This will not be respected, much less enforced, in any Muslim majority area in Indonesia. Just like the previous regulation from 1978. It is a circular from the Ministry of Religion, which does not have any enforcing mechanism. Even if it did, no hapless Satpol PP guy is going to risk his skin to ask a mosque to turn down their loudspeaker.
I disagree. This new move is actually quite significant and different from the 1978 one, because
1) It specifies a sound level (100Db)
2) It has been publicly supported by various muslim organisations
3) Socialisation is being carried out at the offending buildings, and implementing guidance has been issued [why would they bother if they thought it would have zero effect]
Clearly there will not be widespread compliance, but at least it could stop them getting even louder. And as a first step it seems to be as much as could reasonably be done. Also the comparison to dogs barking I thought was actually quite deliberate and quite clever, a kind of signal to minorities that their concerns are being addressed.
Don't forget these buildings are attacking the population daily, and this does have health effects, especially on vulnerable people (the Havana Syndrome issue where US embassies are attacked by sound waves is an interesting comparison). Such health effects include disrupted sleep meaning bodies take longer to recover from illness, PTSD from loud noises like ex-soldiers suffer (shell shock), lack of focus during everyday tasks, traffic accidents through extreme tiredness. There is no doubt at all that it indirectly causes death in one way or another, difficult to quantify how many exactly.
It's like the anti-money laundering rules. At first everyone says the rich will just ignore them. But then gradually over the years people start to realise that they do have some effect, even if rules are still often broken, actually having the rules is a start and something to build on. There are more hoops to jump through, it becomes harder to launder money, though still not impossible.
Or you can compare it to the battle to phase out premium benzin. People said it won't happen, but very gradually it is happening. Pertalite has pretty much replaced premium, and the process is only moving in one direction as far as I can see. People said motorists would blockade parliament if they ever tried, but the government found a way.
So, I'm optimistic.