The mechanics by which sound evolves from unsteady boundaries and flow can be represented in acoustic analogies which provide a formal structure for analyzing the process of sound creation. The acoustic analogy of Lighthill has been the firmest foundation for modeling the jet noise problem. Studies of that problem have gradually increased in sophistication and scope to a point where the analogy itself has been developed to display characteristics that are novel and a little startling. The early models regarded turbulence as prescribed and concentrated purely on the acoustical consequences of that turbulence. But the more advanced analogies recognize definite constraints on acoustically important elements of turbulence and point to the susceptibility of the noise generating elements of turbulence to external stimulus. Other long waves induced by turbulence can be similarly analyzed and correspondingly interesting deductions made on vibrational fields induced by turbulent flow. This paper will describe some of the developments leading to notions that turbulence can be influenced by well-chosen external stimuli and speculate a little on areas where these effects might have significant practical applications.

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