Good news for anyone living near an airport: someone's just thought of a way to quiet down those noisy jet planes. Dimitri Papamoschou at the University of California filed a patent earlier this year for a jet-engine silencer. Recognizing that a great deal of the noise jets create is due to turbulence in fast-flowing air from the engine, he clever devised a way to separate the expunged air into two channels of high and low speeds, putting the fast stuff up top so the noise is directed upwards. If it works noise on the ground could be reduced by more than half (about 6 dB).
Sounds like a great idea — miles ahead of this perforated-metal idea that was proposed decades ago, when commercial jets first arrived on the scene. Still, Dimitri's idea is years away, so if you're looking for a little more immediate solution to your engine-noise problems, you may want to take a look at this Geared Turbofan engine that's just been cleared for flight testing.