Don't Shout
I just realized I've never shouted as-loud-as-I-can ever in my life.
A shout can potentially travel for about 100m. A circle with that as radius is 31400 square meters, roughly 3 hectares. Earth's total land is about 150 trillion square meters. 150 trillion ÷ 31,400 = about 4.8 billion people. At 8.3 billion, we get 150 trillion ÷ 8.3 billion = 18,000, which gets everyone a safe-shout radius of 75m. 25% less than ideal.
Of course, not all humanity is evenly spaced out. But I wonder if 4.8 might be the ideal population of humans on the planet.