A common problem in the field of speech synthesis is the lack of a quantitative description of speech sounds applicable to both vowels and consonants. Usually only vowels are specified in terms of formant frequencies. This paper proposes a parametric description of the steady-state zones of all non-plosive phones based on centroids in the log area ratio parameter space. For each phone, a centroid is computed as the center of gravity over an ensemble of realizations produced by a single speaker in different contextual situations. The centroids are quantitatively compared to one another by means of an objective distance measure. In addition some information relating to the dynamic behaviour of the speech signal is obtained by signal destruction and construction experiments. All these data then serve to discuss several phonoacoustic problems encountered in the delimitation of the German phones, with respect to vowel quality and quantity, for example.