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In Japan, HST noise is limited to 70-75 dB at 25 meters from the track.

The 108 dB sonic boom will be experienced over a much larger area.

> They are in fact the same. 108dB loud

There is a tonne of progress in atmospheric modellingn that lets us predict how the thump will be refracted to and reflected from the ground. So yes, you still have the same energy being dumped into the atmosphere. But less of it turns into audible sound, less of it arrives in one go, and less of it ever reaches the ground in an audible form.

108 dB is the proposed FAA allowable pressure at the surface of the earth. They didn't come up with this number arbitrarily they did it with consultation with the supersonic plane companies and if those companies could achieve much less than 108dB then the proposed limit would be lower.

A sonic boom and a loud sound are not, in fact, the same thing.

If that loud sound is roughly boom-like in shape and texture, and caused by an object moving faster through its medium than the speed of sound of its medium, then they are, in fact, the same thing.