Re: 22 suppressor distance heard?
One of the ways to look at is that it is relative to ambient noise.
An 18"+ bolt action 22LR with subsonic loads and a decent suppressor is very quiet. How far away can it be heard? It comes down to the ambient noise level.
Compare it to light:
A small flashlight might not be noticed in the daytime, but out in a field in a dark night it could hardly be missed. If you are our on your deck in town, in the afternoon, in conversation, with all the ambient noise that goes with it: the above .22 probably would not be noticed over the fence in the neighbor's yard. If it is at night out on a lake or another open area with very little ambient noise, I would say you could still hear the shot noise about as far away as someone clearing their throat.
Another way of looking at it, a suppressed .22LR is usually quieter that the impact of projectile into dirt if you are within about 25 yards of a berm.
Hope that helps.