For hearing the sounds generate sound events that the agents can listen to. An event contain the type of sound, sound range, position and how generated.
To cut down on events only sounds that matter to the agents need to generate events. Explosions, gun shots and doors can sends events for example.
Each event can have it's own range how far one can hear it. A door might be open slowly without making much noise but a gun shoot can be heard from the next building.
An agent can have a max range that he can hear things inside. Everything outside that range he ignores.