An Acoustic Variable Specifying Time-to-Contact

Abstract

The acoustic intensity structure generated by the rectilinear convergence of a compact sound source and a point of observation is analyzed. It is shown that an acoustic variable specifying the time-to-contact with the source is available at the point of observation, given certain assumptions about the source, the distance between the source and observation point, and the environment. This variable is T = 2I/(dI/dt), where I is the time-averaged intensity. Possible extensions of the analysis are discussed.