The development of mixing engines (such as bypass and turbofan engines) has opened a new area to be explored for possible means of reducing jet noise. Analytical studies and experimental developments were made so that the noise characteristics of various mixing engines could be identified in terms of engine‐design parameters. The method of the program was based on an analysis of engine‐flow parameters, such as fan‐pressure ratio and bypass ratio, in terms of energy distribution in the primary and secondary jet streams. The results revealed that (1) in geometrically different exhaust‐nozzle configurations (ranging from short duct through coplanar to fully mixed), jet noise decreases as the mixing of 2 flows becomes more complete; and (2) appropriate combinations of engine variables (such as high bypass ratio with high fan‐input energy) will lead to a significant reduction in the jet noise from bypass engines. The results of this program will provide the menus of establishing acoustically optimum design criteria for bypass engines.