Ae sfx a3
This causes any sound within the sector to have an echo effect.
Place an M[HearingDistance,1000+EchoAmount] in any sector which does not have a Lo-Tag (although there are some exceptions). For HearingDistance, a value of 1024 is equal to the largest grid square in Build. For EchoAmount, you can use any value between 0-255 (0 being the least amount of echo).