A common feature of public speech in Catalan is the placement of prominence on lexically unstressed syllables ("emphatic stress"). This paper presents an acoustic study of radio speech data. Instances of emphatic stress were perceptually identified. Within-word comparison between vowels with emphatic stress and vowels with primary lexical stress reveals that the former are characterized by having a high tone, higher F0 scaling, and greater intensity, but shorter duration with respect to lexically stressed vowels. Emphatic stress can thus be characterized as anchoring an intonational pitch accent on a lexically unstressed syllable. When this phenomenon occurs, primary lexical stress is still cued by duration. Compared with other lexically unstressed vowels, vowels with emphatic stress have greater duration and intensity, and less vowel centralization. Thus, vowels are hyperarticulated when bearing emphatic stress. In particular, schwa is more open, without merging with /a/. Regarding the distribution of emphatic stresses, the most common pattern observed is binary or rhythmic ("les institucions" "the institutions"), with emphatic stress occurring two syllables before the primary stress. Less frequently, emphatic stress appears on the first syllable of the prosodic word ("nacionalitats" "nationalities"), occasionally producing stress clash ("el marc" "the framework"). (Contains 9 notes, 10 tables and 13 figures.)