[null and void]

No, sorry. I'm guessing-and it's just a guess!-that 40,000+ feet might do it.

It's a bit like asking how tall is a mountain, they're a lot smaller in Brittan than in the Andes.

It also depends on how much boom is acceptable, and that varys a lot from individual to individual. I was raised on Marine Corps air bases, and I miss sonic booms...

[Tijeras_Slim]

It also depends on how much boom is acceptable, and that varys a lot from individual to individual.

Conservative: "The sound of freedom, cool!"

Liberal: "How dare those warmongers annoy me!"

[CathyRyan]

Thanks! :)