Not a bad concept... Although it's not very clear in AoE 2. Maybe we can simplify it: have one attack sound when your units get attacked and another one when buildings get attacked? It would help assess the severity of the threat.  (I've had my base overrun more than once without even realising because I was so engaged in a battle somewhere else on the map, and likewise, have overrun people's base without them realising because they were fighting somewhere else) Those distance and time