In this paper we investigate the spectral properties of vowels in a Northern Australian language, Kunwinjku. The language illustrates typical vowel dispersion patterns of other languages of the region, and of 5-vowel languages in general. The spectral properties of vowels suggest a system of sufficient dispersion, with phonemic close vowels being realized in the close/mid-close region of the vowel space and with a general anchoring of the system by an open central vowel. Vowel height also interacts with vowel segment duration, with open vowels being generally longer than relatively close vowels.