I have two DS, 6 and 4 and they are SO loud. The eldest particularly speaks so loudly he's always shouting. If you were across a field and you were trying to hear him, you'd probably be fine. There's nothing wrong with his hearing. The little one also shouts, and makes silly noises, also very loudly. Together, in normal conversation they're pretty much bellowing at each other, and when they wind each other up and raise voices it's unbearably loud.
Me and DH say continuously- indoor voices, quiet voices, I'm not going to answer until you ask that at a normal volume, shhhh, DS you're shouting and we are right here.
What else can we be doing? We don't really call between rooms or floors, neither DH or myself speaks particularly loudly. It's driving me bonkers.