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