Let's say there is a multiplayer 2D game and a 2D spatial sound system, in which sound volume decreases, when distance to the sound position increases. E.g. explosion happens. Should player hear it if it's outside the camera's viewport zone? Basically, how big should a max distance to sound position should be? How is it handled in other 2D games?
I would say it works best if you can hear things that are just outside the screen too. This helps in creating the illusion that the world continues outside the screen. Try to set it up so that the volume is linearly connected to the distance from the player.
volume = distance/maxAudibleDistance
maxAudibleDistance would be for example 75% of your screen size, assuming your character is always in the center of the screen. Then you could hear explosions faintly if they happen 25% distance outside your screen.