Alternative approaches to the modelling of the multiple pure tones

Several theories have sprung up which attempt to explain the phenomenon of the multiple pure tones. These explanations could be classified as gasdynamic and acoustic theories. The acoustic theories themselves fall into two categories: one taking into account the higher order modes and another restricted to plane waves only. Of the higher order mode theories, some are based on a finite degree of resonance and the alternative due to the author and his colleague is based on an infinite degree of resonance. It turns out that only the gasdynamic theory and the infinite degree of resonance theory explain the phenomenon as it is generally encountered. It has been shown that these two theories are essentially isomorphic. However, convention has limited both the theories in their scope. The resonance theory can explain, with advantage, effects of absorbents and suggest new techniques of suppression. The gasdynamic theory is probably better suited for source-modification studies. Together, they represent a deeper understanding of the underlying phenomena.