It's been nearly 10 years since the supersonic airliner was permanently grounded, and the race is now on to build the successor to the megafast plane. But before any proposed designs take flight, researchers at Boeing, Lockheed Martin, and NASA are working to minimize the sound heard on the ground as a result of sonic-boom emissions. Recent studies indicate  that they can potentially soften the noise to an almost undetectable level for folks. Here's where it falls on the decibel sound scale.
[Concorde Image: Tony Emmett  via Shutterstock]