Quantal theory aims to elegantly describe (using physics) and organize all the acoustic features of all possible sounds into a matrix. (See chapter five in Acoustics Phonetics) The ultimate constraint on all speech sounds is the physical articulatory system itself, thus supporting the claim that there can only be a finite set of sounds among languages. The reason that the set of speech sounds is finite is that while the movement of the articulators is continuous, only certain configurations tend to be articulatorily and/or acoustically stable, giving rise to fix frequencies for formants that form sounds that are relatively universal for all languages (i.e. vowels and consonants). Each acoustic sound can thus be described by a handful of defining features (usually binary). For example, lip-round (either on or off) is a feature. Tongue height (either high or low) is another feature. In addition to these defining features which serve as the essential description of the acoustic sounds, there are also enhancing features which help to make the sounds more recognizable. For each of these features, one can apply Stevens' methodology to first use a tube model to model the articulators, and predict the resonant frequencies, then collect data to examine the acoustic properties of that feature, and finally to reconcile with the theoretical model and summarize the acoustic properties of that feature.
