This study investigates the phonetic realisations of voicing contrast in alveolar and postalveolar fricatives production in different word positions in order to understand the temporal and spatial production strategies used in the control of voicing and frication, and to provide a frame of reference for speech therapy despite the inter-speaker variation. Seven native speakers of German, originally coming from various regions, participated in the experiment. Acoustic signals were recorded onto DAT, and tongue palate contact patterns were recorded by means of electropalatography (EPG). The temporal parameters were measured using the acoustic signals and the spatial parameters were measured based on the EPG data. The corpus included real words with /s, z, S, Z/ occurring at word initial, medial and final positions. Temporal results showed that differences in the overall frication duration for voicing contrast occur at almost all positions (with longer duration for voiceless phonemes). However, voicing during the frication interval was a less reliable discriminator, particularly for Southern German speakers and at word final position. We found a positive correlation between the relative voicing duration and the amount of tongue palate contact for subjects who produced voicing. Especially for the postalveolars, voicing also coincides with more front articulation. Results are discussed with respect to laryngeal-oral co-ordination and aerodynamics.