"Creates a sound as loud as a car door closing" -> I assume this means at ground level? I can't imagine even the propulsion being that quiet let alone the sonic boom.
Yes, the noise level is measured on the ground directly below the flight path of the plane.
Interestingly, it’s not just the volume but also the pattern of the boom that can be altered by changing the design of the plane. There’s a great discussion of this here: https://www.elidourado.com/p/50-years-supersonic-ban
(Scroll down to the images of the sound wave)
It’s nice when they put it like that. Now imagine you trying to relax or concentrate in your home and hearing a “car door closing”, every minute, regularly, all day. And if in the end it sounds more like the car’s tire blowing up - well… “we are looking at ways to resolve the issue”, “we are aware of the issue and working on it”, “you are the only one complaining”, “it looks you may be too sensitive to noise”, and so on. Who cares in the end. It’s just people.
