Endless volume escalation is known as Lombard Effect: https://en.wikipedia.org/wiki/Lombard_effect

At parties it is mainly due to room's echo.

The best and cheapest is open-air, where voices fly into the sky and never return, it would take like a thousand of people before it stops being enough.

Second best are large open windows, missing walls (porch/balcony) or multiple rooms.

Beyond that I don't think there can be a solution without some sort of room soundproofing, which is usually no-go for rented spaces and private houses. The closest one can get is to maximize soft surfaces (rugs, curtains esp. along walls).

Speaking of which, I wish bars, restaurants and other venues were required to place echo reducers on the ceiling, such simple and cheap measure would dramatically improve ability to talk there when they're full.

> Speaking of which, I wish bars, restaurants and other venues were required to place echo reducers on the ceiling, such simple and cheap measure would dramatically improve ability to talk there when they're full.

It's possible they aren't aware, but I have to wonder if it's sometimes intentional. As someone who doesn't drink, I find most bars close to if not entirely intolerable as places to hang out in, not because I mind being around other people drinking, but because they're always so loud. I've always assumed that drinking is what makes this tolerable to people, so now that you bring this up, the idea that this could be a way to sell more alcohol occurs to me. Probably a silly conspiracy theory, but who knows!