Working with soundblocking lines and sound environments in (Z)Doom was aways a pain and more like "try and error" instead of planning what monsters can hear when and where. boris (trivia: some people still know him as Tarin, one of the most famous and oldest members in the community) has recently released and updated his DoomBuilder 2 plugin Sound Propagation Mode which finally makes these tasks much easier. It visualises the way sound travels through a map and also shows what sectors are affected by a sound environment setting. For more information just check the official thread over at ZDoom.org