Just been watching the tail-end of a Japanese TV programme explaining the most recent results of tests they did on their joint JAXA/Swedish supersonic plane.
The Japanese Space Agency Tested a Supersonic Plane With Less Sonic Boom | Motherboard
Their main discovery was the sonic boom created by the aircraft's profile is roughly 1/4 that of Concorde.
To get the public to understand this concept, they said, imagine the clap of thunder that accompanies a very close flash of lightning. That would be the Concorde sonic boom. Then imagine the same flash of lightning some distance away and the resultant rumble of thunder, approximating the relative sound from JAXA's test frame.
Some footage of their testing concepts here, but no sound?
http://www.bing.com/videos/search?q=...9879D939AD2767