This is indeed a very good question.
I don't know the legislation where you are, but most European countries have one for sound levels in public environments. However, most of the time it is completely unrelated to the limits imposed on workplaces, and has actually little to do with health and safety at all. For instance, in France, the level is limited to 105 dB-A (Leq for 15 min, 120 dB-SPL peak). No doubt that there's enough in this to induce hearing loss.
The crazy thing in all this is that these loud public event generally don't run themselves by themselves, and the public is generally not left on its own. There is a lot of staff, and while some of them can wear ear plugs, a fair number of them can't because they must hear orders from customers, or because they have the hand on the volume knob and are supposed to check what's going on sound-wise...
I used to teach to these guys, sound technicians/engineers, a short introduction to hearing. What I remember is that there's a lot of myth and legend in the field: they know next to nothing about how to preserve their ear even though this is their primary professional tool (deaf sound engineers don't have the best reputation). Backstage, they hear things like "ears are like a muscle, you need to train them: the louder the sound, the stronger your ears become". Actually once you've killed that myth (by playing simulations of hearing loss, cochlear-implant, tinnitus, hyperacusis...), they get pretty concerned. And with the concern for their own health, you may expect that they would be more concerned about the public's health.
Now, only when this knowledge is ubiquitous in the profession will the tech guys have the guts to tell the producer/employer that they shouldn't do it. In the meantime the only thing that can bend these people, is the prospect of getting brought to court for rendering someone deaf.
And actually it already happened. I only know of examples in France, but it must have happened in America too. In France they talk about a concert of Ben Harper in Grenoble (29 March 2000) where 6 people in the audience ended up in hospital for ear damage, and one of them attacked the organizers in court (I added a bit more details about in the PS). I haven't been able to check more, but the legend says he won, and the whole benefice from the concert went in the payment of compensations for that person. Since, concerts are apparently limited at 95 dB-A in Grenoble. People don't seem to have noticed, but nobody was sent again to the hospital. Another example: U2, Marseille July 1993, same story. I'm sure there's enough material to scare the organizers out of doing the stupid thing.
So I think the right discourse is to stress that keeping levels low is not about making the old neighbours less cranky, it's not about being nice... it's about health and safety, about preserving your professional tools (be they employee or your own ears) and about running your business in a sustainable way. The last straw is that the only argument against turning down the level is that "people won't enjoy is as much". But while there's actually no proof of that at all, there quite a large literature on NIHL... (more on that in the PPS)
PS: More about the case in Grenoble. Again this is what I've heard from sound engineers. These big concerts use directional systems (line array, or phased array, or "system V-DOSC"). The common problem that sound engineers face is that there's a large crowd, and sound needs to travel and gets attenuated while doing so. With a directional system, you can try to have a more homogenous sound level in the audience: you jack up the higher beams to reach afar, but keep the lower beams relatively softer to avoid deafening (instantly) the audience close to the stage. Nice on paper, but if you mistune the system (which may apparently have been the case in Grenoble), you may do worse than good. And even worse, if you don't have that system but are used to it, you may forget that you should not have 95 dB at the console at the back of the audience...
PPS: Regarding how enjoyable loud music is, I think there is quite a large source of evidence that loudness can be subjective and context dependent. Actually this is a trick that experienced sound engineers sometime use: when a musician thinks is not loud enough, for instance, the right thing to do is to lower his level, then when he/she's unhappy, put it back to where it was... that generally makes one happy musician...
Etienne Gaudrain, PhD
UMCG, Afdeling KNO
PO Box 30.001
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