The theory presented in two previous papers [Part I, J. Acoust. Soc. Am.72, 1056–1061 (1982) and Part II, J. Acoust. Soc. Am.74, 1013–1020 (1983)] is further developed and generalized to the case of no axisymmetry. Emphasis is given to a study of the parametric generated sound. Asymptotic formulas are presented, showing the development of the difference frequency sound from the source (transducer) into the farfield. New numerical results for the axisymmetric case are given for the linear and the parametric field of a source which is not radiating uniformly. New experimental results are reported and compared with the theory.