It would be interesting to quantify the difference, but for what it's worth the restaurant example at the beginning is described as having sound-absorbing walls

It would be interesting to quantify the difference, but for what it's worth the restaurant example at the beginning is described as having sound-absorbing walls, so that must not be enough by itself, and all the other examples seem to involve rooms that have adjustable characteristics, something that would be hard to achieve without active systems.