I am in the process of writing a report on the Physics of Jet engines and I have come accross a problem I cannot comprehend. In the exhaust of many jet engines they allow the atmospheric air to mix with the air from the engine to reduce exhaust noise. From what I understand this allows the gasses to mix faster, but why does this help reduce noise? So far I think it is to do with the increased speed of mixing means that the pressure wave built up if of a higher frequency and so perhaps it is outside our hearing range? This doesn't seem quite right. If anyone knows of how it actually works, or any other mechanisms that are employed to reduce noise please tell me.