This paper explores the contribution of voice source modulation to the perception of prominence, following on previous analyses of accentuation, focus and deaccentuation. A listening test was carried out on a sentence of Irish with three accented, prominent syllables (P1, P2, P3). Using inverse filtering and resynthesis, a 'flattened' version was generated, with only slight declination of f(0) and other voice source parameters. The global waveshape parameter R-d was modulated to provide (i) source boosting (tenser phonation) on either P1 or P2, and/or (ii) source attenuation (taxer phonation) following (Post-attenuation) or preceding (Pre-attenuation) P1 or P2. R-d variation was achieved in two different ways to generate two series of stimuli. f(0) was not varied in either series. Twenty-nine listeners rated the prominence level of all syllables in the utterance. Results show that the phrasal position (P1 vs. P2) makes a large difference to prominence judgements. P1 emerged as overall more prominent and more readily 'enhanced' by the source modifications. Post-attenuation was particularly important for P1, with effects equal to or greater than local P-boosting. In the case of P2, Pre-attenuation was much more important than Post attenuation.