[CountHackulus]

At 70PNLdB, I doubt anyone in their car could hear it. In fact pretty much only rural quiet areas will hear it. Though I'm sure there's going to be some "concerned citizens" that claim that the sonic booms are causing their children migraines, or something similar.

Still, living at one end of Canada and having friends at the other end, I'm excited for the possibility quiet overland supersonic flight.

[Anechoic]

At 70PNLdB, I doubt anyone in their car could hear it. In fact pretty much only rural quiet areas will hear it.

70 PNL dB is fairly loud, it will be very noticeable in urban areas and extremely disruptive in rural areas. 65 dB Ldn is the target for normal aircraft and most experts agree that limit is way too high.

The research represents a significant decrease in noise from supersonic aircraft, but we're a long way from "quiet."

[CountHackulus]

Got any sources for that? I'm interested in reading that research.

Couple anecdotes: I work in a semi rural neighborhood that's 2km from a regional airport (a bit off to the side of the approach path). I work right next to a window and haven't once heard an airplane go by. Now, this might be due to our shielded glass and white noise generators in the ceiling, but that's not bad.

Second anecdote, there was an airport downtown on the water that was re-opening with an airline running Bombardier Q400s (Porter Airlines at Billy Bishop). There was a group of protesters that were claiming that the noise would ruin the quiet of a nearby spit. So on the launch day, before the sun rose, they gathered at the spit to protest. Unfortunately for them, they missed the first flight as their talking had drowned it out.

Maybe it's just because I lived next to the railroad tracks for 20 years, but I say, bring on the jets.

[Anechoic]

Got any sources for that? I'm interested in reading that research.

Nothing specific off hand, I used to work for a firm that did aviation noise analysis and this was something I heard a lot from colleagues at the firm and other firms. A starting point might be a couple of presentations from that firm that don't discuss the appropriatness of 65 Ldn directly, but discuss how that criterion is not always adequate:

http://www.hmmh.com/cmsdocuments/UCD_Mar07_Eagan.pdf

http://www.hmmh.com/cmsdocuments/DNL_History_Eagan_FAA_NER20...

http://www.hmmh.com/cmsdocuments/Eagan_Beyond_DNL65.pdf

I work in a semi rural neighborhood that's 2km from a regional airport (a bit off to the side of the approach path).

Approaches generally speaking tend to be much quieter than departures. What airport? Depending on a bunch of factors (noise abatement procedures, prevailing winds, approach tracks, fleet mix, etc) it's entirely possible it might not be loud where you are, vs another location. It's also possible that you're less sensitive to the noise because that you are working rather than trying to sleep (and also due to possible sound insulation measures as indicated).

Second anecdote, there was an airport downtown on the water [..] So on the launch day, before the sun rose,

Key word being "water"and "before the sun rose" - depending on temperature gradients (which tend to occur near sunrise and sunset) and wind direction sound propagation over water can have very unusual effects. In particular, if air temperatures high up in the atmosphere are cooler than air temperatures just above the water, sound waves can "bend" upwards to that folks on the ground will experience lower SPL's compared to what they might hear when the air temperature is more homogeneous.

[ismarc]

More anecdotes, but, I lived 1 1/2 miles perpendicular to the most frequent runway of an airport. If you were outside, you could hear every plane take off and it disturbed an otherwise perfect place to live. However, with zero noise considerations in building, couldn't hear a thing inside. On the other hand, I now live within 2 miles of a medium sized metro area and the normal sound of traffic is louder than the planes were. So while I never took db readings, environment is going to play a huge impact, but even minimal insulation will make it inaudible.

[rbanffy]

What noise levels current airliners generate? We can then have a better idea of how noisy these new airliners would be.

[rplnt]

It's not about the noise in general. It's about the sonic boom. For example, Concorde's sonic boom: http://www.youtube.com/watch?v=oMOyeuDKAlg

[rbanffy]

Indeed - a sudden boom is more disturbing than a rumble.

Still, if it can be made quiet enough not to scare people, it could be inspiring. You hear a bang in time see a man-made object traveling above Mach 2.

Or 3, 4, 5...