In this paper, we try to show how the conventional cues change as the distance of a sound source varies, by means of measured impulse responses using the swept-sine method and modeled impulse responses using CATT Acoustics. It is well known that the conventional cues comprise loudness, spectral information, reverberation and binaural information. Among these, we focus on the reverberation cue to describe the distance of a sound source. Some researches have shown that reverberation can give listeners absolute distance information, but the implementation using this cue is unfeasible because there are no well-defined parameters. In this paper, we also try to validate reverberation as a feasible distance cue by suggesting early decay time (EDT) and clarity index, C80, as the parameters for controlling the perceived distance with the reverberation cue.