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.

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