I get what you're trying to accomplish, disincentivize people against honking excessively, but it's a bit like trying to prevent stabbings by only selling knives without handles.
I think we should be looking into more effective ways for people to communicate among vehicles, honestly.
But this is precisely what makes no sense as the requirement for the high volume never came from how loud it was to the person that hit the horn in the first place. The driver you're trying to signal is going to be inside a vehicle therefore it needs to be loud enough to be heard from inside a vehicle.
False
Something like https://news.ycombinator.com/item?id=31309299 can be thought of to try to solve both problems instead of limiting good solutions to be only those for a single perspective.
Loudness falls off pretty fast.
You shouldn't be using your horn often enough to do that anyway, and if a single honk is loud enough to damage your hearing in this case, it's also loud enough to damage the hearing of a pedestrian walking near you.
I say do it. It'd be a strong disincentive to use your horn unnecessarily.
If you're going 70 and want to signal to the guy left of you to not merge into you "it's too loud for a pedestrian to safely stand right next to" isn't very relevant (in both perspectives). At the same time if you're going <5 mph on a comparatively quiet backed up street there is no reason it has to be the same volume as the first case.