Sibilant fricative sound production depends on the geometric and flow properties of the production system. Nevertheless, few studies deal with the potential impact of flow properties other than the inlet volume flow rate on the noise produced. In this work, an experimental study is presented using a replica based on a reconstructed oral cavity for the phoneme /s/. Initial flow conditions upstream from the sibilant groove are altered by varying the method of air supply. Statistical moments of the initial velocity distribution are characterized using hot-film anemometry and related to spectral features of the radiated acoustic pressure. Discrepancies in the dynamic amplitude (≤25%) and negative spectral slope (≤35%) observed at a constant Reynolds number but different initial upstream flow conditions are of the same order of magnitude as those previously reported in humans. This suggests that consideration of the upstream flow conditions is important in the study of sibilant fricative sound production.